abducens nerve

sixth cranial nerve; responsible for contraction of one of the extraocular muscles

absolute refractory period

time during an action period when another action potential cannot be generated because the voltage-gated Na⁺ channel is inactivated

absorption

passage of digested products from the intestinal lumen through mucosal cells and into the bloodstream or lacteals

absorptive state

also called the fed state; the metabolic state occurring during the first few hours after ingesting food in which the body is digesting food and absorbing the nutrients

accessory digestive organ

includes teeth, tongue, salivary glands, gallbladder, liver, and pancreas

accessory duct

(also, duct of Santorini) duct that runs from the pancreas into the duodenum

acetyl coenzyme A (acetyl CoA)

starting molecule of the Krebs cycle

acetylcholine (ACh)

neurotransmitter that binds at a motor end-plate to trigger depolarization

acid

compound that releases hydrogen ions in solution

acinus

cluster of glandular epithelial cells in the pancreas that secretes pancreatic juice in the pancreas

acromegaly

disorder in adults caused when abnormally high levels of GH trigger growth of bones in the face, hands, and feet

acrosome

cap-like vesicle located at the anterior-most region of a sperm that is rich with lysosomal enzymes capable of digesting the protective layers surrounding the oocyte

acrosomal reaction

release of digestive enzymes by sperm that enables them to burrow through the corona radiata and penetrate the zona pellucida of an oocyte prior to fertilization

action potential
change in voltage of a cell membrane in response to a stimulus that results in transmission of an electrical signal; unique to neurons and muscle fibers

activation gate

part of the voltage-gated Na⁺ channel that opens when the membrane voltage reaches threshold

adenylyl cyclase

membrane-bound enzyme that converts ATP to cyclic AMP, creating cAMP, as a result of G-protein activation

adenosine triphosphate (ATP)

nucleotide containing ribose and an adenine base that is essential in energy transfer

adrenal cortex

outer region of the adrenal glands consisting of multiple layers of epithelial cells and capillary networks that produces mineralocorticoids and glucocorticoids

adrenal glands

endocrine glands located at the top of each kidney that are important for the regulation of the stress response, blood pressure and blood volume, water homeostasis, and electrolyte levels

adrenal medulla

inner layer of the adrenal glands that plays an important role in the stress response by producing epinephrine and norepinephrine

adrenal medulla

interior portion of the adrenal (or suprarenal) gland that releases epinephrine and norepinephrine into the bloodstream as hormones

adrenergic

synapse where norepinephrine is released, which binds to α- or β-adrenergic receptors

adrenocorticotropic hormone (ACTH)
anterior pituitary hormone that stimulates the adrenal cortex to secrete corticosteroid hormones (also called corticotropin)

alar plate
developmental region of the spinal cord that gives rise to the posterior horn of the gray matter

alimentary canal

continuous muscular digestive tube that extends from the mouth to the anus

alkaloid

substance, usually from a plant source, that is chemically basic with respect to pH and will stimulate bitter receptors

alpha (α)-adrenergic receptor

one of the receptors to which epinephrine and norepinephrine bind, which comes in three subtypes: α₁, α₂, and α₃

alarm reaction

the short-term stress, or the fight-or-flight response, of stage one of the general adaptation syndrome mediated by the hormones epinephrine and norepinephrine

aldosterone

hormone produced and secreted by the adrenal cortex that stimulates sodium and fluid retention and increases blood volume and blood pressure

allantois

finger-like outpocketing of yolk sac forms the primitive excretory duct of the embryo; precursor to the urinary bladder

allele

alternative forms of a gene that occupy a specific locus on a specific gene

alpha cell

pancreatic islet cell type that produces the hormone glucagon

alveoli

(of the breast) milk-secreting cells in the mammary gland

amacrine cell

type of cell in the retina that connects to the bipolar cells near the outer synaptic layer and provides the basis for early image processing within the retina

amino acid

building block of proteins; characterized by an amino and carboxyl functional groups and a variable side-chain

aminopeptidase

brush border enzyme that acts on proteins

amnion

transparent membranous sac that encloses the developing fetus and fills with amniotic fluid

amniotic cavity

cavity that opens up between the inner cell mass and the trophoblast; develops into amnion

ampulla

in the ear, the structure at the base of a semicircular canal that contains the hair cells and cupula for transduction of rotational movement of the head

ampulla

(of the uterine tube) middle portion of the uterine tube in which fertilization often occurs

amygdala

nucleus deep in the temporal lobe of the cerebrum that is related to memory and emotional behavior

anabolic hormones

hormones that stimulate the synthesis of new, larger molecules

anabolic reactions

reactions that build smaller molecules into larger molecules

anal canal

final segment of the large intestine

anal column

long fold of mucosa in the anal canal

anal sinus

recess between anal columns

anaphase

third stage of mitosis (and meiosis), during which sister chromatids separate into two new nuclear regions of a dividing cell

anatomical sphincter

smooth or skeletal muscle surrounding the lumen of a vessel or hollow organ that can restrict flow when contracted

anchoring junction

mechanically attaches adjacent cells to each other or to the basement membrane

angiotensin-converting enzyme (ACE)

enzyme produced by the lungs that catalyzes the reaction of inactive angiotensin I into active angiotensin II

angiotensin I

protein produced by the enzymatic action of renin on angiotensinogen; inactive precursor of angiotensin II

angiotensin II

protein produced by the enzymatic action of ACE on inactive angiotensin I; actively causes vasoconstriction and stimulates aldosterone release by the adrenal cortex

angiotensin-converting enzyme

the enzyme that converts angiotensin I to angiotensin II

angiotensinogen

inactive protein in the circulation produced by the liver; precursor of angiotensin I; must be modified by the enzymes renin and ACE to be activated

anion

atom with a negative charge

anosmia

loss of the sense of smell; usually the result of physical disruption of the first cranial nerve

anterior column

white matter between the anterior horns of the spinal cord composed of many different groups of axons of both ascending and descending tracts

anterior horn

gray matter of the spinal cord containing multipolar motor neurons, sometimes referred to as the ventral horn

anterior median fissure

deep midline feature of the anterior spinal cord, marking the separation between the right and left sides of the cord

anterior spinal artery

blood vessel from the merged branches of the vertebral arteries that runs along the anterior surface of the spinal cord

antidiuretic hormone (ADH)

also known as vasopressin, a hormone that increases the volume of water reabsorbed from the collecting tubules of the kidney

antidiuretic hormone (ADH)

hypothalamic hormone that is stored by the posterior pituitary and that signals the kidneys to reabsorb water

antrum

fluid-filled chamber that characterizes a mature tertiary (antral) follicle

anuria

absence of urine produced; production of 50 mL or less per day

apical

that part of a cell or tissue which, in general, faces an open space

apocrine secretion

release of a substance along with the apical portion of the cell

appendix

(vermiform appendix) coiled tube attached to the cecum

aquaporin

protein-forming water channels through the lipid bilayer of the cell; allows water to cross; activation in the collecting ducts is under the control of ADH

aqueous humor

watery fluid that fills the anterior chamber containing the cornea, iris, ciliary body, and lens of the eye

arachnoid granulation

outpocket of the arachnoid membrane into the dural sinuses that allows for reabsorption of CSF into the blood

arachnoid mater

middle layer of the meninges named for the spider-web–like trabeculae that extend between it and the pia mater

arachnoid trabeculae

filaments between the arachnoid and pia mater within the subarachnoid space

areola

highly pigmented, circular area surrounding the raised nipple and containing areolar glands that secrete fluid important for lubrication during suckling

ascending colon

first region of the colon

ascending tract

central nervous system fibers carrying sensory information from the spinal cord or periphery to the brain

astrocyte

glial cell type of the CNS that provides support for neurons and maintains the blood-brain barrier

ATP synthase

protein pore complex that creates ATP

atrial natriuretic peptide (ANP)

peptide hormone produced by the walls of the atria in response to high blood pressure, blood volume, or blood sodium that reduces the reabsorption of sodium and water in the kidneys and promotes vasodilation

audition

sense of hearing

auricle

fleshy external structure of the ear

autocrine

chemical signal that elicits a response in the same cell that secreted it

autonomic nervous system (ANS)

functional division of the nervous system that is responsible for homeostatic reflexes that coordinate control of cardiac and smooth muscle, as well as glandular tissue

autosomal chromosome

in humans, the 22 pairs of chromosomes that are not the sex chromosomes (XX or XY)

autosomal dominant

pattern of dominant inheritance that corresponds to a gene on one of the 22 autosomal chromosomes

autosomal recessive

pattern of recessive inheritance that corresponds to a gene on one of the 22 autosomal chromosomes

axillary nerve

systemic nerve of the arm that arises from the brachial plexus

axon

single process of the neuron that carries an electrical signal (action potential) away from the cell body toward a target cell

axon hillock

tapering of the neuron cell body that gives rise to the axon

axon segment

single stretch of the axon insulated by myelin and bounded by nodes of Ranvier at either end (except for the first, which is after the initial segment, and the last, which is followed by the axon terminal)

axon terminal

end of the axon, where there are usually several branches extending toward the target cell

axoplasm

cytoplasm of an axon, which is different in composition than the cytoplasm of the neuronal cell body

bacterial flora

bacteria in the large intestine

Bartholin’s glands

(also, greater vestibular glands) glands that produce a thick mucus that maintains moisture in the vulva area; also referred to as the greater vestibular glands

basal forebrain

nuclei of the cerebrum related to modulation of sensory stimuli and attention through broad projections to the cerebral cortex, loss of which is related to Alzheimer’s disease

basal lamina

thin extracellular layer that lies underneath epithelial cells and separates them from other tissues

basal nuclei

nuclei of the cerebrum (with a few components in the upper brain stem and diencephalon) that are responsible for assessing cortical movement commands and comparing them with the general state of the individual through broad modulatory activity of dopamine neurons; largely related to motor functions, as evidenced through the symptoms of Parkinson’s and Huntington’s diseases

basal plate

developmental region of the spinal cord that gives rise to the lateral and anterior horns of gray matter

base

compound that accepts hydrogen ions (H⁺) in solution

basement membrane

in epithelial tissue, a thin layer of fibrous material that anchors the epithelial tissue to the underlying connective tissue; made up of the basal lamina and reticular lamina

basilar artery

blood vessel from the merged vertebral arteries that runs along the dorsal surface of the brain stem

basilar membrane

in the ear, the floor of the cochlear duct on which the organ of Corti sits

beta (β)-adrenergic receptor

one of the receptors to which epinephrine and norepinephrine bind, which comes in two subtypes: β₁ and β₂

beta (β)-hydroxybutyrate

primary ketone body produced in the body

beta (β)-oxidation

fatty acid oxidation

beta cell

pancreatic islet cell type that produces the hormone insulin

bile

alkaline solution produced by the liver and important for the emulsification of lipids

bile canaliculus

small duct between hepatocytes that collects bile

bile salts

salts that are released from the liver in response to lipid ingestion and surround the insoluble triglycerides to aid in their conversion to monoglycerides and free fatty acids

bilirubin

main bile pigment, which is responsible for the brown color of feces

biogenic amine

class of neurotransmitters that are enzymatically derived from amino acids but no longer contain a carboxyl group

biosynthesis reactions

reactions that create new molecules, also called anabolic reactions

bipolar

shape of a neuron with two processes extending from the neuron cell body—the axon and one dendrite

bipolar cell

cell type in the retina that connects the photoreceptors to the RGCs

blastocoel

fluid-filled cavity of the blastocyst

blastocyst

term for the conceptus at the developmental stage that consists of about 100 cells shaped into an inner cell mass that is fated to become the embryo and an outer trophoblast that is fated to become the associated fetal membranes and placenta

blastomere

daughter cell of a cleavage

blood-brain barrier (BBB)

physiological barrier between the circulatory system and the central nervous system that establishes a privileged blood supply, restricting the flow of substances into the CNS

blood–testis barrier

tight junctions between Sertoli cells that prevent bloodborne pathogens from gaining access to later stages of spermatogenesis and prevent the potential for an autoimmune reaction to haploid sperm

body

mid-portion of the stomach

body mass index (BMI)

relative amount of body weight compared to the overall height; a BMI ranging from 18–24.9 is considered normal weight, 25–29.9 is considered overweight, and greater than 30 is considered obese

body of uterus

middle section of the uterus

bolus

mass of chewed food

bond

electrical force linking atoms

Bowman’s capsule

cup-shaped sack lined by a simple squamous epithelium (parietal surface) and specialized cells called podocytes (visceral surface) that participate in the filtration process; receives the filtrate which then passes on to the PCTs

brachial plexus

nerve plexus associated with the lower cervical spinal nerves and first thoracic spinal nerve

brain

the large organ of the central nervous system composed of white and gray matter, contained within the cranium and continuous with the spinal cord

broad ligament

wide ligament that supports the uterus by attaching laterally to both sides of the uterus and pelvic wall

Broca’s area

region of the frontal lobe associated with the motor commands necessary for speech production and located only in the cerebral hemisphere responsible for language production, which is the left side in approximately 95 percent of the population

Brodmann’s areas

mapping of regions of the cerebral cortex based on microscopic anatomy that relates specific areas to functional differences, as described by Brodmann in the early 1900s

brush border

fuzzy appearance of the small intestinal mucosa created by microvilli

brush border

formed by microvilli on the surface of certain cuboidal cells; in the kidney it is found in the PCT; increases surface area for absorption in the kidney

buffer

solution containing a weak acid or a weak base that opposes wide fluctuations in the pH of body fluids

bulbourethral glands

(also, Cowper’s glands) glands that secrete a lubricating mucus that cleans and lubricates the urethra prior to and during ejaculation

calcitonin

peptide hormone produced and secreted by the parafollicular cells (C cells) of the thyroid gland that functions to decrease blood calcium levels

calorie

amount of heat it takes to raise 1 kg (1000 g) of water by 1 °C

calyces

cup-like structures receiving urine from the collecting ducts where it passes on to the renal pelvis and ureter

capsaicin

molecule that activates nociceptors by interacting with a temperature-sensitive ion channel and is the basis for “hot” sensations in spicy food

capacitation

process that occurs in the female reproductive tract in which sperm are prepared for fertilization; leads to increased motility and changes in their outer membrane that improve their ability to release enzymes capable of digesting an oocyte’s outer layers

carbohydrate

class of organic compounds built from sugars, molecules containing carbon, hydrogen, and oxygen in a 1-2-1 ratio

cardia

(also, cardiac region) part of the stomach surrounding the cardiac orifice (esophageal hiatus)

carotid canal

opening in the temporal bone through which the internal carotid artery enters the cranium

carrier

heterozygous individual who does not display symptoms of a recessive genetic disorder but can transmit the disorder to his or her offspring

catabolic hormones

hormones that stimulate the breakdown of larger molecules

catabolic reactions

reactions that break down larger molecules into their constituent parts

cation

atom with a positive charge

cauda equina

bundle of spinal nerve roots that descend from the lower spinal cord below the first lumbar vertebra and lie within the vertebral cavity; has the appearance of a horse’s tail

caudate

nucleus deep in the cerebrum that is part of the basal nuclei; along with the putamen, it is part of the striatum

cecum

pouch forming the beginning of the large intestine

celiac ganglion

one of the collateral ganglia of the sympathetic system that projects to the digestive system

cell cycle

life cycle of a single cell, from its birth until its division into two new daughter cells

cell junction

point of cell-to-cell contact that connects one cell to another in a tissue

cellular respiration

production of ATP from glucose oxidation via glycolysis, the Krebs cycle, and oxidative phosphorylation

cementum

bone-like tissue covering the root of a tooth

central canal

hollow space within the spinal cord that is the remnant of the center of the neural tube

central nervous system (CNS)

anatomical division of the nervous system located within the cranial and vertebral cavities, namely the brain and spinal cord

central neuron

specifically referring to the cell body of a neuron in the autonomic system that is located in the central nervous system, specifically the lateral horn of the spinal cord or a brain stem nucleus

central sulcus

surface landmark of the cerebral cortex that marks the boundary between the frontal and parietal lobes

central vein

vein that receives blood from hepatic sinusoids

centromere

region of attachment for two sister chromatids

centrosome

cellular structure that organizes microtubules during cell division

cephalic phase

(also, reflex phase) initial phase of gastric secretion that occurs before food enters the stomach

cerebral aqueduct

connection of the ventricular system between the third and fourth ventricles located in the midbrain

cerebral cortex

outer gray matter covering the forebrain, marked by wrinkles and folds known as gyri and sulci

cerebrum

region of the adult brain that develops from the telencephalon and is responsible for higher neurological functions such as memory, emotion, and consciousness

cerebellum

region of the adult brain connected primarily to the pons that developed from the metencephalon (along with the pons) and is largely responsible for comparing information from the cerebrum with sensory feedback from the periphery through the spinal cord

cerebral hemisphere

one half of the bilaterally symmetrical cerebrum

cerebrospinal fluid (CSF)

circulatory medium within the CNS that is produced by ependymal cells in the choroid plexus filtering the blood

cervical plexus

nerve plexus associated with the upper cervical spinal nerves

cervix

elongate inferior end of the uterus where it connects to the vagina

chief cell

gastric gland cell that secretes pepsinogen

checkpoint

progress point in the cell cycle during which certain conditions must be met in order for the cell to proceed to a subsequence phase

chemical digestion

enzymatic breakdown of food

chemical synapse

connection between two neurons, or between a neuron and its target, where a neurotransmitter diffuses across a very short distance

chemoreceptor

sensory receptor cell that is sensitive to chemical stimuli, such as in taste, smell, or pain

cholecystokinin (CCK)

hormone that stimulates the release of pancreatic lipase and the contraction of the gallbladder to release bile salts

cholinergic

synapse at which acetylcholine is released and binds to the nicotinic or muscarinic receptor

cholinergic system

neurotransmitter system of acetylcholine, which includes its receptors and the enzyme acetylcholinesterase

choroid

highly vascular tissue in the wall of the eye that supplies the outer retina with blood

choroid plexus

specialized structure containing ependymal cells that line blood capillaries and filter blood to produce CSF in the four ventricles of the brain

chorion

membrane that develops from the syncytiotrophoblast, cytotrophoblast, and mesoderm; surrounds the embryo and forms the fetal portion of the placenta through the chorionic villi

chorionic membrane

precursor to the chorion; forms from extra-embryonic mesoderm cells

chorionic villi

projections of the chorionic membrane that burrow into the endometrium and develop into the placenta

chromaffin

neuroendocrine cells of the adrenal medulla

chromaffin cells

neuroendocrine cells of the adrenal medulla that release epinephrine and norepinephrine into the bloodstream as part of sympathetic system activity

chylomicron

large lipid-transport compound made up of triglycerides, phospholipids, cholesterol, and proteins

chyme

soupy liquid created when food is mixed with digestive juices

chylomicrons

vesicles containing cholesterol and triglycerides that transport lipids out of the intestinal cells and into the lymphatic and circulatory systems

chymotrypsin

pancreatic enzyme that digests protein

chymotrypsinogen

proenzyme that is activated by trypsin into chymotrypsin

ciliary body

smooth muscle structure on the interior surface of the iris that controls the shape of the lens through the zonule fibers

ciliary ganglion

one of the terminal ganglia of the parasympathetic system, located in the posterior orbit, axons from which project to the iris

circle of Willis

unique anatomical arrangement of blood vessels around the base of the brain that maintains perfusion of blood into the brain even if one component of the structure is blocked or narrowed

circular fold

(also, plica circulare) deep fold in the mucosa and submucosa of the small intestine

citric acid cycle

also called the Krebs cycle or the tricarboxylic acid cycle; converts pyruvate into CO₂ and high-energy FADH₂, NADH, and ATP molecules

cleavage

form of mitotic cell division in which the cell divides but the total volume remains unchanged; this process serves to produce smaller and smaller cells

cleavage furrow

contractile ring that forms around a cell during cytokinesis that pinches the cell into two halves

clitoris

(also, glans clitoris) nerve-rich area of the vulva that contributes to sexual sensation during intercourse

cochlea

auditory portion of the inner ear containing structures to transduce sound stimuli

cochlear duct

space within the auditory portion of the inner ear that contains the organ of Corti and is adjacent to the scala tympani and scala vestibuli on either side

codominance

pattern of inheritance that corresponds to the equal, distinct, and simultaneous expression of two different alleles

collateral ganglia

ganglia outside of the sympathetic chain that are targets of sympathetic preganglionic fibers, which are the celiac, inferior mesenteric, and superior mesenteric ganglia

colloid

liquid mixture in which the solute particles consist of clumps of molecules large enough to scatter light

colloid

viscous fluid in the central cavity of thyroid follicles, containing the glycoprotein thyroglobulin

colon

part of the large intestine between the cecum and the rectum

common bile duct

structure formed by the union of the common hepatic duct and the gallbladder’s cystic duct

common carotid artery

blood vessel that branches off the aorta (or the brachiocephalic artery on the right) and supplies blood to the head and neck

common hepatic duct

duct formed by the merger of the two hepatic ducts

conceptus

pre-implantation stage of a fertilized egg and its associated membranes

cone photoreceptor

one of the two types of retinal receptor cell that is specialized for color vision through the use of three photopigments distributed through three separate populations of cells

continuous conduction

slow propagation of an action potential along an unmyelinated axon owing to voltage-gated Na⁺ channels located along the entire length of the cell membrane

contralateral

word meaning “on the opposite side,” as in axons that cross the midline in a fiber tract

cornea

fibrous covering of the anterior region of the eye that is transparent so that light can pass through it

corona radiata

in an oocyte, a layer of granulosa cells that surrounds the oocyte and that must be penetrated by sperm before fertilization can occur

corpus albicans

nonfunctional structure remaining in the ovarian stroma following structural and functional regression of the corpus luteum

corpus callosum

large white matter structure that connects the right and left cerebral hemispheres

corpus cavernosum

either of two columns of erectile tissue in the penis that fill with blood during an erection

corpus luteum

transformed follicle after ovulation that secretes progesterone

corpus spongiosum

(plural = corpora cavernosa) column of erectile tissue in the penis that fills with blood during an erection and surrounds the penile urethra on the ventral portion of the penis

cortical nephrons

nephrons with loops of Henle that do not extend into the renal medulla

cortical reaction

following fertilization, the release of cortical granules from the oocyte’s plasma membrane into the zona pellucida creating a fertilization membrane that prevents any further attachment or penetration of sperm; part of the slow block to polyspermy

cortisol

glucocorticoid important in gluconeogenesis, the catabolism of glycogen, and downregulation of the immune system

countercurrent multiplier system

involves the descending and ascending loops of Henle directing forming urine in opposing directions to create a concentration gradient when combined with variable permeability and sodium pumping

covalent bond

chemical bond in which two atoms share electrons, thereby completing their valence shells

cranial nerve

one of twelve nerves connected to the brain that are responsible for sensory or motor functions of the head and neck

cranial nerve ganglion

sensory ganglion of cranial nerves

craniosacral system

alternate name for the parasympathetic division of the autonomic nervous system that is based on the anatomical location of central neurons in brain-stem nuclei and the lateral horn of the sacral spinal cord; also referred to as craniosacral outflow

crown

portion of tooth visible superior to the gum line

cupula

specialized structure within the base of a semicircular canal that bends the stereocilia of hair cells when the head rotates by way of the relative movement of the enclosed fluid

cuspid

(also, canine) pointed tooth used for tearing and shredding food

cyclic adenosine monophosphate (cAMP)

second messenger that, in response to adenylyl cyclase activation, triggers a phosphorylation cascade

cyclin

one of a group of proteins that function in the progression of the cell cycle

cyclin-dependent kinase (CDK)

one of a group of enzymes associated with cyclins that help them perform their functions

cystic duct

duct through which bile drains and enters the gallbladder

cytokinesis

final stage in cell division, where the cytoplasm divides to form two separate daughter cells

defecation

elimination of undigested substances from the body in the form of feces

delta cell

minor cell type in the pancreas that secretes the hormone somatostatin

denaturation

change in the structure of a molecule through physical or chemical means

dendrite

one of many branchlike processes that extends from the neuron cell body and functions as a contact for incoming signals (synapses) from other neurons or sensory cells

deoxyribonuclease

pancreatic enzyme that digests DNA

deoxyribonucleic acid (DNA)

deoxyribose-containing nucleotide that stores genetic information

depolarization

change in a cell membrane potential from rest toward zero

deglutition

three-stage process of swallowing

dehydration

state of containing insufficient water in blood and other tissues

dens

tooth

dentin

bone-like tissue immediately deep to the enamel of the crown or cementum of the root of a tooth

dentition

set of teeth

descending colon

part of the colon between the transverse colon and the sigmoid colon

descending tract

central nervous system fibers carrying motor commands from the brain to the spinal cord or periphery

deciduous tooth

one of 20 “baby teeth”

detrusor muscle

smooth muscle in the bladder wall; fibers run in all directions to reduce the size of the organ when emptying it of urine

diabetes mellitus

condition caused by destruction or dysfunction of the beta cells of the pancreas or cellular resistance to insulin that results in abnormally high blood glucose levels

diacylglycerol (DAG)

molecule that, like cAMP, activates protein kinases, thereby initiating a phosphorylation cascade

dihydroxyvitamin D

active form of vitamin D required by the intestinal epithelial cells for the absorption of calcium

dipeptidase

brush border enzyme that acts on proteins

diploid

condition marked by the presence of a double complement of genetic material (two sets of chromosomes, one set inherited from each of two parents)

direct pathway

connections within the basal nuclei from the striatum to the globus pallidus internal segment and substantia nigra pars reticulata that disinhibit the thalamus to increase cortical control of movement

disaccharide

pair of carbohydrate monomers bonded by dehydration synthesis via a glycosidic bond

disinhibition

disynaptic connection in which the first synapse inhibits the second cell, which then stops inhibiting the final target

distal convoluted tubules

portions of the nephron distal to the loop of Henle that receive hyposmotic filtrate from the loop of Henle and empty into collecting ducts

disulfide bond

covalent bond formed within a polypeptide between sulfide groups of sulfur-containing amino acids, for example, cysteine

diuresis

excess production of urine

dominant

describes a trait that is expressed both in homozygous and heterozygous form

dominant lethal

inheritance pattern in which individuals with one or two copies of a lethal allele do not survive in utero or have a shortened life span

dorsal (posterior) nerve root

axons entering the posterior horn of the spinal cord

dorsal nucleus of the vagus nerve

location of parasympathetic neurons that project through the vagus nerve to terminal ganglia in the thoracic and abdominal cavities

dorsal (posterior) root ganglion

sensory ganglion attached to the posterior nerve root of a spinal nerve

downregulation

decrease in the number of hormone receptors, typically in response to chronically excessive levels of a hormone

ductus arteriosus

shunt in the pulmonary trunk that diverts oxygenated blood back to the aorta

ductus deferens

(also, vas deferens) duct that transports sperm from the epididymis through the spermatic cord and into the ejaculatory duct; also referred as the vas deferens

ductus venosus

shunt that causes oxygenated blood to bypass the fetal liver on its way to the inferior vena cava

duodenal gland

(also, Brunner’s gland) mucous-secreting gland in the duodenal submucosa

duodenum

first part of the small intestine, which starts at the pyloric sphincter and ends at the jejunum

dura mater

tough, fibrous, outer layer of the meninges that is attached to the inner surface of the cranium and vertebral column and surrounds the entire CNS

dural sinus

any of the venous structures surrounding the brain, enclosed within the dura mater, which drain blood from the CNS to the common venous return of the jugular veins

ectoderm

primary germ layer that develops into the central and peripheral nervous systems, sensory organs, epidermis, hair, and nails

ectopic pregnancy

implantation of an embryo outside of the uterus

Eddinger–Westphal nucleus

location of parasympathetic neurons that project to the ciliary ganglion

effector protein

enzyme that catalyzes the generation of a new molecule, which acts as the intracellular mediator of the signal that binds to the receptor

efferent arteriole

arteriole carrying blood from the glomerulus to the capillary beds around the convoluted tubules and loop of Henle; portion of the portal system

ejaculatory duct

duct that connects the ampulla of the ductus deferens with the duct of the seminal vesicle at the prostatic urethra

elastase

pancreatic enzyme that digests protein

electrical synapse

connection between two neurons, or any two electrically active cells, where ions flow directly through channels spanning their adjacent cell membranes

electrochemical exclusion

principle of selectively allowing ions through a channel on the basis of their charge

electron transport chain (ETC)

ATP production pathway in which electrons are passed through a series of oxidation-reduction reactions that forms water and produces a proton gradient

embryo

developing human during weeks 3–8

embryonic folding

process by which an embryo develops from a flat disc of cells to a three-dimensional shape resembling a cylinder

endocrine gland

groups of cells that release chemical signals into the intercellular fluid to be picked up and transported to their target organs by blood

endoderm

primary germ layer that goes on to form the gastrointestinal tract, liver, pancreas, and lungs

endoneurium

innermost layer of connective tissue that surrounds individual axons within a nerve

endothelium

tissue that lines vessels of the lymphatic and cardiovascular system, made up of a simple squamous epithelium

enamel

covering of the dentin of the crown of a tooth

encapsulated ending

configuration of a sensory receptor neuron with dendrites surrounded by specialized structures to aid in transduction of a particular type of sensation, such as the lamellated corpuscles in the deep dermis and subcutaneous tissue

endocrine gland

tissue or organ that secretes hormones into the blood and lymph without ducts such that they may be transported to organs distant from the site of secretion

endocrine system

cells, tissues, and organs that secrete hormones as a primary or secondary function and play an integral role in normal bodily processes

endogenous

describes substance made in the human body

endometrium

inner lining of the uterus, part of which builds up during the secretory phase of the menstrual cycle and then sheds with menses

energy-consuming phase

first phase of glycolysis, in which two molecules of ATP are necessary to start the reaction

energy-yielding phase

second phase of glycolysis, during which energy is produced

enteric nervous system (ENS)

neural tissue associated with the digestive system that is responsible for nervous control through autonomic connections

enteroendocrine cell

gastric gland cell that releases hormones

enteric nervous system

peripheral structures, namely ganglia and nerves, that are incorporated into the digestive system organs

enteric plexus

neuronal plexus in the wall of the intestines, which is part of the enteric nervous system

enterohepatic circulation

recycling mechanism that conserves bile salts

enterokinase

enzyme located in the wall of the small intestine that activates trypsin

enteropeptidase

intestinal brush-border enzyme that activates trypsinogen to trypsin

ependymal cell

glial cell type in the CNS responsible for producing cerebrospinal fluid

epiblast

upper layer of cells of the embryonic disc that forms from the inner cell mass; gives rise to all three germ layers

epididymis

(plural = epididymides) coiled tubular structure in which sperm start to mature and are stored until ejaculation

epiploic appendage

small sac of fat-filled visceral peritoneum attached to teniae coli

epinephrine

signaling molecule released from the adrenal medulla into the bloodstream as part of the sympathetic response

epinephrine

primary and most potent catecholamine hormone secreted by the adrenal medulla in response to short-term stress; also called adrenaline

epineurium

outermost layer of connective tissue that surrounds an entire nerve

epithalamus

region of the diecephalon containing the pineal gland

equilibrium

sense of balance that includes sensations of position and movement of the head

erythropoietin (EPO)

protein hormone secreted in response to low oxygen levels that triggers the bone marrow to produce red blood cells]

esophageal plexus

neuronal plexus in the wall of the esophagus that is part of the enteric nervous system

esophagus

muscular tube that runs from the pharynx to the stomach

estrogens

class of predominantly female sex hormones important for the development and growth of the female reproductive tract, secondary sex characteristics, the female reproductive cycle, and the maintenance of pregnancy

excitable membrane

cell membrane that regulates the movement of ions so that an electrical signal can be generated

excitatory postsynaptic potential (EPSP)

graded potential in the postsynaptic membrane that is the result of depolarization and makes an action potential more likely to occur

exocrine gland

group of epithelial cells that secrete substances through ducts that open to the skin or to internal body surfaces that lead to the exterior of the body

exocrine system

cells, tissues, and organs that secrete substances directly to target tissues via glandular ducts

exogenous

describes substance made outside of the human body

external anal sphincter

voluntary skeletal muscle sphincter in the anal canal

external ear

structures on the lateral surface of the head, including the auricle and the ear canal back to the tympanic membrane

external urinary sphincter

skeletal muscle; must be relaxed consciously to void urine

exteroceptor

sensory receptor that is positioned to interpret stimuli from the external environment, such as photoreceptors in the eye or somatosensory receptors in the skin

extracellular fluid (ECF)

fluid exterior to cells; includes the interstitial fluid, blood plasma, and fluids found in other reservoirs in the body

extraocular muscle

one of six muscles originating out of the bones of the orbit and inserting into the surface of the eye which are responsible for moving the eye

extraocular muscles

six skeletal muscles that control eye movement within the orbit

FADH₂

high-energy molecule needed for glycolysis

facial nerve

seventh cranial nerve; responsible for contraction of the facial muscles and for part of the sense of taste, as well as causing saliva production

fascicle

small bundles of nerve or muscle fibers enclosed by connective tissue

fatty acid oxidation

breakdown of fatty acids into smaller chain fatty acids and acetyl CoA

fauces

opening between the oral cavity and the oropharynx

feces

semisolid waste product of digestion

femoral nerve

systemic nerve of the anterior leg that arises from the lumbar plexus

fenestrations

small windows through a cell, allowing rapid filtration based on size; formed in such a way as to allow substances to cross through a cell without mixing with cell contents

fertilization

unification of genetic material from male and female haploid gametes

fertilization membrane

impenetrable barrier that coats a nascent zygote; part of the slow block to polyspermy

fetus

developing human during the time from the end of the embryonic period (week 9) to birth

fibrous tunic

outer layer of the eye primarily composed of connective tissue known as the sclera and cornea

fibular nerve

systemic nerve of the posterior leg that begins as part of the sciatic nerve

fight-or-flight response

set of responses induced by sympathetic activity that lead to either fleeing a threat or standing up to it, which in the modern world is often associated with anxious feelings

filtration slits

formed by pedicels of podocytes; substances filter between the pedicels based on size

fimbriae

fingerlike projections on the distal uterine tubes

first messenger

hormone that binds to a cell membrane hormone receptor and triggers activation of a second messenger system

flatus

gas in the intestine

flavin adenine dinucleotide (FAD)

coenzyme used to produce FADH₂

fluid compartment

fluid inside all cells of the body constitutes a compartment system that is largely segregated from other systems

follicle

ovarian structure of one oocyte and surrounding granulosa (and later theca) cells

follicle-stimulating hormone (FSH)

anterior pituitary hormone that stimulates the production and maturation of sex cells

folliculogenesis

development of ovarian follicles from primordial to tertiary under the stimulation of gonadotropins

foramen magnum

large opening in the occipital bone of the skull through which the spinal cord emerges and the vertebral arteries enter the cranium

foramen ovale

shunt that directly connects the right and left atria and helps divert oxygenated blood from the fetal pulmonary circuit

forming urine

filtrate undergoing modifications through secretion and reabsorption before true urine is produced

fourth ventricle

the portion of the ventricular system that is in the region of the brain stem and opens into the subarachnoid space through the median and lateral apertures

fovea

exact center of the retina at which visual stimuli are focused for maximal acuity, where the retina is thinnest, at which there is nothing but photoreceptors

free nerve ending

configuration of a sensory receptor neuron with dendrites in the connective tissue of the organ, such as in the dermis of the skin, that are most often sensitive to chemical, thermal, and mechanical stimuli

frontal eye field

region of the frontal lobe associated with motor commands to orient the eyes toward an object of visual attention

frontal lobe

region of the cerebral cortex directly beneath the frontal bone of the cranium

functional group

group of atoms linked by strong covalent bonds that tends to behave as a distinct unit in chemical reactions with other atoms

fundus

dome-shaped region of the stomach above and to the left of the cardia

fundus

(of the uterus) domed portion of the uterus that is superior to the uterine tubes

gallbladder

accessory digestive organ that stores and concentrates bile

gamete

haploid reproductive cell that contributes genetic material to form an offspring

ganglion

localized collection of neuron cell bodies in the peripheral nervous system

ganglionic neuron

specifically refers to the cell body of a neuron in the autonomic system that is located in a ganglion

gap junction

allows cytoplasmic communications to occur between cells

gastric emptying

process by which mixing waves gradually cause the release of chyme into the duodenum

gastric gland

gland in the stomach mucosal epithelium that produces gastric juice

gastric phase

phase of gastric secretion that begins when food enters the stomach

gastric plexuses

neuronal networks in the wall of the stomach that are part of the enteric nervous system

gastric pit

narrow channel formed by the epithelial lining of the stomach mucosa

gastrin

peptide hormone that stimulates secretion of hydrochloric acid and gut motility

gastrocolic reflex

propulsive movement in the colon activated by the presence of food in the stomach

gastroileal reflex

long reflex that increases the strength of segmentation in the ileum

gastrulation

process of cell migration and differentiation into three primary germ layers following cleavage and implantation

gated

property of a channel that determines how it opens under specific conditions, such as voltage change or physical deformation

G cell

gastrin-secreting enteroendocrine cell

general adaptation syndrome (GAS)

the human body’s three-stage response pattern to short- and long-term stress

general sense

any sensory system that is distributed throughout the body and incorporated into organs of multiple other systems, such as the walls of the digestive organs or the skin

generator potential

graded potential from dendrites of a unipolar cell which generates the action potential in the initial segment of that cell’s axon

genotype

complete genetic makeup of an individual

gestation

in human development, the period required for embryonic and fetal development in utero; pregnancy

gigantism

disorder in children caused when abnormally high levels of GH prompt excessive growth

gingiva

gum

glans penis

bulbous end of the penis that contains a large number of nerve endings

glial cell

one of the various types of neural tissue cells responsible for maintenance of the tissue, and largely responsible for supporting neurons

globus pallidus

nuclei deep in the cerebrum that are part of the basal nuclei and can be divided into the internal and external segments

glomerular filtration rate (GFR)

rate of renal filtration

glomerulus

tuft of capillaries surrounded by Bowman’s capsule; filters the blood based on size

glossopharyngeal nerve

ninth cranial nerve; responsible for contraction of muscles in the tongue and throat and for part of the sense of taste, as well as causing saliva production

glucagon

pancreatic hormone that stimulates the catabolism of glycogen to glucose, thereby increasing blood glucose levels

glucocorticoids

hormones produced by the zona fasciculata of the adrenal cortex that influence glucose metabolism

glucokinase

cellular enzyme, found in the liver, which converts glucose into glucose-6-phosphate upon uptake into the cell

gluconeogenesis

process of glucose synthesis from pyruvate or other molecules

glucose-6-phosphate

phosphorylated glucose produced in the first step of glycolysis

glycogen

form that glucose assumes when it is stored

glycolysis

series of metabolic reactions that breaks down glucose into pyruvate and produces ATP

glycosuria

presence of glucose in the urine; caused by high blood glucose levels that exceed the ability of the kidneys to reabsorb the glucose; usually the result of untreated or poorly controlled diabetes mellitus

goblet cell

unicellular gland found in columnar epithelium that secretes mucous

goiter

enlargement of the thyroid gland either as a result of iodine deficiency or hyperthyroidism

gonadotropin-releasing hormone (GnRH)

hormone released by the hypothalamus that regulates the production of follicle-stimulating hormone and luteinizing hormone from the pituitary gland

gonadotropins

hormones that regulate the function of the gonads

gonads

reproductive organs (testes in men and ovaries in women) that produce gametes and reproductive hormones

G protein

guanosine triphosphate (GTP) hydrolase that physically moves from the receptor protein to the effector protein to activate the latter

G protein

protein associated with a cell membrane hormone receptor that initiates the next step in a second messenger system upon activation by hormone–receptor binding

G protein–coupled receptor

membrane protein complex that consists of a receptor protein that binds to a signaling molecule—a G protein—that is activated by that binding and in turn activates an effector protein (enzyme) that creates a second-messenger molecule in the cytoplasm of the target cell

graded potential

change in the membrane potential that varies in size, depending on the size of the stimulus that elicits it

granulosa cells

supportive cells in the ovarian follicle that produce estrogen

gray matter

regions of the nervous system containing cell bodies of neurons with few or no myelinated axons; actually may be more pink or tan in color, but called gray in contrast to white matter

gray rami communicantes

(singular = ramus communicans) unmyelinated structures that provide a short connection from a sympathetic chain ganglion to the spinal nerve that contains the postganglionic sympathetic fiber

greater splanchnic nerve

nerve that contains fibers of the central sympathetic neurons that do not synapse in the chain ganglia but project onto the celiac ganglion

growth hormone (GH)

anterior pituitary hormone that promotes tissue building and influences nutrient metabolism (also called somatotropin)

gustation

sense of taste

gustatory receptor cells

sensory cells in the taste bud that transduce the chemical stimuli of gustation

gyrus

ridge formed by convolutions on the surface of the cerebrum or cerebellum

G₀ phase

phase of the cell cycle, usually entered from the G₁ phase; characterized by long or permanent periods where the cell does not move forward into the DNA synthesis phase

G₁ phase

first phase of the cell cycle, after a new cell is born

G₂ phase

third phase of the cell cycle, after the DNA synthesis phase

hair cells

mechanoreceptor cells found in the inner ear that transduce stimuli for the senses of hearing and balance

haustrum

small pouch in the colon created by tonic contractions of teniae coli

haustral contraction

slow segmentation in the large intestine

hepatic artery

artery that supplies oxygenated blood to the liver

hepatic lobule

hexagonal-shaped structure composed of hepatocytes that radiate outward from a central vein

hepatic portal vein

vein that supplies deoxygenated nutrient-rich blood to the liver

hepatic sinusoid

blood capillaries between rows of hepatocytes that receive blood from the hepatic portal vein and the branches of the hepatic artery

hepatic vein

vein that drains into the inferior vena cava

hepatocytes

major functional cells of the liver

hepatopancreatic ampulla

(also, ampulla of Vater) bulb-like point in the wall of the duodenum where the bile duct and main pancreatic duct unite

hepatopancreatic sphincter

(also, sphincter of Oddi) sphincter regulating the flow of bile and pancreatic juice into the duodenum

heterozygous

having two different alleles for a given gene

hexokinase

cellular enzyme, found in most tissues, that converts glucose into glucose-6-phosphate upon uptake into the cell

hippocampus

gray matter deep in the temporal lobe that is very important for long-term memory formation

holocrine secretion

release of a substance caused by the rupture of a gland cell, which becomes part of the secretion

homologous

describes two copies of the same chromosome (not identical), one inherited from each parent

homozygous

having two identical alleles for a given gene

hormone

secretion of an endocrine organ that travels via the bloodstream or lymphatics to induce a response in target cells or tissues in another part of the body

hormone receptor

protein within a cell or on the cell membrane that binds a hormone, initiating the target cell response

human chorionic gonadotropin (hCG)

hormone that directs the corpus luteum to survive, enlarge, and continue producing progesterone and estrogen to suppress menses and secure an environment suitable for the developing embryo

hydrochloric acid (HCl)

digestive acid secreted by parietal cells in the stomach

hydrogen bond

dipole-dipole bond in which a hydrogen atom covalently bonded to an electronegative atom is weakly attracted to a second electronegative atom

hypoblast

lower layer of cells of the embryonic disc that extend into the blastocoel to form the yolk sac

hydrostatic pressure

pressure exerted by a fluid against a wall, caused by its own weight or pumping force

hydroxymethylglutaryl CoA (HMG CoA)

molecule created in the first step of the creation of ketone bodies from acetyl CoA

hymen

membrane that covers part of the opening of the vagina

hypercalcemia

abnormally increased blood levels of calcium

hypercapnia

abnormally elevated blood levels of CO₂

hyperchloremia

higher-than-normal blood chloride levels

hyperglycemia

abnormally high blood glucose levels

hyperkalemia

higher-than-normal blood potassium levels

hypernatremia

abnormal increase in blood sodium levels

hyperphosphatemia

abnormally increased blood phosphate levels

hyperthyroidism

clinically abnormal, elevated level of thyroid hormone in the blood; characterized by an increased metabolic rate, excess body heat, sweating, diarrhea, weight loss, and increased heart rate

hyperparathyroidism

disorder caused by overproduction of PTH that results in abnormally elevated blood calcium

hypocalcemia

abnormally low blood levels of calcium

hypocapnia

abnormally low blood levels of CO₂

hypochloremia

lower-than-normal blood chloride levels

hypoglossal nerve

twelfth cranial nerve; responsible for contraction of muscles of the tongue

hypokalemia

abnormally decreased blood levels of potassium

hyponatremia

lower-than-normal levels of sodium in the blood

hypoparathyroidism

disorder caused by underproduction of PTH that results in abnormally low blood calcium

hypophosphatemia

abnormally low blood phosphate levels

hypophyseal portal system

network of blood vessels that enables hypothalamic hormones to travel into the anterior lobe of the pituitary without entering the systemic circulation

hypothalamus

region of the diencephalon inferior to the thalamus that functions in neural and endocrine signaling

hypothalamus

major region of the diencephalon that is responsible for coordinating autonomic and endocrine control of homeostasis

hypothyroidism

clinically abnormal, low level of thyroid hormone in the blood; characterized by low metabolic rate, weight gain, cold extremities, constipation, and reduced mental activity

ileocecal sphincter

sphincter located where the small intestine joins with the large intestine

ileum

end of the small intestine between the jejunum and the large intestine

implantation

process by which a blastocyst embeds itself in the uterine endometrium

inactivation gate

part of a voltage-gated Na⁺ channel that closes when the membrane potential reaches +30 mV

inactive proenzymes

forms in which proteases are stored and released to prevent the inappropriate digestion of the native proteins of the stomach, pancreas, and small intestine

incomplete dominance

pattern of inheritance in which a heterozygous genotype expresses a phenotype intermediate between dominant and recessive phenotypes

incontinence

loss of ability to control micturition

incus

(also, anvil) ossicle of the middle ear that connects the malleus to the stapes

indirect pathway

connections within the basal nuclei from the striatum through the globus pallidus external segment and subthalamic nucleus to the globus pallidus internal segment/substantia nigra pars compacta that result in inhibition of the thalamus to decrease cortical control of movement

inferior colliculus

half of the midbrain tectum that is part of the brain stem auditory pathway

inferior mesenteric ganglion

one of the collateral ganglia of the sympathetic system that projects to the digestive system

inferior oblique

extraocular muscle responsible for lateral rotation of the eye

inferior rectus

extraocular muscle responsible for looking down

inferior olive

nucleus in the medulla that is involved in processing information related to motor control

infundibulum

stalk containing vasculature and neural tissue that connects the pituitary gland to the hypothalamus (also called the pituitary stalk)

infundibulum

(of the uterine tube) wide, distal portion of the uterine tube terminating in fimbriae

ingestion

taking food into the GI tract through the mouth

inguinal canal

opening in abdominal wall that connects the testes to the abdominal cavity

inhibin

hormone secreted by the male and female gonads that inhibits FSH production by the anterior pituitary

inhibitory postsynaptic potential (IPSP)

graded potential in the postsynaptic membrane that is the result of hyperpolarization and makes an action potential less likely to occur

interphase

entire life cycle of a cell, excluding mitosis

initial segment

first part of the axon as it emerges from the axon hillock, where the electrical signals known as action potentials are generated

inner cell mass

cluster of cells within the blastocyst that is fated to become the embryo

inner ear

structure within the temporal bone that contains the sensory apparati of hearing and balance

inner segment

in the eye, the section of a photoreceptor that contains the nucleus and other major organelles for normal cellular functions

inner synaptic layer

layer in the retina where bipolar cells connect to RGCs

inorganic compound

substance that does not contain both carbon and hydrogen

inositol triphosphate (IP₃)

molecule that initiates the release of calcium ions from intracellular stores

incisor

midline, chisel-shaped tooth used for cutting into food

insulin

pancreatic hormone that enhances the cellular uptake and utilization of glucose, thereby decreasing blood glucose levels

insulin

hormone secreted by the pancreas that stimulates the uptake of glucose into the cells

insulin-like growth factors (IGF)

protein that enhances cellular proliferation, inhibits apoptosis, and stimulates the cellular uptake of amino acids for protein synthesis

integration

nervous system function that combines sensory perceptions and higher cognitive functions (memories, learning, emotion, etc.) to produce a response

intercalated cell

specialized cell of the collecting ducts that secrete or absorb acid or bicarbonate; important in acid–base balance

intercostal nerve

systemic nerve in the thoracic cavity that is found between two ribs

internal anal sphincter

involuntary smooth muscle sphincter in the anal canal

internal carotid artery

branch from the common carotid artery that enters the cranium and supplies blood to the brain

internal urinary sphincter

smooth muscle at the juncture of the bladder and urethra; relaxes as the bladder fills to allow urine into the urethra

interoceptor

sensory receptor that is positioned to interpret stimuli from internal organs, such as stretch receptors in the wall of blood vessels

interventricular foramina

openings between the lateral ventricles and third ventricle allowing for the passage of CSF

intestinal gland

(also, crypt of Lieberkühn) gland in the small intestinal mucosa that secretes intestinal juice

intestinal juice

mixture of water and mucus that helps absorb nutrients from chyme

interstitial fluid (IF)

fluid in the small spaces between cells not contained within blood vessels

intracellular fluid (ICF)

fluid in the cytosol of cells

intramural ganglia

terminal ganglia of the parasympathetic system that are found within the walls of the target effector

intrinsic factor

glycoprotein required for vitamin B₁₂ absorption in the small intestine

intestinal phase

phase of gastric secretion that begins when chyme enters the intestine

inulin

plant polysaccharide injected to determine GFR; is neither secreted nor absorbed by the kidney, so its appearance in the urine is directly proportional to its filtration rate

ion

atom with an overall positive or negative charge

ionic bond

attraction between an anion and a cation

ionotropic receptor

neurotransmitter receptor that acts as an ion channel gate, and opens by the binding of the neurotransmitter

ipsilateral

word meaning on the same side, as in axons that do not cross the midline in a fiber tract

iris

colored portion of the anterior eye that surrounds the pupil

isthmus

narrow, medial portion of the uterine tube that joins the uterus

jejunum

middle part of the small intestine between the duodenum and the ileum

jugular veins

blood vessels that return “used” blood from the head and neck

juxtamedullary nephrons

nephrons adjacent to the border of the cortex and medulla with loops of Henle that extend into the renal medulla

juxtaglomerular apparatus (JGA)

located at the juncture of the DCT and the afferent and efferent arterioles of the glomerulus; plays a role in the regulation of renal blood flow and GFR

juxtaglomerular cell

modified smooth muscle cells of the afferent arteriole; secretes renin in response to a drop in blood pressure

karyotype

systematic arrangement of images of chromosomes into homologous pairs

ketone bodies

alternative source of energy when glucose is limited, created when too much acetyl CoA is created during fatty acid oxidation

kinesthesia

general sensory perception of movement of the body

kinesthesia

sense of body movement based on sensations in skeletal muscles, tendons, joints, and the skin

kinetochore

region of a centromere where microtubules attach to a pair of sister chromatids

Krebs cycle

also called the citric acid cycle or the tricarboxylic acid cycle, converts pyruvate into CO₂ and high-energy FADH₂, NADH, and ATP molecules

labium

lip

labial frenulum

midline mucous membrane fold that attaches the inner surface of the lips to the gums

labia majora

hair-covered folds of skin located behind the mons pubis

labia minora

thin, pigmented, hairless flaps of skin located medial and deep to the labia majora

lacrimal duct

duct in the medial corner of the orbit that drains tears into the nasal cavity

lacrimal gland

gland lateral to the orbit that produces tears to wash across the surface of the eye

lactase

brush border enzyme that breaks down lactose into glucose and galactose

lacteal

lymphatic capillary in the villi

lactiferous ducts

ducts that connect the mammary glands to the nipple and allow for the transport of milk

lactiferous sinus

area of milk collection between alveoli and lactiferous duct

lanugo

silk-like hairs that coat the fetus; shed later in fetal development

large intestine

terminal portion of the alimentary canal

lateral horn

region of the spinal cord gray matter in the thoracic, upper lumbar, and sacral regions that is the central component of the sympathetic division of the autonomic nervous system

lateral apertures

pair of openings from the fourth ventricle to the subarachnoid space on either side and between the medulla and cerebellum

lateral column

white matter of the spinal cord between the posterior horn on one side and the axons from the anterior horn on the same side; composed of many different groups of axons, of both ascending and descending tracts, carrying motor commands to and from the brain

lateral rectus

extraocular muscle responsible for abduction of the eye

lateral sulcus

surface landmark of the cerebral cortex that marks the boundary between the temporal lobe and the frontal and parietal lobes

lateral ventricles

portions of the ventricular system that are in the region of the cerebrum

laryngopharynx

part of the pharynx that functions in respiration and digestion

leakage channel

ion channel that opens randomly and is not gated to a specific event, also known as a non-gated channel

leaky tight junctions

tight junctions in which the sealing strands of proteins between the membranes of adjacent cells are fewer in number and incomplete; allows limited intercellular movement of solvent and solutes

left colic flexure

(also, splenic flexure) point where the transverse colon curves below the inferior end of the spleen

lens

component of the eye that focuses light on the retina

leptin

protein hormone secreted by adipose tissues in response to food consumption that promotes satiety

lesser splanchnic nerve

nerve that contains fibers of the central sympathetic neurons that do not synapse in the chain ganglia but project onto the inferior mesenteric ganglion

leukocyte esterase

enzyme produced by leukocytes that can be detected in the urine and that serves as an indirect indicator of urinary tract infection

levator palpebrae superioris

muscle that causes elevation of the upper eyelid, controlled by fibers in the oculomotor nerve

Leydig cells

cells between the seminiferous tubules of the testes that produce testosterone; a type of interstitial cell

ligand-gated cation channel

ion channel, such as the nicotinic receptor, that is specific to positively charged ions and opens when a molecule such as a neurotransmitter binds to it

ligand-gated channels

another name for an ionotropic receptor for which a neurotransmitter is the ligand

limbic cortex

collection of structures of the cerebral cortex that are involved in emotion, memory, and behavior and are part of the larger limbic system

limbic system

structures at the edge (limit) of the boundary between the forebrain and hindbrain that are most associated with emotional behavior and memory formation

lingual frenulum

mucous membrane fold that attaches the bottom of the tongue to the floor of the mouth

lingual lipase

digestive enzyme from glands in the tongue that acts on triglycerides

lipid

class of nonpolar organic compounds built from hydrocarbons and distinguished by the fact that they are not soluble in water

lipogenesis

synthesis of lipids that occurs in the liver or adipose tissues

lipolysis

breakdown of triglycerides into glycerol and fatty acids

lipoprotein lipase

enzyme that breaks down triglycerides in chylomicrons into fatty acids and monoglycerides

liver

largest gland in the body whose main digestive function is the production of bile

longitudinal fissure

large separation along the midline between the two cerebral hemispheres

loop of Henle

descending and ascending portions between the proximal and distal convoluted tubules; those of cortical nephrons do not extend into the medulla, whereas those of juxtamedullary nephrons do extend into the medulla

lower esophageal sphincter

smooth muscle sphincter that regulates food movement from the esophagus to the stomach

lower motor neuron

second neuron in the motor command pathway that is directly connected to the skeletal muscle

lumbar plexus

nerve plexus associated with the lumbar spinal nerves

lumbar puncture

procedure used to withdraw CSF from the lower lumbar region of the vertebral column that avoids the risk of damaging CNS tissue because the spinal cord ends at the upper lumbar vertebrae

luteinizing hormone (LH)

anterior pituitary hormone that triggers ovulation and the production of ovarian hormones in females, and the production of testosterone in males

macromolecule

large molecule formed by covalent bonding

macula

enlargement at the base of a semicircular canal at which transduction of equilibrium stimuli takes place within the ampulla

macula densa

cells found in the part of the DCT forming the JGA; sense Na⁺ concentration in the forming urine

main pancreatic duct

(also, duct of Wirsung) duct through which pancreatic juice drains from the pancreas

major duodenal papilla

point at which the hepatopancreatic ampulla opens into the duodenum

malleus

(also, hammer) ossicle that is directly attached to the tympanic membrane

maltase

brush border enzyme that breaks down maltose and maltotriose into two and three molecules of glucose, respectively

mammary glands

glands inside the breast that secrete milk

mass movement

long, slow, peristaltic wave in the large intestine

mastication

chewing

mechanical digestion

chewing, mixing, and segmentation that prepares food for chemical digestion

mechanoreceptor

receptor cell that transduces mechanical stimuli into an electrochemical signal

mechanically gated channel

ion channel that opens when a physical event directly affects the structure of the protein

meconium

fetal wastes consisting of ingested amniotic fluid, cellular debris, mucus, and bile

medial rectus

extraocular muscle responsible for adduction of the eye

median aperture

singular opening from the fourth ventricle into the subarachnoid space at the midline between the medulla and cerebellum

median nerve

systemic nerve of the arm, located between the ulnar and radial nerves

medulla

inner region of kidney containing the renal pyramids

meninges

protective outer coverings of the CNS composed of connective tissue

mesangial

contractile cells found in the glomerulus; can contract or relax to regulate filtration rate

mesenteric plexus

nervous tissue within the wall of the digestive tract that contains neurons that are the targets of autonomic preganglionic fibers and that project to the smooth muscle and glandular tissues in the digestive organ

menses

shedding of the inner portion of the endometrium out though the vagina; also referred to as menstruation

menses phase

phase of the menstrual cycle in which the endometrial lining is shed

menstrual cycle

approximately 28-day cycle of changes in the uterus consisting of a menses phase, a proliferative phase, and a secretory phase

merocrine secretion

release of a substance from a gland via exocytosis

mesoappendix

mesentery of the appendix

mesoderm

primary germ layer that becomes the skeleton, muscles, connective tissue, heart, blood vessels, and kidneys

mesothelium

simple squamous epithelial tissue which covers the major body cavities and is the epithelial portion of serous membranes

metabolic acidosis

condition wherein a deficiency of bicarbonate causes the blood to be overly acidic

metabolic alkalosis

condition wherein an excess of bicarbonate causes the blood to be overly alkaline

metabolism

sum of all catabolic and anabolic reactions that take place in the body

metabotropic receptor

neurotransmitter receptor that involves a complex of proteins that cause metabolic changes in a cell

metaphase

second stage of mitosis (and meiosis), characterized by the linear alignment of sister chromatids in the center of the cell

metaphase plate

linear alignment of sister chromatids in the center of the cell, which takes place during metaphase

micelle

tiny lipid-transport compound composed of bile salts and phospholipids with a fatty acid and monoacylglyceride core

micturition

also called urination or voiding

microglia

glial cell type in the CNS that serves as the resident component of the immune system

microvillus

small projection of the plasma membrane of the absorptive cells of the small intestinal mucosa

middle ear

space within the temporal bone between the ear canal and bony labyrinth where the ossicles amplify sound waves from the tympanic membrane to the oval window

migrating motility complex

form of peristalsis in the small intestine

mineralocorticoids

hormones produced by the zona glomerulosa cells of the adrenal cortex that influence fluid and electrolyte balance

minerals

inorganic compounds required by the body to ensure proper function of the body

mitosis

division of genetic material, during which the cell nucleus breaks down and two new, fully functional, nuclei are formed

mitotic phase

phase of the cell cycle in which a cell undergoes mitosis

mitotic spindle

network of microtubules, originating from centrioles, that arranges and pulls apart chromosomes during mitosis

mixing wave

unique type of peristalsis that occurs in the stomach

monoglyceride molecules

lipid consisting of a single fatty acid chain attached to a glycerol backbone

monosaccharide

monomer of carbohydrate; also known as a simple sugar

molar

tooth used for crushing and grinding food

molecule

two or more atoms covalently bonded together

monosaccharide

smallest, monomeric sugar molecule

mons pubis

mound of fatty tissue located at the front of the vulva

morula

tightly packed sphere of blastomeres that has reached the uterus but has not yet implanted itself

motilin

hormone that initiates migrating motility complexes

motility

movement of food through the GI tract

mucosa

innermost lining of the alimentary canal

mucosal barrier

protective barrier that prevents gastric juice from destroying the stomach itself

mucous gland

group of cells that secrete mucous, a thick, slippery substance that keeps tissues moist and acts as a lubricant

mucous neck cell

gastric gland cell that secretes a uniquely acidic mucus

multipolar

shape of a neuron that has multiple processes—the axon and two or more dendrites

muscularis

muscle (skeletal or smooth) layer of the alimentary canal wall

muscarinic receptor

type of acetylcholine receptor protein that is characterized by also binding to muscarine and is a metabotropic receptor

muscarinic receptor

type of acetylcholine receptor protein that is characterized by also binding to muscarine and is a metabotropic receptor

mutation

change in the nucleotide sequence of DNA

myelin

lipid-rich insulating substance surrounding the axons of many neurons, allowing for faster transmission of electrical signals

myelin sheath

lipid-rich layer of insulation that surrounds an axon, formed by oligodendrocytes in the CNS and Schwann cells in the PNS; facilitates the transmission of electrical signals

myenteric plexus

(plexus of Auerbach) major nerve supply to alimentary canal wall; controls motility

myometrium

smooth muscle layer of uterus that allows for uterine contractions during labor and expulsion of menstrual blood

NADH

high-energy molecule needed for glycolysis

neonatal hypothyroidism

condition characterized by cognitive deficits, short stature, and other signs and symptoms in people born to women who were iodine-deficient during pregnancy

nephrons

functional units of the kidney that carry out all filtration and modification to produce urine; consist of renal corpuscles, proximal and distal convoluted tubules, and descending and ascending loops of Henle; drain into collecting ducts

nerve

cord-like bundle of axons located in the peripheral nervous system that transmits sensory input and response output to and from the central nervous system

nerve plexus

network of nerves without neuronal cell bodies included

neural plate

thickened layer of neuroepithelium that runs longitudinally along the dorsal surface of an embryo and gives rise to nervous system tissue

neural fold

elevated edge of the neural groove

neural tube

precursor to structures of the central nervous system, formed by the invagination and separation of neuroepithelium

neural tunic
layer of the eye that contains nervous tissue, namely the retina

neuropeptide
neurotransmitter type that includes protein molecules and shorter chains of amino acids

neuron
neural tissue cell that is primarily responsible for generating and propagating electrical signals into, within, and out of the nervous system

neurotransmitter

chemical signal that is released from the synaptic end bulb of a neuron to cause a change in the target cell

neurulation

embryonic process that establishes the central nervous system

nicotinic receptor

type of acetylcholine receptor protein that is characterized by also binding to nicotine and is an ionotropic receptor

nicotinic receptor

type of acetylcholine receptor protein that is characterized by also binding to nicotine and is an ionotropic receptor

nicotinamide adenine dinucleotide (NAD)

coenzyme used to produce NADH

nociceptor

receptor cell that senses pain stimuli

node of Ranvier

gap between two myelinated regions of an axon, allowing for strengthening of the electrical signal as it propagates down the axon

nonspecific channel

channel that is not specific to one ion over another, such as a nonspecific cation channel that allows any positively charged ion across the membrane

norepinephrine

signaling molecule released as a neurotransmitter by most postganglionic sympathetic fibers as part of the sympathetic response, or as a hormone into the bloodstream from the adrenal medulla

norepinephrine

secondary catecholamine hormone secreted by the adrenal medulla in response to short-term stress; also called noradrenaline

notochord

rod-shaped, mesoderm-derived structure that provides support for growing fetus

nucleosidase

brush border enzyme that digests nucleotides

nucleotide

class of organic compounds composed of one or more phosphate groups, a pentose sugar, and a base

nucleus

in the nervous system, a localized collection of neuron cell bodies that are functionally related; a “center” of neural function

nucleus ambiguus

brain-stem nucleus that contains neurons that project through the vagus nerve to terminal ganglia in the thoracic cavity; specifically associated with the heart

occipital lobe

region of the cerebral cortex directly beneath the occipital bone of the cranium

occipital sinuses

dural sinuses along the edge of the occipital lobes of the cerebrum

oculomotor nerve

third cranial nerve; responsible for contraction of four of the extraocular muscles, the muscle in the upper eyelid, and pupillary constriction

odorant molecules

volatile chemicals that bind to receptor proteins in olfactory neurons to stimulate the sense of smell

olfaction

sense of smell

olfaction

special sense responsible for smell, which has a unique, direct connection to the cerebrum

olfactory bulb

central target of the first cranial nerve; located on the ventral surface of the frontal lobe in the cerebrum

olfactory epithelium

region of the nasal epithelium where olfactory neurons are located

olfactory nerve

first cranial nerve; responsible for the sense of smell

olfactory sensory neuron

receptor cell of the olfactory system, sensitive to the chemical stimuli of smell, the axons of which compose the first cranial nerve

oligodendrocyte

glial cell type in the CNS that provides the myelin insulation for axons in tracts

oliguria

below normal urine production of 400–500 mL/day

oocyte

cell that results from the division of the oogonium and undergoes meiosis I at the LH surge and meiosis II at fertilization to become a haploid ovum

oogenesis

process by which oogonia divide by mitosis to primary oocytes, which undergo meiosis to produce the secondary oocyte and, upon fertilization, the ovum

oogonia

ovarian stem cells that undergo mitosis during female fetal development to form primary oocytes

opsin

protein that contains the photosensitive cofactor retinal for phototransduction

optic disc

spot on the retina at which RGC axons leave the eye and blood vessels of the inner retina pass

optic nerve

second cranial nerve, which is responsible visual sensation

oral cavity

(also, buccal cavity) mouth

oral vestibule

part of the mouth bounded externally by the cheeks and lips, and internally by the gums and teeth

organ of Corti

structure in the cochlea in which hair cells transduce movements from sound waves into electrochemical signals

organic compound

substance that contains both carbon and hydrogen

organogenesis

development of the rudimentary structures of all of an embryo’s organs from the germ layers

oropharynx

part of the pharynx continuous with the oral cavity that functions in respiration and digestion

orthostatic reflex

sympathetic function that maintains blood pressure when standing to offset the increased effect of gravity

osmoreceptor

receptor cell that senses differences in the concentrations of bodily fluids on the basis of osmotic pressure

osmoreceptor

hypothalamic sensory receptor that is stimulated by changes in solute concentration (osmotic pressure) in the blood

ossicles

three small bones in the middle ear

otolith

layer of calcium carbonate crystals located on top of the otolithic membrane

otolithic membrane

gelatinous substance in the utricle and saccule of the inner ear that contains calcium carbonate crystals and into which the stereocilia of hair cells are embedded

outer segment

in the eye, the section of a photoreceptor that contains opsin molecules that transduce light stimuli

outer synaptic layer

layer in the retina at which photoreceptors connect to bipolar cells

oval window

membrane at the base of the cochlea where the stapes attaches, marking the beginning of the scala vestibuli

ovarian cycle

approximately 28-day cycle of changes in the ovary consisting of a follicular phase and a luteal phase

ovaries

female gonads that produce oocytes and sex steroid hormones (notably estrogen and progesterone)

ovulation

release of a secondary oocyte and associated granulosa cells from an ovary

ovum

haploid female gamete resulting from completion of meiosis II at fertilization

oxidation

loss of an electron

oxidation-reduction reaction

(also, redox reaction) pair of reactions in which an electron is passed from one molecule to another, oxidizing one and reducing the other

oxidative phosphorylation

process that converts high-energy NADH and FADH₂ into ATP

oxytocin

hypothalamic hormone stored in the posterior pituitary gland and important in stimulating uterine contractions in labor, milk ejection during breastfeeding, and feelings of attachment (also produced in males)

palatoglossal arch

muscular fold that extends from the lateral side of the soft palate to the base of the tongue

palatopharyngeal arch

muscular fold that extends from the lateral side of the soft palate to the side of the pharynx

palpebral conjunctiva

membrane attached to the inner surface of the eyelids that covers the anterior surface of the cornea

pancreas

organ with both exocrine and endocrine functions located posterior to the stomach that is important for digestion and the regulation of blood glucose

pancreas

accessory digestive organ that secretes pancreatic juice

pancreatic amylase

enzyme secreted by the pancreas that completes the chemical digestion of carbohydrates in the small intestine

pancreatic islets

specialized clusters of pancreatic cells that have endocrine functions; also called islets of Langerhans

pancreatic lipase

enzyme secreted by the pancreas that participates in lipid digestion

pancreatic lipases

enzymes released from the pancreas that digest lipids in the diet

pancreatic nuclease

enzyme secreted by the pancreas that participates in nucleic acid digestion

pancreatic juice

secretion of the pancreas containing digestive enzymes and bicarbonate

papilla

for gustation, a bump-like projection on the surface of the tongue that contains taste buds

paracrine

chemical signal that elicits a response in neighboring cells; also called paracrine factor

parasympathetic division

division of the autonomic nervous system responsible for restful and digestive functions

parathyroid glands

small, round glands embedded in the posterior thyroid gland that produce parathyroid hormone (PTH)

parathyroid hormone (PTH)

peptide hormone produced and secreted by the parathyroid glands in response to low blood calcium levels

paravertebral ganglia

autonomic ganglia superior to the sympathetic chain ganglia

parietal cell

gastric gland cell that secretes hydrochloric acid and intrinsic factor

parietal lobe

region of the cerebral cortex directly beneath the parietal bone of the cranium

parieto-occipital sulcus

groove in the cerebral cortex representing the border between the parietal and occipital cortices

parotid gland

one of a pair of major salivary glands located inferior and anterior to the ears

pectinate line

horizontal line that runs like a ring, perpendicular to the inferior margins of the anal sinuses

pedicels

finger-like projections of podocytes surrounding glomerular capillaries; interdigitate to form a filtration membrane

penis

male organ of copulation

pepsin

enzyme that begins to break down proteins in the stomach

pepsinogen

inactive form of pepsin

peptide bond

covalent bond formed by dehydration synthesis between two amino acids

perineurium

layer of connective tissue surrounding fascicles within a nerve

peripheral nervous system (PNS)

anatomical division of the nervous system that is largely outside the cranial and vertebral cavities, namely all parts except the brain and spinal cord

peristalsis

muscular contractions and relaxations that propel food through the GI tract

peritubular capillaries

second capillary bed of the renal portal system; surround the proximal and distal convoluted tubules; associated with the vasa recta

permanent tooth

one of 32 adult teeth

perimetrium

outer epithelial layer of uterine wall

pH

negative logarithm of the hydrogen ion (H⁺) concentration of a solution

pharynx

throat

phenotype

physical or biochemical manifestation of the genotype; expression of the alleles

phosphatase

brush border enzyme that digests nucleotides

phosphodiesterase (PDE)

cytosolic enzyme that deactivates and degrades cAMP

phospholipid

a lipid compound in which a phosphate group is combined with a diglyceride

phosphorylation

addition of one or more phosphate groups to an organic compound

phosphorylation cascade

signaling event in which multiple protein kinases phosphorylate the next protein substrate by transferring a phosphate group from ATP to the protein

photoisomerization

chemical change in the retinal molecule that alters the bonding so that it switches from the 11-cis-retinal isomer to the all-trans-retinal isomer

photon

individual “packet” of light

photoreceptor

receptor cell specialized to respond to light stimuli

phrenic nerve

systemic nerve from the cervical plexus that enervates the diaphragm

physiological sphincter

sphincter consisting of circular smooth muscle indistinguishable from adjacent muscle but possessing differential innervations, permitting its function as a sphincter; structurally weak

pia mater

thin, innermost membrane of the meninges that directly covers the surface of the CNS

pineal gland

endocrine gland that secretes melatonin, which is important in regulating the sleep-wake cycle

pinealocyte

cell of the pineal gland that produces and secretes the hormone melatonin

pituitary dwarfism

disorder in children caused when abnormally low levels of GH result in growth retardation

pituitary gland

bean-sized organ suspended from the hypothalamus that produces, stores, and secretes hormones in response to hypothalamic stimulation (also called hypophysis)

placenta

organ that forms during pregnancy to nourish the developing fetus; also regulates waste and gas exchange between mother and fetus

placenta previa

low placement of fetus within uterus causes placenta to partially or completely cover the opening of the cervix as it grows

placentation

formation of the placenta; complete by weeks 14–16 of pregnancy

plasma osmolality

ratio of solutes to a volume of solvent in the plasma; plasma osmolality reflects a person’s state of hydration

plexus

network of nerves or nervous tissue

podocytes

cells forming finger-like processes; form the visceral layer of Bowman’s capsule; pedicels of the podocytes interdigitate to form a filtration membrane

polar body

smaller cell produced during the process of meiosis in oogenesis

polar molecule

molecule with regions that have opposite charges resulting from uneven numbers of electrons in the nuclei of the atoms participating in the covalent bond

polysaccharide

compound consisting of more than two carbohydrate monomers bonded by dehydration synthesis via glycosidic bonds

polyspermy

penetration of an oocyte by more than one sperm

polysaccharides

complex carbohydrates made up of many monosaccharides

polyuria

urine production in excess of 2.5 L/day; may be caused by diabetes insipidus, diabetes mellitus, or excessive use of diuretics

porta hepatis

“gateway to the liver” where the hepatic artery and hepatic portal vein enter the liver

portal triad

bile duct, hepatic artery branch, and hepatic portal vein branch

postabsorptive state

also called the fasting state; the metabolic state occurring after digestion when food is no longer the body’s source of energy and it must rely on stored glycogen

postganglionic fiber

axon from a ganglionic neuron in the autonomic nervous system that projects to and synapses with the target effector; sometimes referred to as a postganglionic neuron

postsynaptic potential (PSP)

graded potential in the postsynaptic membrane caused by the binding of neurotransmitter to protein receptors

postcentral gyrus

ridge just posterior to the central sulcus, in the parietal lobe, where somatosensory processing initially takes place in the cerebrum

posterior columns

white matter of the spinal cord that lies between the posterior horns of the gray matter, sometimes referred to as the dorsal column; composed of axons of ascending tracts that carry sensory information up to the brain

posterior horn

gray matter region of the spinal cord in which sensory input arrives, sometimes referred to as the dorsal horn

posterior median sulcus

midline feature of the posterior spinal cord, marking the separation between right and left sides of the cord

posterolateral sulcus

feature of the posterior spinal cord marking the entry of posterior nerve roots and the separation between the posterior and lateral columns of the white matter

PP cell

minor cell type in the pancreas that secretes the hormone pancreatic polypeptide

precentral gyrus

primary motor cortex located in the frontal lobe of the cerebral cortex

precentral gyrus of the frontal cortex

region of the cerebral cortex responsible for generating motor commands, where the upper motor neuron cell body is located

prefrontal lobe

specific region of the frontal lobe anterior to the more specific motor function areas, which can be related to the early planning of movements and intentions to the point of being personality-type functions

preganglionic fiber

axon from a central neuron in the autonomic nervous system that projects to and synapses with a ganglionic neuron; sometimes referred to as a preganglionic neuron

prepuce

(also, foreskin) flap of skin that forms a collar around, and thus protects and lubricates, the glans penis; also referred as the foreskin

premolar

(also, bicuspid) transitional tooth used for mastication, crushing, and grinding food

premotor area

region of the frontal lobe responsible for planning movements that will be executed through the primary motor cortex

prevertebral ganglia

autonomic ganglia that are anterior to the vertebral column and functionally related to the sympathetic chain ganglia

primary follicles

ovarian follicles with a primary oocyte and one layer of cuboidal granulosa cells

primitive streak

indentation along the dorsal surface of the epiblast through which cells migrate to form the endoderm and mesoderm during gastrulation

primordial follicles

least developed ovarian follicles that consist of a single oocyte and a single layer of flat (squamous) granulosa cells

principal cell

found in collecting ducts and possess channels for the recovery or loss of sodium and potassium; under the control of aldosterone; also have aquaporin channels under ADH control to regulate recovery of water

process

in cells, an extension of a cell body; in the case of neurons, this includes the axon and dendrites

progesterone

predominantly female sex hormone important in regulating the female reproductive cycle and the maintenance of pregnancy

prolactin (PRL)

anterior pituitary hormone that promotes development of the mammary glands and the production of breast milk

proliferative phase

phase of the menstrual cycle in which the endometrium proliferates

propagation

movement of an action potential along the length of an axon

prophase

first stage of mitosis (and meiosis), characterized by breakdown of the nuclear envelope and condensing of the chromatin to form chromosomes

propulsion

voluntary process of swallowing and the involuntary process of peristalsis that moves food through the digestive tract

proprioception

general sensory perceptions providing information about location and movement of body parts; the “sense of the self”

proprioception

sense of position and movement of the body

proprioceptor

receptor cell that senses changes in the position and kinesthetic aspects of the body

prostaglandin

lipid compound derived from fatty acid chains and important in regulating several body processes

prostate gland

doughnut-shaped gland at the base of the bladder surrounding the urethra and contributing fluid to semen during ejaculation

protein

class of organic compounds that are composed of many amino acids linked together by peptide bonds

protein kinase

enzyme that initiates a phosphorylation cascade upon activation

proteolysis

process of breaking proteins into smaller peptides

proximal convoluted tubules (PCTs)

tortuous tubules receiving filtrate from Bowman’s capsule; most active part of the nephron in reabsorption and secretion

pseudostratified columnar epithelium

tissue that consists of a single layer of irregularly shaped and sized cells that give the appearance of multiple layers; found in ducts of certain glands and the upper respiratory tract

pulp cavity

deepest portion of a tooth, containing nerve endings and blood vessels

pupil

open hole at the center of the iris that light passes through into the eye

Punnett square

grid used to display all possible combinations of alleles transmitted by parents to offspring and predict the mathematical probability of offspring inheriting a given genotype

purine

nitrogen-containing base with a double ring structure; adenine and guanine

putamen

nucleus deep in the cerebrum that is part of the basal nuclei; along with the caudate, it is part of the striatum

pyloric antrum

wider, more superior part of the pylorus

pyloric canal

narrow, more inferior part of the pylorus

pyloric sphincter

sphincter that controls stomach emptying

pylorus

lower, funnel-shaped part of the stomach that is continuous with the duodenum

pyrimidine

nitrogen-containing base with a single ring structure; cytosine, thiamine, and uracil

pyruvate

three-carbon end product of glycolysis and starting material that is converted into acetyl CoA that enters the Krebs cycle

quickening

fetal movements that are strong enough to be felt by the mother

radial nerve

systemic nerve of the arm, the distal component of which is located near the radial bone

recessive

describes a trait that is only expressed in homozygous form and is masked in heterozygous form

recessive lethal

inheritance pattern in which individuals with two copies of a lethal allele do not survive in utero or have a shortened life span

receptor cell

cell that transduces environmental stimuli into neural signals

receptor potential

graded potential in a specialized sensory cell that directly causes the release of neurotransmitter without an intervening action potential

rectal valve

one of three transverse folds in the rectum where feces is separated from flatus

rectum

part of the large intestine between the sigmoid colon and anal canal

reduction

gaining of an electron

refractory period

time after the initiation of an action potential when another action potential cannot be generated

relative refractory period

time during the refractory period when a new action potential can only be initiated by a stronger stimulus than the current action potential because voltage-gated K⁺ channels are not closed

renal columns

extensions of the renal cortex into the renal medulla; separates the renal pyramids; contains blood vessels and connective tissues

renal corpuscle

consists of the glomerulus and Bowman’s capsule

renal cortex

outer part of kidney containing all of the nephrons; some nephrons have loops of Henle extending into the medulla

renal fat pad

adipose tissue between the renal fascia and the renal capsule that provides protective cushioning to the kidney

renal hilum

recessed medial area of the kidney through which the renal artery, renal vein, ureters, lymphatics, and nerves pass

renal papillae

medullary area of the renal pyramids where collecting ducts empty urine into the minor calyces

renal pyramids

six to eight cone-shaped tissues in the medulla of the kidney containing collecting ducts and the loops of Henle of juxtamedullary nephrons

renin

enzyme produced by juxtaglomerular cells in response to decreased blood pressure or sympathetic nervous activity; catalyzes the conversion of angiotensinogen into angiotensin I

repolarization

return of the membrane potential to its normally negative voltage at the end of the action potential

resistance

property of an axon that relates to the ability of particles to diffuse through the cytoplasm; this is inversely proportional to the fiber diameter

response

nervous system function that causes a target tissue (muscle or gland) to produce an event as a consequence to stimuli

rest and digest

set of functions associated with the parasympathetic system that lead to restful actions and digestion

resting membrane potential

the difference in voltage measured across a cell membrane under steady-state conditions, typically -70 mV

respiratory acidosis

condition wherein an excess of carbonic acid or CO₂ causes the blood to be overly acidic

respiratory alkalosis

condition wherein a deficiency of carbonic acid/CO₂ levels causes the blood to be overly alkaline

reticular formation

diffuse region of gray matter throughout the brain stem that regulates sleep, wakefulness, and states of consciousness

reticular lamina

matrix containing collagen and elastin secreted by connective tissue; a component of the basement membrane

reticuloendothelial cell

(also, Kupffer cell) phagocyte in hepatic sinusoids that filters out material from venous blood from the alimentary canal

retina

nervous tissue of the eye at which phototransduction takes place

retinal

cofactor in an opsin molecule that undergoes a biochemical change when struck by a photon (pronounced with a stress on the last syllable)

retinal ganglion cell (RGC)

neuron of the retina that projects along the second cranial nerve

retroperitoneal

located posterior to the peritoneum

retroperitoneal

outside the peritoneal cavity; in the case of the kidney and ureters, between the parietal peritoneum and the abdominal wall

ribonuclease

pancreatic enzyme that digests RNA

ribonucleic acid (RNA)

ribose-containing nucleotide that helps manifest the genetic code as protein

right colic flexure

(also, hepatic flexure) point, at the inferior surface of the liver, where the ascending colon turns abruptly to the left

rhodopsin

photopigment molecule found in the rod photoreceptors

rod photoreceptor

one of the two types of retinal receptor cell that is specialized for low-light vision

root

portion of a tooth embedded in the alveolar processes beneath the gum line

round window

membrane that marks the end of the scala tympani

ruga

fold of alimentary canal mucosa and submucosa in the empty stomach and other organs

rugae

(of the vagina) folds of skin in the vagina that allow it to stretch during intercourse and childbirth

saccharolytic fermentation

anaerobic decomposition of carbohydrates

saccule

structure of the inner ear responsible for transducing linear acceleration in the vertical plane

sacral micturition center

group of neurons in the sacral region of the spinal cord that controls urination; acts reflexively unless its action is modified by higher brain centers to allow voluntary urination

sacral plexus

nerve plexus associated with the lower lumbar and sacral spinal nerves

saliva

aqueous solution of proteins and ions secreted into the mouth by the salivary glands

salivary amylase

digestive enzyme in saliva that acts on starch

salivary amylase

digestive enzyme that is found in the saliva and begins the digestion of carbohydrates in the mouth

salivary gland

an exocrine gland that secretes a digestive fluid called saliva

salivation

secretion of saliva

saltatory conduction

quick propagation of the action potential along a myelinated axon owing to voltage-gated Na⁺ channels being present only at the nodes of Ranvier

satellite cell

glial cell type in the PNS that provides support for neurons in the ganglia

scala tympani

portion of the cochlea that extends from the apex to the round window

scala vestibuli

portion of the cochlea that extends from the oval window to the apex

Schwann cell

glial cell type in the PNS that provides the myelin insulation for axons in nerves

saphenous nerve

systemic nerve of the lower anterior leg that is a branch from the femoral nerve

sciatic nerve

systemic nerve from the sacral plexus that is a combination of the tibial and fibular nerves and extends across the hip joint and gluteal region into the upper posterior leg

sciatica

painful condition resulting from inflammation or compression of the sciatic nerve or any of the spinal nerves that contribute to it

sclera

white of the eye

scrotum

external pouch of skin and muscle that houses the testes

second messenger

molecule that initiates a signaling cascade in response to hormone binding on a cell membrane receptor and activation of a G protein

secondary follicles

ovarian follicles with a primary oocyte and multiple layers of granulosa cells

secretin

hormone released in the small intestine to aid in digestion

secretory phase

phase of the menstrual cycle in which the endometrium secretes a nutrient-rich fluid in preparation for implantation of an embryo

segmentation

alternating contractions and relaxations of non-adjacent segments of the intestine that move food forward and backward, breaking it apart and mixing it with digestive juices

semen

ejaculatory fluid composed of sperm and secretions from the seminal vesicles, prostate, and bulbourethral glands

semicircular canals

structures within the inner ear responsible for transducing rotational movement information

seminal vesicle

gland that produces seminal fluid, which contributes to semen

seminiferous tubules

tube structures within the testes where spermatogenesis occurs

sensation

nervous system function that receives information from the environment and translates it into the electrical signals of nervous tissue

sensory modality

a particular system for interpreting and perceiving environmental stimuli by the nervous system

serosa

outermost layer of the alimentary canal wall present in regions within the abdominal cavity

Sertoli cells

cells that support germ cells through the process of spermatogenesis; a type of sustentacular cell

serous gland

group of cells within the serous membrane that secrete a lubricating substance onto the surface

sex chromosomes

pair of chromosomes involved in sex determination; in males, the XY chromosomes; in females, the XX chromosomes

shunt

circulatory shortcut that diverts the flow of blood from one region to another

simple columnar epithelium

tissue that consists of a single layer of column-like cells; promotes secretion and absorption in tissues and organs

simple cuboidal epithelium

tissue that consists of a single layer of cube-shaped cells; promotes secretion and absorption in ducts and tubules

simple squamous epithelium

tissue that consists of a single layer of flat scale-like cells; promotes diffusion and filtration across surface

sigmoid colon

end portion of the colon, which terminates at the rectum

sigmoid sinuses

dural sinuses that drain directly into the jugular veins

sister chromatid

one of a pair of identical chromosomes, formed during DNA replication

size exclusion

principle of selectively allowing ions through a channel on the basis of their relative size

small intestine

section of the alimentary canal where most digestion and absorption occurs

sodium bicarbonate

anion released into the small intestine to neutralize the pH of the food from the stomach

soft palate

posterior region of the bottom portion of the nasal cavity that consists of skeletal muscle

solution

homogeneous liquid mixture in which a solute is dissolved into molecules within a solvent

soma

in neurons, that portion of the cell that contains the nucleus; the cell body, as opposed to the cell processes (axons and dendrites)

somatic cell

all cells of the body excluding gamete cells

somatic nervous system (SNS)

functional division of the nervous system that is concerned with conscious perception, voluntary movement, and skeletal muscle reflexes

somite

one of the paired, repeating blocks of tissue located on either side of the notochord in the early embryo

somatosensation

general senses related to the body, usually thought of as the senses of touch, which would include pain, temperature, and proprioception

somatosensation

general sense associated with modalities lumped together as touch

spatial summation

combination of graded potentials across the neuronal cell membrane caused by signals from separate presynaptic elements that add up to initiate an action potential

special sense

any sensory system associated with a specific organ structure, namely smell, taste, sight, hearing, and balance

specific gravity

weight of a liquid compared to pure water, which has a specific gravity of 1.0; any solute added to water will increase its specific gravity

sperm

(also, spermatozoon) male gamete

spermatic cord

bundle of nerves and blood vessels that supplies the testes; contains ductus deferens

spermatid

immature sperm cells produced by meiosis II of secondary spermatocytes

spermatocyte

cell that results from the division of spermatogonium and undergoes meiosis I and meiosis II to form spermatids

spermatogenesis

formation of new sperm, occurs in the seminiferous tubules of the testes

spermatogonia

(singular = spermatogonium) diploid precursor cells that become sperm

spermiogenesis

transformation of spermatids to spermatozoa during spermatogenesis

S phase

stage of the cell cycle during which DNA replication occurs

spinal cord

organ of the central nervous system found within the vertebral cavity and connected with the periphery through spinal nerves; mediates reflex behaviors

spinal accessory nerve

eleventh cranial nerve; responsible for contraction of neck muscles

spinal nerve

one of 31 nerves connected to the spinal cord

spiral ganglion

location of neuronal cell bodies that transmit auditory information along the eighth cranial nerve

stage of exhaustion

stage three of the general adaptation syndrome; the body’s long-term response to stress mediated by the hormones of the adrenal cortex

stage of resistance

stage two of the general adaptation syndrome; the body’s continued response to stress after stage one diminishes

stapes

(also, stirrup) ossicle of the middle ear that is attached to the inner ear

steroid

(also, sterol) lipid compound composed of four hydrocarbon rings bonded to a variety of other atoms and molecules

stereocilia

array of apical membrane extensions in a hair cell that transduce movements when they are bent

stimulus

an event in the external or internal environment that registers as activity in a sensory neuron

stomach

alimentary canal organ that contributes to chemical and mechanical digestion of food from the esophagus before releasing it, as chyme, to the small intestine

straight sinus

dural sinus that drains blood from the deep center of the brain to collect with the other sinuses

stratified columnar epithelium

tissue that consists of two or more layers of column-like cells, contains glands and is found in some ducts

stratified cuboidal epithelium

tissue that consists of two or more layers of cube-shaped cells, found in some ducts

stratified squamous epithelium

tissue that consists of multiple layers of cells with the most apical being flat scale-like cells; protects surfaces from abrasion

striatum

the caudate and putamen collectively, as part of the basal nuclei, which receive input from the cerebral cortex

subarachnoid space

space between the arachnoid mater and pia mater that contains CSF and the fibrous connections of the arachnoid trabeculae

subcortical nucleus

all the nuclei beneath the cerebral cortex, including the basal nuclei and the basal forebrain

sublingual gland

one of a pair of major salivary glands located beneath the tongue

submandibular gland

one of a pair of major salivary glands located in the floor of the mouth

submodality

specific sense within a broader major sense such as sweet as a part of the sense of taste, or color as a part of vision

submucosa

layer of dense connective tissue in the alimentary canal wall that binds the overlying mucosa to the underlying muscularis

submucosal plexus

(plexus of Meissner) nerve supply that regulates activity of glands and smooth muscle

substantia nigra pars compacta

nuclei within the basal nuclei that release dopamine to modulate the function of the striatum; part of the motor pathway

substantia nigra pars reticulata

nuclei within the basal nuclei that serve as an output center of the nuclei; part of the motor pathway

substrate

reactant in an enzymatic reaction

subthalamus

nucleus within the basal nuclei that is part of the indirect pathway

sucrase

brush border enzyme that breaks down sucrose into glucose and fructose

sulcus

groove formed by convolutions in the surface of the cerebral cortex

summate

to add together, as in the cumulative change in postsynaptic potentials toward reaching threshold in the membrane, either across a span of the membrane or over a certain amount of time

superior oblique

extraocular muscle responsible for medial rotation of the eye

superior rectus

extraocular muscle responsible for looking up

superior sagittal sinus

dural sinus that runs along the top of the longitudinal fissure and drains blood from the majority of the outer cerebrum

superior colliculus

half of the midbrain tectum that is responsible for aligning visual, auditory, and somatosensory spatial perceptions

superior cervical ganglion

one of the paravertebral ganglia of the sympathetic system that projects to the head

superior mesenteric ganglion

one of the collateral ganglia of the sympathetic system that projects to the digestive system

suspension

liquid mixture in which particles distributed in the liquid settle out over time

suspensory ligaments

bands of connective tissue that suspend the breast onto the chest wall by attachment to the overlying dermis

synaptic cleft

small gap between cells in a chemical synapse where neurotransmitter diffuses from the presynaptic element to the postsynaptic element

synaptic end bulb

swelling at the end of an axon where neurotransmitter molecules are released onto a target cell across a synapse

synapse

narrow junction across which a chemical signal passes from neuron to the next, initiating a new electrical signal in the target cell

sympathetic chain ganglia

series of ganglia adjacent to the vertebral column that receive input from central sympathetic neurons

sympathetic chain ganglia

autonomic ganglia in a chain along the anterolateral aspect of the vertebral column that are responsible for contributing to homeostatic mechanisms of the autonomic nervous system

sympathetic division
division of the autonomic nervous system associated with the fight-or-flight response

syncytiotrophoblast

superficial cells of the trophoblast that fuse to form a multinucleated body that digests endometrial cells to firmly secure the blastocyst to the uterine wall

systemic nerve

nerve in the periphery distal to a nerve plexus or spinal nerve

target effector

organ, tissue, or gland that will respond to the control of an autonomic or somatic or endocrine signal

taste buds

structures within a papilla on the tongue that contain gustatory receptor cells

tectorial membrane

component of the organ of Corti that lays over the hair cells, into which the stereocilia are embedded

tectum

region of the midbrain, thought of as the roof of the cerebral aqueduct, which is subdivided into the inferior and superior colliculi

tegmentum

region of the midbrain, thought of as the floor of the cerebral aqueduct, which continues into the pons and medulla as the floor of the fourth ventricle

telophase

final stage of mitosis (and meiosis), preceding cytokinesis, characterized by the formation of two new daughter nuclei

temporal lobe

region of the cerebral cortex directly beneath the temporal bone of the cranium

temporal summation

combination of graded potentials at the same location on a neuron resulting in a strong signal from one input

tenia coli

one of three smooth muscle bands that make up the longitudinal muscle layer of the muscularis in all of the large intestine except the terminal end

terminal electron acceptor

oxygen, the recipient of the free hydrogen at the end of the electron transport chain

terminal ganglia

ganglia of the parasympathetic division of the autonomic system, which are located near or within the target effector, the latter also known as intramural ganglia

terminal ganglion

autonomic ganglia that are near or within the walls of organs that are responsible for contributing to homeostatic mechanisms of the autonomic nervous system

tertiary follicles

(also, antral follicles) ovarian follicles with a primary or secondary oocyte, multiple layers of granulosa cells, and a fully formed antrum

testes

(singular = testis) male gonads

testosterone

steroid hormone secreted by the male testes and important in the maturation of sperm cells, growth and development of the male reproductive system, and the development of male secondary sex characteristics

thalamus

major region of the diencephalon that is responsible for relaying information between the cerebrum and the hindbrain, spinal cord, and periphery

thalamus

region of the central nervous system that acts as a relay for sensory pathways

theca cells

estrogen-producing cells in a maturing ovarian follicle

thermoreceptor

type of sensory receptor capable of transducing temperature stimuli into neural action potentials

thermoreceptor

sensory receptor specialized for temperature stimuli

third ventricle

portion of the ventricular system that is in the region of the diencephalon

thoracolumbar system

alternate name for the sympathetic division of the autonomic nervous system that is based on the anatomical location of central neurons in the lateral horn of the thoracic and upper lumbar spinal cord

threshold

membrane voltage at which an action potential is initiated

thymosins

hormones produced and secreted by the thymus that play an important role in the development and differentiation of T cells

thymus

organ that is involved in the development and maturation of T-cells and is particularly active during infancy and childhood

thyroid gland

large endocrine gland responsible for the synthesis of thyroid hormones

thyroid-stimulating hormone (TSH)

anterior pituitary hormone that triggers secretion of thyroid hormones by the thyroid gland (also called thyrotropin)

thyroxine

(also, tetraiodothyronine, T₄) amino acid–derived thyroid hormone that is more abundant but less potent than T₃ and often converted to T₃ by target cells

tibial nerve

systemic nerve of the posterior leg that begins as part of the sciatic nerve

tight junction

forms an impermeable barrier between cells

tongue

accessory digestive organ of the mouth, the bulk of which is composed of skeletal muscle

topographical

relating to positional information

tract

bundle of axons in the central nervous system having the same function and point of origin

trait

variation of an expressed characteristic

transamination

transfer of an amine group from one molecule to another as a way to turn nitrogen waste into ammonia so that it can enter the urea cycle

transduction

process of changing an environmental stimulus into the electrochemical signals of the nervous system

transitional epithelium

form of stratified epithelium found in the urinary tract, characterized by an apical layer of cells that change shape in response to the presence of urine

transverse colon

part of the colon between the ascending colon and the descending colon

transverse sinuses

dural sinuses that drain along either side of the occipital–cerebellar space

tricarboxylic acid cycle (TCA)

also called the Krebs cycle or the citric acid cycle; converts pyruvate into CO₂ and high-energy FADH₂, NADH, and ATP molecules

trigeminal ganglion

sensory ganglion that contributes sensory fibers to the trigeminal nerve

trigeminal nerve

fifth cranial nerve; responsible for cutaneous sensation of the face and contraction of the muscles of mastication

trigone

area at the base of the bladder marked by the two ureters in the posterior–lateral aspect and the urethral orifice in the anterior aspect oriented like points on a triangle

triglyceride

lipid compound composed of a glycerol molecule bonded with three fatty acid chains

triglycerides

lipids, or fats, consisting of three fatty acid chains attached to a glycerol backbone

triiodothyronine

(also, T₃) amino acid–derived thyroid hormone that is less abundant but more potent than T₄

trochlea

cartilaginous structure that acts like a pulley for the superior oblique muscle

trochlear nerve

fourth cranial nerve; responsible for contraction of one of the extraocular muscles

trophoblast

fluid-filled shell of squamous cells destined to become the chorionic villi, placenta, and associated fetal membranes

trypsin

pancreatic enzyme that activates chymotrypsin and digests protein

trypsinogen

proenzyme form of trypsin

tympanic membrane

ear drum

umami

taste submodality for sensitivity to the concentration of amino acids; also called the savory sense

umbilical cord

connection between the developing conceptus and the placenta; carries deoxygenated blood and wastes from the fetus and returns nutrients and oxygen from the mother

utricle

structure of the inner ear responsible for transducing linear acceleration in the horizontal plane

ulnar nerve

systemic nerve of the arm located close to the ulna, a bone of the forear

unipolar

shape of a neuron which has only one process that includes both the axon and dendrite

upper esophageal sphincter

skeletal muscle sphincter that regulates food movement from the pharynx to the esophagus

upper motor neuron

first neuron in the motor command pathway with its cell body in the cerebral cortex that synapses on the lower motor neuron in the spinal cord

upregulation

increase in the number of hormone receptors, typically in response to chronically reduced levels of a hormone

urea cycle

process that converts potentially toxic nitrogen waste into urea that can be eliminated through the kidneys

urethra

transports urine from the bladder to the outside environment

urinalysis

analysis of urine to diagnose disease

urochrome

heme-derived pigment that imparts the typical yellow color of urine

uterine tubes

(also, fallopian tubes or oviducts) ducts that facilitate transport of an ovulated oocyte to the uterus

uterus

muscular hollow organ in which a fertilized egg develops into a fetus

vagina

tunnel-like organ that provides access to the uterus for the insertion of semen and from the uterus for the birth of a baby

vagus nerve

tenth cranial nerve; responsible for the autonomic control of organs in the thoracic and upper abdominal cavities

Valsalva’s maneuver

voluntary contraction of the diaphragm and abdominal wall muscles and closing of the glottis, which increases intra-abdominal pressure and facilitates defecation

varicosity

structure of some autonomic connections that is not a typical synaptic end bulb, but a string of swellings along the length of a fiber that makes a network of connections with the target effector

vasa recta

branches of the efferent arterioles that parallel the course of the loops of Henle and are continuous with the peritubular capillaries; with the glomerulus, form a portal system

vascular tunic

middle layer of the eye primarily composed of connective tissue with a rich blood supply

ventral (anterior) nerve root

axons emerging from the anterior or lateral horns of the spinal cord

ventricle

central cavity within the brain where CSF is produced and circulates

ventricles

remnants of the hollow center of the neural tube that are spaces for cerebrospinal fluid to circulate through the brain

vernix caseosa

waxy, cheese-like substance that protects the delicate fetal skin until birth

vertebral arteries

arteries that ascend along either side of the vertebral column through the transverse foramina of the cervical vertebrae and enter the cranium through the foramen magnum

vestibular ganglion

location of neuronal cell bodies that transmit equilibrium information along the eighth cranial nerve

vestibule

in the ear, the portion of the inner ear responsible for the sense of equilibrium

vestibulocochlear nerve

eighth cranial nerve; responsible for the sensations of hearing and balance

villus

projection of the mucosa of the small intestine

visceral sense

sense associated with the internal organs

vision

special sense of sight based on transduction of light stimuli

visual acuity

property of vision related to the sharpness of focus, which varies in relation to retinal position

vitamins

organic compounds required by the body to perform biochemical reactions like metabolism and bone, cell, and tissue growth

vitreous humor

viscous fluid that fills the posterior chamber of the eye

voltage-gated channel

ion channel that opens because of a change in the charge distributed across the membrane where it is located

voluntary phase

initial phase of deglutition, in which the bolus moves from the mouth to the oropharynx

vulva

external female genitalia

white matter

regions of the nervous system containing mostly myelinated axons, making the tissue appear white because of the high lipid content of myelin

white rami communicantes

(singular = ramus communicans) myelinated structures that provide a short connection from a sympathetic chain ganglion to the spinal nerve that contains the preganglionic sympathetic fiber

X-linked

pattern of inheritance in which an allele is carried on the X chromosome of the 23rd pair

X-linked dominant

pattern of dominant inheritance that corresponds to a gene on the X chromosome of the 23rd pair

X-linked recessive

pattern of recessive inheritance that corresponds to a gene on the X chromosome of the 23rd pair

yolk sac

membrane associated with primitive circulation to the developing embryo; source of the first blood cells and germ cells and contributes to the umbilical cord structure

zona fasciculata

intermediate region of the adrenal cortex that produce hormones called glucocorticoids

zona glomerulosa

most superficial region of the adrenal cortex, which produces the hormones collectively referred to as mineralocorticoids

zona pellucida

thick, gel-like glycoprotein membrane that coats the oocyte and must be penetrated by sperm before fertilization can occur

zona reticularis

deepest region of the adrenal cortex, which produces the steroid sex hormones called androgens

zonule fibers

fibrous connections between the ciliary body and the lens

zygote

fertilized egg; a diploid cell resulting from the fertilization of haploid gametes from the male and female lines

α-dextrin

breakdown product of starch

α-dextrinase

brush border enzyme that acts on α-dextrins