Chapter 2 Cellular Damage and Tissue Healing – Portiaa

Zoë Soon

Chapter 2 The Inflammatory Response, Fever, Healing, Cell Proliferation, Tissue Regeneration and Repair

Chapter 2 Cellular Damage and Tissue Healing – Portiaa

Zoë Soon

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Chapter 2 Learning Outcomes:

By the end of this section you will be able to:

Describe Normal Defenses of the Body:

Innate (non-specific) Defenses:
- Mechanical/Physical – skin, hair, mucus, sebum, urination, cilia, cell shedding
- Biochemical – sweat, tears & saliva (lysozymes), bile, stomach pH, cerumen, mucus, vaginal secretions, prostatic and testicular secretions,
- Normal Flora

Normal flora are microorganisms (bacteria, fungi, protozoa, and viruses) that naturally inhabit the human body. These microorganisms have a range of roles throughout the body. For example, gut microbiota (which consists of a complex and highly diverse community) help absorb nutrients and fight off infection.

- Phagocytes: (WBCs such as monocytes, fixed and free macrophages, microglia, neutrophils, eosinophils, dendritic cells) capable of diapedesis/emigration/transmigration.

Phagocytosis — A step-by-step representation of phagocytosis, a form of endocytosis where large particles are engulfed by a cell, creating an internal compartment called a “phagosome”. This cellular process is often employed by immune cells to kill invading microorganisms or remove dead cells.

Example of phagocyte: monocyte — Monocytes are the largest type of phagocytic white blood cell and play a role in adaptive immune responses and tissue repair functions. They help fight against certain infections, aid in the removal of dead or damaged tissues, destroy cancer cells, and regulate immunity against foreign substances.

Example of a phagocyte: macrophage — As an essential member of the innate immune system, macrophages (a type of white blood cell) phagocytize pathogens (microbes), cancer cells, cellular debris, and foreign substances.

Example of phagocytosis by macrophage and presentation of antigen — Macrophages can take up pathogens via endocytosis (phagocytosis). Antigens derived from the digested pathogen are then displayed on the surface of the macrophage to activate helper T cells and thus acquired immunity.

Example of a phagocyte: microglia — Microglia are immune cells of the brain. In response to neuronal cell damage, microglia remove dead and dying neurons, synapses, and dystrophic neurites.

Example of phagocytes: neutrophils — Neutrophil granulocyte migrates from the blood vessel to the matrix, secreting proteolytic enzymes, in order to dissolve intercellular connections (for improvement of its mobility) and envelop bacteria through phagocytosis.

Example of a phagocyte: neutrophil — Neutrophils, a type of white blood cell, are an essential part of the innate immune system by performing phagocytosis to remove pathogens and cell debris.

Example of a phagocyte: eosinophil — Eosinophils are a type of phagocytic white blood cell that supports the immune system in fighting against multicellular parasites and certain infections, as well as participating in allergic reactions and inflammatory responses.

Example of a phagocyte: dendritic cell — Dendritic cells (DCs) play an essential role in the defence against invading pathogens by initiating and regulating adaptive immune responses. DCs are phagocytic and degrade invading microbes.

Complement System (Classical Pathway with antibody, Lectin Pathway, and Alternative Pathway) – involving 30+ complement plasma protein cascade of activation – resulting in opsonization, MAC (Membrane Attack Complexes), stimulation of mast cells & basophils

Roles of complement cascade in innate immunity — The complement system is an essential part of immunity that promotes inflammation and enhances removal of invasive microbes and/or dead/damaged cells by antibodies or phagocytic cells.

Example of the complement system — The complement system, a part of the innate immune system, consists of approximately 40 proteins that work together to defend the host from pathogens. There are three pathways involved in complement activation: the classical pathway, the lectin pathway, and the alternative pathway.

Depiction of a MAC — The membrane attack complex (MAC) is a complex of complement proteins that form a pore in the cell membranes of invading pathogens, resulting in membrane disruption, cell lysis, and ultimately cell death. The three pathways of the complement system (classical, lectin, and alternative) all initiate the formation of MACs.

Describing role of mast cells — As members of the immune system, mast cells carry many granules of histamine, heparin, cytokines, and growth factors, and as such help fight against infection and play a integral role in allergic reactions.

Activation and role of mast cells — Mast cells are involved in allergic reactions. Following primary exposure to an allergen, large amounts of the antibody IgE are produced and attach themselves to mast cells. After a second exposure to the same allergen, the primed mast cells release many granules of histamine and other inflammatory mediators, resulting in characteristic allergy symptoms.

Description of basophil — Basophils, a type of granulocytes, help boost the immune system during pathogen infection and allergic reactions.

Cytokine family: Glycoproteins produced by WBCs, fibroblasts, endothelial cells, stromal (connect tissue) cells

Cytokines are a group of small proteins that are integral for cell signaling. (credit: adapted work from NIAID)

- Interferons: (chemical messages that stimulate defense)

Interferons are cytokines (proteins) that are released by a cell infected with a virus. The response of neighbouring cells, including cells of the immune system, helps stem the infection.

- - Alpha Interferons – produced by virally infected host cells to attract & stimulate NK cells and stimulate AVP production in neighbouring cells.
  - Beta Interferons – produced by fibroblasts to slow inflammation, and promote healing
  - Gamma Interferons – produced by T & NK cells to stimulate macrophage activity

- Chemokines: induce chemotaxis

Example of chemokines — Chemokines are a family of signaling proteins secreted by cells to induce directional movement of leukocytes (white blood cells), with movement occurring towards higher concentrations.

- Lymphokines: produced by T lymphocytes to: 1) attract macrophages & 2) stimulate B lymphocytes to produce antibodies
- Interleukins: produced by helper T cells to:
  
  1. activate macrophages and stimulate fever (act as endogenous pyrogens)
  
  2. stimulate T & B cell differentiation
  
  3. Stimulate hemopoietic cells to proliferate → producing more WBCs
- Natural Killer cells (NK Lymphocytes) – type of WBC (White Blood Cell/Leukocyte)

Natural killer (NK) cells are cytotoxic lymphocytes that play critical roles in innate immunity. (credit: adapted work from NIAID)

Inflammatory Response

Inflammatory response — In response to tissue damage or infection, the body initiates a complex inflammatory response cascade with the goal of healing the affected area.

Fever – speeds up WBC activity and repairs, inhibits pathogen activity

Describe plasma components & define vocabulary words:

Hematopoietic cells: location and derivation — The development of blood cells, including white blood cells, red blood cells, and platelets, during hematopoiesis. The body produces approximately 100 billion blood cells every day.

- Plasma – liquid matrix containing water, electrolytes, and plasma proteins

A bag containing one unit of fresh frozen plasma, a liquid matrix containing water, electrolytes, and plasma proteins.

- Plasma proteins – antibodies, complement proteins, clotting factors, albumen and transporter proteins

Antibodies are proteins (immunoglobulins) essential to the functioning of the immune system as they recognize foreign particles for neutralization. (credit: adapted work from NIAID)

Structure of antibody molecule (protein). These molecules circulate in the blood, recognize foreign particles, and neutralize them.
- Platelets/Thrombocytes – a nuclear cell fragments formed from large megakaryocytes; involved in clotting (hemostasis)

Platelets in a Giemsa-stained blood film. — Platelets (purple) in a Giemsa-stained blood film. Platelets are small, colourless cell fragments in the blood that aid in clotting.

- Leukocytes – WBCs
- Lymphocytes: type of WBC involved in antibody production (B lymphocytes), targeted immune response (T lymphocytes), and surveillance (NK lymphocytes)
- Neutrophils: The most abundant phagocyte in the blood; contain extensive lysosomes
- Eosinophils: Destroy parasitic worms & immune complexes
- Basophils & Mast cells: Release histamine, heparin, prostaglandins, and leukotrienes in process known as degranulation

Leukocytes — Types of leukocytes (white blood cells) that help the body fight infection and other diseases.

The characteristics and location of cells involved in the innate immune system are described. (credit: modification of work by NIH)

- Erythrocytes – RBCs; transport oxygen & carbon dioxide

Erythrocytes — Blood smear with Wright’s stain visualizing erythrocytes (pink). Red blood cells (RBCs) are the most common type of blood cell, circulating in the blood and delivering oxygen to tissues around the body.

- Hematocrit – % by volume of blood that is formed elements
- Anemia: reduced oxygen-carrying capacity of blood due to low levels of functional RBCs or hemoglobin.

iron-deficiency anemia — Iron-deficiency anemia is the most common form of anemia, a blood disorder that affects the function of red blood cells (RBCs). Iron deficiency inhibits the production of sufficient hemoglobin, reducing RBC’s ability to transport oxygen around the body.

- - Polycythemia; greater than normal # of RBCs
  - EPO, erythropoietin: hormone that stimulates production of RBCs

Describe 3 stages of hemostasis: vascular spasm (role of endothelin and tunica media), platelet plug formation (extrinsic and intrinsic pathways, roles of Factor X, thrombin, clotting factors, and Ca++) and coagulation (role of fibrin)

Basic diagram of the series of events that occur after a wound, starting with the attraction of platelets to the wound site, the cascade reactions, activation of clotting factors, and ending with the conversion of fibrinogen into fibrin and scab formation. (Note: Not all 13 clotting factors are explicitly pointed out; blue clotting factors are inactive, green are active, and black is the activated fibrinogen).

Extrinsic and Intrinsic pathways of blood coagulation — The components and pathways that make up the classical blood coagulation cascade.

Describe stages of healing: fibrinolysis (role of tPA, and plasmin) and regeneration (role of PDGF)

Describe components of the Lymphatic System:
- Lymph Vessels
- Lymph Nodes

Lymphatic vessels carry a clear fluid called lymph throughout the body. Lymph nodes are filled with lymphocytes that purge infecting cells. — Lymphatic vessels carry a clear fluid called lymph (contains white blood cells) throughout the body. Lymph nodes are filled with lymphocytes that purge infecting cells.

- Lymphocytes (Helper T, Cytotoxic T, Memory T, Suppressor/Regulator T, B, Memory B, plasma cells), Cell-mediated and Humoral Immunity

B cell activation — T and B Cell Binding To elicit a response to a T cell-dependent antigen, the B and T cells must come close together. To become fully activated, the B cell must receive two signals from the native antigen and the T cell’s cytokines.

- Macrophages, Dendritic Cells
- Primary and Secondary Response, Vaccination

In the primary response to infection, antibodies are secreted first from plasma cells. Upon reexposure to the same pathogen, memory cells differentiate into antibody-secreting plasma cells that output a greater amount of antibody for a longer period of time. — In the primary response to infection, antibodies are secreted first from plasma cells. Upon re-exposure to the same pathogen, memory cells differentiate into antibody-secreting plasma cells that output a greater amount of antibody for a longer period of time.

Primary and secondary immune response — Clonal Selection of B Cells During a primary B cell immune response, both antibody-secreting plasma cells and memory B cells are produced. These memory cells lead to the differentiation of more plasma cells and memory B cells during secondary responses.

Vaccines are often delivered by injection into the arm. (credit: Navy Medicine) — Vaccines are often delivered by injection into the arm (credit: Navy Medicine).

- Antibody Roles – Neutralization, Agglutination, Precipitation, Opsonization

Antibody actions: opsonization, agglutination, neutralization, and activation of complement — Antibody receptor binding to ligand through process of **A: opsonization** (tagging for phagocytosis); **B: agglutination** (antigens clumping with antibodies); **C: neutralization** (preventing foreign pathogens from replicating, entering healthy cells, and causing infection); and **D: activation of the complement** cascade (enhances antibody activity to attack the cell membranes of pathogens, clear pathogens and damaged cells, and promote inflammation). The complement membrane attack complex (MAC) is a transmembrane channel that causes osmolytic lysis of the target cell.

- Cytotoxic T cell activity – perforin, lymphotoxin, apoptosis

cytotoxic t cell activity — One of the most important roles of the immune system is to clear the body of viruses and cancer cells. This job is performed by cytotoxic T cells which hunt down and destroy tumors and virally-infected cells. In this immunofluorescence image, a cytotoxic T cell (CTLs; blue) is engaging a target cell. A patch of signaling molecules (pink) that gathers at the site of cell-cell contact indicates that the CTL has identified a target. Lytic granules (red) that contain cytotoxic components then travel along the microtubule cytoskeleton (green) to the contact site and are secreted, thus killing the target.

- Explain cause of Inflammation – innate (non-specific) response to tissue injury; caused by: tissue damage from cuts, sprains, chemicals, ischemia, heat, cold, infections, or foreign objects

Example of cause of inflammation: microglia — **Microglial cells surrounding area of inflammation after ischemic stroke.** In response to inflammatory signals, microglia, along with other inflammatory cells, are activated and aggregate at the lesion site.

- - Stimulated by vasoactive chemicals released by mast cells: histamine, prostaglandin, leukotrienes – all induce: vasodilation, increased capillary permeability, bronchoconstriction, mucous production (stim. gland secretion), and chemotaxis of WBCs

In response to a cut, mast cells secrete histamines that cause nearby capillaries to dilate. Neutrophils and monocytes leave the capillaries. Monocytes mature into macrophages. Neutrophils, dendritic cells, and macrophages release chemicals to stimulate the inflammatory response. Neutrophils and macrophages also consume invading bacteria by phagocytosis.

- Explain 5 signs of Inflammation:
  - Redness & warmth: due to ↑ blood flow (hyperemia) to damaged area
  - Swelling (edema): protein & fluid into interstitial space
  - Pain: increased pressure of fluid on nerves; release of chemical mediators – i.e., bradykinins, histamine (itch), prostaglandins
  - Loss of function: may develop if cells lack nutrients; edema may interfere with movement

Inflammation of the bursa of the elbow, characterized by redness, swelling and pain at the tip of the elbow. Loss of function can also occur.

Explain 2 phases of inflammation:

1. Vascular: vasodilation & increased cap perm → exudate (fluid); stagnation of flow & clotting of blood occurs which aids in localizing the spread of infectious microorganisms.
- - Histamine, Leukotrienes, Bradykinin, Prostaglandins: induces vasodilation, increased capillary permeability
  - Histamine: additionally induces itch
  - Prostaglandins: additionally induce pain, fever
  - Bradykinogen (plasma protein): additionally induce pain when in active bradykinin form
  - Histamine receptors found on nerve endings and on blood vessel walls
2. Cellular: – emigration (diapedesis) of WBCs; Production of more WBCS (e.g. neutrophils, shift to the left)

Four types of Exudate:
1. Serous: watery, consists primarily of fluid, some proteins, & WBCs (e.g. allergic rxns & burns);

2. Fibrinous: thick, sticky, high cell & fibrin content; Increased risk of scar tissue (e.g. severe injuries, rheumatic heart disease, bacterial pneumonia)

3. Purulent (“pus”): thick, yellow-green, contains more WBCs, cell debris, & microorganisms; Bacterial infection *An abscess contains purulent exudate

A swollen, pus-filled eye with conjunctivitis. Purulent discharge, thick, milky or yellowing pus (exudate), is a mixture of dead cells, bacteria, and white blood cells.

4. Hemorrhagic: blood from damaged blood vessels

Mild fever (pyrexia) – oral temp above 38ºC; (Side note: Heatstroke = 40ºC or higher)
- Common if inflammation is extensive (can occur with heart attack, stroke, trauma, cancer)
- Due to WBC release of endogenous pyrogens (interferons, interleukins) or (LPS= LipoPolySaccharide = slimy coat of bacteria = exogenous pyrogen)
  
  ¤What is the most accurate way to take someone’s temperature? Rectal
  
  ¤What is preferred method? Tympanic for elderly and Axillary for babies
  
  ¤What is FUO? Fever of Unknown Origin (unknown drug rxn; undetectable infection/trauma/injury/cancer/heart attack/blood clots/inflammatory disease)
  
  ¤What is a blunted/absent febrile response to infection? Indicates poorer immune response
What is Systemic Inflammatory Response Syndrome? Can be in response to burn or infection and is as follows: Enormous release of inflammatory cytokines → systemic vasodil. & cap perm → low BP → Circulatory/Septic shock (can be fatal)
- Malaise (Feeling unwell), Fatigue, Headache, Anorexia
- Decreased mental function (in elderly) due to cerebral hypoxia

- Describe the 4 stages of Fever
  - Prodromal
  - Chills
  - Flush
  - Defervescence (Sweating)
- Define and explain the significance of:
  - Leukocytosis
  - Differential Count

A differential count measures the percentages of each type of leukocyte present in a blood sample.

- - Plasma
  - Erythrocyte Sedimentation Rate

The erythrocyte sedimentation rate (ESR) is the rate at which red blood cells in anticoagulated whole blood descend in a standardized tube over a period of one hour.

- - C-reactive protein
  - Neutrophilia
  - Neutropenia
  - Lymphocytosis
  - Lymphocytopenia
  - Thrombocytopenia

Peripheral blood smear indicating thrombocytopenia (low platelet count). Red arrow pointing at platelet.

- - Eosinophilia
  - Scar Tissue

Tissue healing — Tissue Healing: During wound repair, collagen fibers are laid down randomly by fibroblasts that move into repair the area.

- - Cellular Regeneration
  - Cellular Resolution
  - Cellular Replacement
  - Granuloma; Granulation tissue
  - Healing by 1st Intention
  - Healing by 2nd Intention
  - Angiogenesis
- Explain the presence of liver/heart proteins in blood
- Explain possible complications of inflammation
  - Infection
  - Deep ulcers
  - Skeletal Muscle Spasms
  - Chronic inflammation