Kidney’s Roles include:

Filtering Blood and constantly maintaining Salt-Water Balance and pH of the Blood:

Physiology Overview:

1. Blood enters via the afferent arteriole into the glomerulus—a network of leaky capillaries.
2. Filtrate is collected in the Bowman’s capsule; normally, about 142 liters/day of filtrate is produced, but only 2 liters/day is normally excreted as urine.
3. The kidneys reabsorb most of the filtrate, removing waste while conserving water, nutrients, and electrolytes.

Detailed Steps of Nephron Function:

1. The renal artery brings oxygenated blood, dividing into arterioles to distributes blood throughout the kidney.
2. Each afferent arteriole brings blood into a glomerular capillary clustered inside a Bowman’s (renal) corpuscle.
3. The hydrostatic pressure of afferent arterioles is high (~55mmHg), and the glomerular capillaries are very leaky (sinusoid capillaries), meaning that blood filtration occurs at each glomerulus.
4. The Bowman’s capsule captures the filtrate, which consists of water and small solutes that filter out leaving blood plasma.
5. The solutes contain nitrogenous wastes (urea, uric acid and creatinine) as well as excess salts (e.g. NaCl), excess H+ (acid). This allows the kidney to perform its main role of constantly maintaining water-salt balance and pH of the blood.
6. The filtrate continues through nephron tubule and much of the water as well as small nutrients (e.g., amino acids, glucose) are reabsorbed back into the bloodstream of the surrounding peritubular capillaries.
7. The filtrate passes down the collecting duct of the nephron into the minor calyces, the major calyces, the renal pelvis and down the ureters to the bladder.  Urine contains nitrogenous wastes (urea, uric acid, creatinine), excess salt, excess acid (H+), drug & hormone breakdown products, and excess water.