The function of the kidney is:
1) to excrete waste products, such as urea, uric acid, ammonia, and phosphate
2) to maintain homeostasis of the body fluid volume and solute composition
3) help control plasma pH
Each kidney is a fist-sized organ made up of an outer cortex and an inner medulla. Urine is created by the kidney and emptied into the renal pelvis. The renal pelvis is emptied by the ureter which carries urine to the bladder. The bladder is drained by the urethra.
The functional unit of the kidney is the nephron. Blood flows into the first capillary bed of the nephron called the glomerulus. Together, Bowman's capsule and the glomerlus make up the renal corpuscle. Hydrostatic pressure forces some plasma through fenestrations of the glomerular endothelium and into Bowman's capsule.
The proximal tube is where most reabsorption takes place.
Drugs, toxins, and other solutes are secreted into the filtrate by the cells of the proximal tube. Hydrogen ions are secreted through an antiport system with sodium, which is driven by the sodium concentration gradient.
The net result of the proximal tubule is to reduce the amount of filtrate in the nephron while changing the solute composition without changing the osmolarity.
The filtrate flows into the loop of Henle. Its function is to increase the solute concentration, and thus the osmotic pressure, of the medulla. The descending loop of Hendle has low permeability to salt. The ascending loop of Hendle is nearly impermeable to water.
The distal tubule reabsorbs Na+ and Ca2+ while secreting K+, H+, and HCO3-.
ADH acts to increase the permeability of the cells to water. Therefore, in the presence of ADH, water flows from the tubule, concentrating the filtrate.
The juxtaglomerular apparatus monitors filtrate pressure in the distal tubule.
Filtration occurs in the renal corpuscle.
Secretion occrus in the proximal tubule.
The function of the kidney is homeostasis.