Functions of the nephron

Kidneys are bean shaped organs which filter blood to regulate levels of waste, water and salt in body fluids. The nephron is the kidney’s functional unit. In its first section, renal corpuscle, filtration occurs as fluid and small molecules in blood are filtered from glomerular capillaries. The filtrate is captured within a chamber called Bowman’s capsule. The next nephron section, the renal tubule has three parts in series. Filtrate within Bowman’s capsule enters the proximal convoluted tubule. Reabsorption of important molecules and ions from filtrate back into blood occurs here. These include glucose, amino acids, vitamins, water, sodium, chloride, bicarbonate and potassium. Blood vessels receiving reabsorbed species are peritubular capillaries a plexus derived from the arterial leaving the renal corpuscle The renal tubule continuous as the Loop of Henle, which has a descending limb passing into the kidney medulla and an ascending limb returning to the kidney cortex. Tubular fluid in the loop undergoes significant changes in osmotic concentration. A kind of current multiplier system functions to allow water only to leave the filtrate by osmosis during loop descent and salt only to leave the filtrate by active transport during loop ascent. This creates an osmotic gradient in medulla interstitial fluid. This is necessary to produce concentrated urine. A capillary system, vasa recta, parallels the Loop of Henle and participates in salt gradient formation and maintenance. In the distal convoluted tubule secretion occurs. Some wastes, ammonia, uric acids, hydrogen ions, penicillin are secreted from blood vessels into the renal tubule. If concentrated urine must be produced because of low fluid levels antidiuretic hormone acts on collecting duct lining cells-tube section after distal convoluted tubule, promoting water movement from filtrate into interstitial space because of osmotic gradient established and maintained by fluid inside movement associated with the Loop of Henle.