Question

Discuss the action of nephrons in the urinary system. Describe the different parts of the nephron and what happens in them?

Answer 1

Structure of a nephron:

• Nephron is the structural and functional unit of kidney. There are many nephrons in the kidney.
• Each nephron consists of glomerulus and renal tubule.
• The glomerulus is a tuft of capillaries. The afferent arteriole brings in blood to be filtered into the glomerulus. The efferent arteriole takes the filtered blood away from the glomerulus.
• The renal tubule can be distinguished into different parts namely Bowman's capsule, proximal convoluted tubule (PCT), Henle's loop, distal convoluted tubule (DCT) and collecting duct.
• The glomerulus is enclosed within the cup shaped Bowman's capsule.
• The Bowman's capsule leads to a highly coiled portion called PCT, which in turn leads to a U-shaped portion called Henle's loop.
• The Henle's loop has a descending limb and an ascending limb.
• The ascending limb leads to a highly coiled portion called DCT.
• The DCT finally leads to an erect tube like structure called collecting duct.

Functions:

• The main function of nephron is urine formation. It involves three steps, namely- filtration, reabsorption and secretion.
• Filtration of blood occurs in the glomerulus through three layers namely, endothelium of glomerulus, epithelium of Bowman's capsule and the basement membrane. This results in fine filtration. Therefore, glomerular filtration of blood is called as 'ultrafiltration'.
• The filtrate formed is passed on to the renal tubule where it undergoes reabsorption.
• Maximum reabsorption occurs in PCT. Water,nutrients and electrolytes are reabsorbed from the filtrate.
• Very small amount of water and ions are reabsorbed in the descending and ascending limb of Henle's loop respectively.
• Very less reabsorption of water and ion occurs in DCT (conditional).
• Large amount of water is reabsorbed in the collecting duct (conditional).
• The reabsorbed contents from filtrate passing through PCT, DCT and collecting duct, are transported to the blood flowing through peritubular capillaries.
• The reabsorbed contents from filtrate passing through Henle's loop, is transported to vasa recta.
• The last step is secretion of unwanted contents into the renal tubule.
• Hydrogen ions, potassium ions, creatinine, urea ,certain drugs and ammonium ions are secreted from the blood flowing through peritubular capillaries into the filtrate in the PCT.
• Urea is secreted into the filtrate in Henle's loop.
• Hydrogen ions, potassium ions, ammonium ions and certain drugs are secreted into the filtrate in DCT.
• Hydrogen ions, ammonium ions and potassium ions are secreted into the filtrate in collecting duct.
• The end result of the whole process is concentrated urine.