Excretory Products And Their Elimination

Glomerulus is a tuft of capillaries. Blood enters the glomerulus through afferent arteriole and leave it through efferent arteriole. The glomerular capillaries are narrower than the afferent renal arterioles. Therefore the blood pressure in the glomerular capillaries becomes very high so that there is continuous process of ultrafilteration through the semipermeable glomerular capillaries membrane. Hence, water and many dissolved substances from the blood are filtered into the lumen of theBowmans capsule through its walls. This filterate contains a large amount of water and other dissolved substances such as urea, uric acid amino acids, glucose, K, Na, vitamins etc. Water is reabsorbed in the distal convoluted tubule and collecting duct of nephron. Reabsorption of sodium takes place in proximal convoluted tubule and asscending limb of loop of Henle.

When the tubular fluid leaves the loop of Henie and flows into the distal convoluted tubule the fluid is dilute. As fluid flows into the cortical collecting tubule amount of water reabsorbed is depend on concentration of ADH. There is further water reabsorption in medullary collecting duct. The urine is hypertonic (i.e., it has a higher osmotic pressure than the blood plasma).