In kidneys, urine is produced by three processes as____________
Urine formation in humans takes place by three processes -
Ultrafiltration: It takes place in the Malpighian corpuscle, Henle’s loop PCT and DCT. Blood is filtered so finely through the membranes of Bowman's capsule, that almost all the constituents of the plasma except the proteins pass into the lumen of the Bowman’s capsule. Therefore, it is considered a process of ultrafiltration.
Tubular reabsorption: A comparison of the volume of the filtrate formed per day (180 litres per day) with that of the urine released (1.5 litres), suggest that nearly 99 per cent of the filtrate has to be reabsorbed by the renal tubules. This process is called reabsorption.
Tubular Secretion: The tubular epithelial cells in different segments of nephron perform this either by active or passive mechanisms. During urine formation, the tubular cells secrete substances like H+, K+ and ammonia into the filtrate. Tubular secretion is also an important step in urine formation as it helps in the maintenance of ionic and acid-base balance of body fluids.