(i) Glomerulus: The first step of urine formation, ultrafiltration, occurs from the glomerular capillaries into the lumen of the Bowman’s capsule.
(ii) Proximal convoluted tubule (PCT): In this segment, nearly 70 – 80% of water and electrolytes are reabsorbed. PCT helps in maintaining the pH and ionic balance of the body fluids, by selective secretion of H+ , ammonia and K+ into the filtrate and by absorbing bicarbonate ions.
(iii) Henle’s loop: This segment plays an important role in maintaining high osmolarity of the medullary interstitial fluid. The descending limb is permeable to water and impermeable to solutes. So filtrate becomes hypertonic. The ascending limb is, impermeable to water but permeable to solutes, so filtrate becomes hypotonic.
(iv) Distal Convoluted tubule (DCT): Reabsorption of Na+ and water takes place in this segment. DCT also reabsorbs HCO3 ions and secretes NH3+, hydrogen and potassium ions into the filtrate.
(v) Collecting duct: Large amounts of water is reabsorbed from this region. This segment also allows the transport of small amounts of urea, into the filtrate.
(v) Collecting duct: Large amounts of water is reabsorbed from this region. This segment also allows the transport of small amounts of urea, into the medullary interstitium. It also plays a role in maintaining the pH and ionic balance of the body fluids.
