Inner workings of the nephron
Hyderabad: This article is in continuation to the previous articles that focused the excretory system of living beings. Proximal Convoluted Tubule (PCT): • PCT is lined by simple cuboidal brush border epithelium which increases the surface area for reabsorption. • Nearly all of the essential nutrients, and 70-80 per cent of electrolytes and water are […]
Hyderabad: This article is in continuation to the previous articles that focused the excretory system of living beings.
Proximal Convoluted Tubule (PCT):
• PCT is lined by simple cuboidal brush border epithelium which increases the surface area for reabsorption.
• Nearly all of the essential nutrients, and 70-80 per cent of electrolytes and water are reabsorbed by this segment.
• PCT also helps to maintain the pH and ionic balance of the body fluids by selective secretion of hydrogen ions and ammonia into the filtrate and by absorption of HCO3 – from it.
Henle’s Loop:
• Reabsorption is minimum in its ascending limb.
• However, this region plays a significant role in the maintenance of high osmolarity of medullary interstitial fluid.
• The descending limb of loop of Henle is permeable to water, but almost impermeable to electrolytes. This concentrates the filtrate as it moves down.
• The ascending limb is impermeable to water but allows transport of electrolytes actively or passively.
• Therefore, as the concentrated filtrate pass upward, it gets diluted due to the passage of electrolytes to the medullary fluid.
Distal Convoluted Tubule (DCT):
• Conditional reabsorption of Na and water takes place in this segment.
• DCT is also capable of reabsorption of HCO3 – and selective secretion of hydrogen and potassium ions and NH3 to maintain the pH and sodium-potassium balance in blood.
Collecting Duct:
• This long duct extends from the cortex of the kidney to the inner parts of the medulla.
• Large amounts of water could be reabsorbed from this region to produce a concentrated urine.
• This segment allows passage of small amounts of urea into the medullary interstitium to keep up the osmolarity.
• It also plays a role in the maintenance of pH and ionic balance of blood by the selective secretion of H and K ions.