Biology · Excretory Products and Their Elimination · NEET
Per NCERT: the DCT does conditional reabsorption of Na+ and water, and reabsorbs HCO3-. It also does selective secretion of H+, K+ and NH3 (ammonia) into the filtrate. So it takes back sodium, water and bicarbonate, and pushes out hydrogen, potassium and ammonia.
PCT reabsorption is bulk and automatic - it always takes back nearly all nutrients and 70-80% of water and electrolytes. DCT reabsorption is 'conditional' because it happens only when the body needs it and is controlled by hormones (aldosterone increases Na+ and water reabsorption; ADH also acts here and on the collecting duct). This is why the DCT is the fine-tuning site, not the bulk site.
The DCT can reabsorb Na+, but the classic NEET answer for the site of active Na+ reabsorption is the PCT, not the DCT. NCERT lists 'conditional reabsorption of Na+ and water' as the DCT function. So in a match/site question, active bulk Na+ reabsorption = PCT, while conditional (hormone-controlled) Na+ reabsorption = DCT.
The DCT selectively secretes H+ (hydrogen ions) and NH3 (ammonia) into the filtrate and reabsorbs HCO3- (bicarbonate) back into the blood. Removing acid (H+) and keeping the base (HCO3-) raises and stabilises blood pH. The PCT also does H+ and ammonia secretion, so both segments guard pH and ionic balance.
Yes. The DCT, along with the afferent arteriole, forms the juxta glomerular apparatus (JGA) where they touch. The DCT lies in the cortical region of the kidney (like the Malpighian corpuscle and PCT), while the loop of Henle dips into the medulla. The DCT then leads into the collecting duct.
The part of nephron involved in active reabsorption of sodium is
Match the following parts of a nephron with their function: (a) Descending limb of Henle's loop (b) Proximal convoluted tubule (c) Ascending limb of Henle's loop (d) Distal convoluted tubule; (i) Reabsorption of salts only (ii) Reabsorption of water only (iii) Conditional reabsorption of sodium ion (iv) Reabsorption of ions, water and organic nutrients
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Fine-tuning of urine: conditional reabsorption of Na+ and water, reabsorption of HCO3-, and secretion of H+, K+ and NH3 to control blood pH and ion balance.
Aldosterone increases conditional Na+ and water reabsorption at the DCT; ADH (vasopressin) also promotes water reabsorption in the DCT and collecting duct.
The DCT helps adjust water and ions but the strong concentration of urine happens in the collecting duct using the medullary osmotic gradient. The DCT is mainly for fine adjustment.
In the cortical region, along with the Malpighian corpuscle and PCT. The loop of Henle dips into the medulla, and the DCT opens into the collecting duct.
The DCT does conditional Na+/water reabsorption and pH secretion (H+, K+, NH3). The collecting duct does the final large water reabsorption (under ADH) to make concentrated urine and can secrete H+/K+ too.
