Question

Explain the following term:

Selective reabsorption.

Answer 1

Selective reabsorption:

1. The reabsorption of filtered molecules, i.e. H⁺ Na⁺, K⁺, ions from the glomerular filtrate in the tubules to the blood is called selective reabsorption.
2. About 85% of the 180L of filtrate formed per day is reabsorbed by this process.

Reabsorption in proximal convoluted tubule:

1. It reabsorbs approximately 80% H₂O, Na⁺, K⁺, HCO₃^-. ions, entire glucose and amino acids.
2. Some amount of Vitamin C is also reabsorbed.
3. It also helps in maintaining the pH and ionic balance of the body fluids by selective secretion of H⁺ ions.

Reabsorption in loop of Henle:

1. About 15% of the filtered water is removed from the descending limb of Henle because it is permeable to water.
2. Filtrate in descending limb becomes hypertonic to plasma.
3. The thick segment of the ascending limb co-transports Na⁺, K⁺ and Cl^- ions.
4. Bivalent ions like Mg²⁺, Ca²⁺ etc., are also reabsorbed actively in this region.
5. In ascending limb movement of Na⁺, Cl^- takes place out of the tubular.
6. Thus, the fluid becomes hypotonic to plasma.

Reabsorption in distal convoluted tubule:

1. Water reabsorption is facultative here which is regulated by Antidiuretic hormone (ADH).
2. Reabsorption of water in DCT in the influence of ADH depends on amount of fluid intake by the body.