Question

Which function of which of the following is under normal hormonal control?

a. Distal tubule

b. Ascending loop of Henle

c. Proximal tubules

d. Descending loop of Henle

Answer 1

Question.

Which function of which of the following is under normal hormonal control?

Answer: a) Distal tubule.

Explanation: The reabsorption of water and solutes in the distal convoluted tubules of the nephron is largely under the control of hormones like aldosterone, atrial natriuretic peptide and parathormone.

The aldosterone secreted by adrenal medulla causes reabsorption of sodium ions and water as well as excretion of potassium ions from the distal tubule. Atrial natriuretic peptide which is secreted by the cardiac cells in response to increased plasma volume causes secretion of sodium ions and water into the tubules causing their excretion thereby reducing the plamsa volume. Parathormone which is a peptide hormone synthesized by parathyroid gland causes reabsorption of calcium ions and excretion of phosphate ions from the distal tubule.

Ascending limb of loop of henle is impermeable to water by permeable to sodium ions. Therefore, sodium ions are actively pumped out from the tubular fluid into the interstitial fluid, increasing the concentration of interstitial fluid and making the tubular fluid hypotonic.

Proximal tubules of the nephron have tightly packed microvilli called brush border which increases their reabsorptive capacity. Glucose and amino acids which enters the proximal tubules are entirely reabsorbed. A huge amount of sodium ions, water, phosphate ions, urea and other solutes are also reabsorbed. Most of the ions and water are reabsorbed from the proximal tubules by active transport mechanism using ionic pumps like Na+-K+ ATPase.

Descending loop of henle is permeable to water and not so permeable to solutes. Hence, water moves out of the tubular fluid into the interstitial fluid mainly by the process of osmosis but the solutes remain inside the the tubule thus making the tubular fluid hypertonic.