Question

The accompanying figure shows reabsorption of some constituents of glomerular filtrate in different parts of the mammalian nephron. What can these constituents be?

• A. $A-N{a}^{+},B-Water,C-Urea$
• B. $A-Urea,B-N{a}^{+},C-Water$
• C. $A-Water,B-N{a}^{+},C-Urea$
• D. $A-N{a}^{+},B-Urea,C-Water$

Answer 1

The correct option is A $A-N{a}^{+},B-Water,C-Urea$

Graph A is for $N{a}^{+}$, as the $N{a}^{+}$ passes through proximal tubule, it's absorption increases. About $60$ of $N{a}^{+}$ from glomerular filtrate is absorbed here. The loop of Henle is divided into two parts

(i) Descending limb

(ii) Ascending limb.

Descending limb is impermeable but ascending limb is permeable for $N{a}^{+}$. $N{a}^{+}$ reabsorption again increases in distal convoluted tubule under the influence of aldosterone. Its absorption also occurs in collecting duct but it stabilises here.

Graph B is for water. Much of the water is absorbed in the proximal tubule. Descending limb of the loop of Henle is permeable but ascending limb of the loop of Henle is impermeable to water. As the water passes through distal tubule and collecting duct its absorption increases.

Graph C is for urea. Much of the area is absorbed in proximal tubule. Descending limb is impermeable but ascending limb is partially permeable to urea. as it passes through the distal and collecting tubule its absorption also increases.

So the correct option is A.