IMAT 2020 Q37 [Reabsorption of Water]

Which one of the structures listed is NOT involved in the reabsorption of water in a healthy human?

A. distal convoluted tubule
B. collecting duct
C. proximal convoluted tubule
D. glomerulus
E. loop of Henle

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The correct answer is D.

All of these elements belong to the nephron, which is the structural unit of the kidney.

There is no real way around it : to understand this question, we have to make a diagram :

Therefore, the following structures are involved in water retention :

  1. Proximal convoluted tube : it is very permeable to sodium (Na+). To maintain osmolarity, water is also reabsorbed. It is the same for the distal tube.

  2. Loop of Henle : it is permeable to water but not to ions on its downwards portion and vice versa on its upward portion.

  3. Collecting duct : its permeability is regulated by vasopressin. It is involved in water retention.

The glomerulus however, isn’t involved in the processes of water reabsorption. Its purpose is to filtrate the blood that reaches the nephron. For example, glucose, ions and fluids are all removed from the glomerular capillaries.

The red line represent the afferent and efferent arteries that go through the glomerulus.

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