Question

Which of the following mechanisms is NOT important in the maintenance of the osmotic gradient within the proximal tubule that drives water movement?

1) cotransport of chloride
2) cotransport of amino acids
3) cotransport of glucose
4) active reabsorption of sodium
5) diffusion of urea

Answer 1

The diffusion of urea is NOT important in the maintenance of the osmotic gradient within the proximal tubule that drives water movement. Mechanisms like the cotransport of ions and organic molecules, as well as active sodium reabsorption, establish the gradient necessary for water reabsorption.

Step-by-step explanation:

Among the mechanisms listed that contribute to the maintenance of the osmotic gradient within the proximal tubule and drive water movement, the mechanism that is NOT important is the diffusion of urea. Cotransport of chloride, cotransport of amino acids, cotransport of glucose, and active reabsorption of sodium all play vital roles in creating and sustaining the osmotic gradient for water reabsorption. Through processes like secondary active transport and facilitated diffusion, these mechanisms facilitate the transfer of substances like glucose and ions across the cell membranes, which is critical for the recovery of solutes and water from the filtrate. Symport mechanisms involve the transport of Na+ alongside other substances such as glucose, which is then followed by water movement to balance the ensuing osmotic gradient. However, diffusion of urea does not significantly contribute to the osmotic gradient in the proximal tubule.