One substance has no membrane transporters to move it but can diffuse freely through open leak channels if there is a concentration gradient. Initially, this substance's concentrations in the filtrate and extracellular fluid are equal. Later, however, the active transport of Na + and other solutes creates a gradient by removing water from the lumen of the tubule where it is located. What substance is this?

Question

Irene Mccoy

Biology

6 October, 00:29

One substance has no membrane transporters to move it but can diffuse freely through open leak channels if there is a concentration gradient. Initially, this substance's concentrations in the filtrate and extracellular fluid are equal. Later, however, the active transport of Na + and other solutes creates a gradient by removing water from the lumen of the tubule where it is located. What substance is this?

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Answers (1)

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Hazel Nunez · Answer 1

Urea

Explanation:

Urea is a small nitrogenous compound which is the main end product of protein catabolism in mammals

Urea is a nitrogen-containing substance normally cleared from the blood by the kidney into the urine It is made predominantly in the liver from ammonia and bicarbonate and is one of the main components of urine The rate of synthesis varies from 300 to 600 mmol/day depending on the protein intake All of this urea eventually finds its way into the urine Because urea makes up a large part of the obligatory solute excretion, its osmotic pressure requires significant volumes of water to carry the urea Urea passively crosses biological membranes, but its permeability is low because of its low solubility in the lipid bilayer Some cells speed up this process through urea transporters, which move urea by facilitated diffusion Urea is passively reabsorbed in the proximal tubule, but its route of transport is not clear Urea transporters have not yet been identified for the proximal tubule