Question Video: Describing the Role of ADH in the Regulation of Water Balance in the Human Body Biology

Which of the following statements best describes how ADH helps regulate water balance? [A] If present, ADH increases the permeability of the collecting duct, so more water is excreted in urine. [B] If present, ADH decreases the permeability of the collecting duct, so more water is excreted in urine. [C] If present, ADH increases the permeability of the collecting duct, so more water is reabsorbed into the bloodstream. [D] If present, ADH increases the permeability of the collecting duct, so there are higher concentrations of glucose reabsorbed into the blood. [E] ADH has no effect on the regulation of water balance in the body.

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Video Transcript

Which of the following statements best describes how ADH helps regulate water balance? (A) If present, ADH increases the permeability of the collecting duct, so more water is excreted in urine. (B) If present, ADH decreases the permeability of the collecting duct, so more water is excreted in urine. (C) If present, ADH increases the permeability of the collecting duct, so more water is reabsorbed into the bloodstream. (D) If present, ADH increases the permeability of the collecting duct, so there are higher concentrations of glucose reabsorbed into the blood. Or (E) ADH has no effect on the regulation of water balance in the body.

ADH is an acronym that stands for antidiuretic hormone. A diuretic is a substance that increases urine production, and anti- is a prefix that means not or the opposite of. So, ADH is a hormone that decreases urine production in the body. ADH is produced in the brain, and it’s carried by the bloodstream to the kidneys, which are the organs in our body responsible for producing urine. And the production of urine is one of the main ways that our body regulates the amount of water contained in the bloodstream, also referred to as water balance.

That being said, we can draw some conclusions about the relationships between ADH, urine, and water excretion. An increase in ADH would lead to a decrease in urine production. And since less urine is being made, less water is being removed from the body. In contrast, a decrease in ADH production would lead to an increase in urine, which would mean that more water is being excreted from the body.

Well, the kidney makes urine in millions of tiny structures called nephrons. And what I’ve drawn is an extremely simplified diagram that we can use as an illustration. So, how the nephron works is that blood enters from the renal artery and then flows through a special structure called a glomerulus.

In the glomerulus, all of the small molecules filter out of the bloodstream, and this includes most of the water. This liquid, now called filtrate, enters the renal capsule, also called a Bowman’s capsule. The filtrate flows from the capsule into a long, twisted tubule. And from the tubule, everything that is not considered waste is passed back into the bloodstream, which includes most of the water. What’s left in the tubule is now considered urine. Several nephrons empty into one collecting duct, which join into larger and larger vessels until they exit the kidney through the ureter.

So how does ADH change how much urine is produced? Well, ADH affects urine production by changing the permeability of the collecting ducts and the tubules. And permeability means the ability of water to pass through the linings of these vessels. When more water is able to pass from the collecting duct and back into the bloodstream, there’s less water present in the urine. So, the volume of the urine decreases.

So, we can summarize what we’ve learned in that if ADH is present in the bloodstream, less urine is produced. That’s because ADH increases the permeability of the ducts and tubules in the nephrons, which allows more water to be reabsorbed into the bloodstream. Since more water is reabsorbed, less water is excreted and we have a lower volume of urine.

Now, we know everything we need to know to choose the correct answer to our question. So, now, we can review our answer choices again and choose the correct one. I’d like to start with choice (D), which refers to the concentration of glucose. This choice doesn’t answer the question of how water balance is regulated. And then choice (E) says that ADH has no effect on the regulation of water balance in the body. But we know that ADH affects urine production, which indeed affects water balance.

So that leaves us with the choices (A), (B), and (C), which each describe relationships between ADH, permeability, and the amount of water either excreted or reabsorbed. If we examine them carefully, we find that the correct choice is (C), which states, if present, ADH increases the permeability of the collecting duct so that more water is reabsorbed into the bloodstream.

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