Question

The avascular organ of the brain monitors blood osmolarity and signals the release of ADH in a negative feedback system. When you eat salty foods, the osmolarity of your blood rises above the set point. Can you predict what will happen next?

Or

How does the human body maintain a constant blood osmolarity?

A. Because ADH is not released into the bloodstream, a large amount of urine is produced.

B. ADH is released into the bloodstream, and water is reabsorbed.

C. ADH is not released into the bloodstream, and water is reabsorbed.

D. ADH would not be released, resulting in a large amount of urine being produced.

Answer 1

Recall the concept of a negative feedback system. In a negative feedback system, the response to a stimulus is opposite to the stimulus itself. In this case, the stimulus is an increase in blood osmolarity. The response is the release of ADH, which helps to decrease blood osmolarity.

Complete step-by-step Answer: When you eat salty food, your blood osmolarity rises above the set point. This triggers the release of ADH from the hypothalamus into the bloodstream. ADH acts on the kidneys to increase water reabsorption, which helps to lower blood osmolarity back to normal levels.

Here's a more detailed explanation of the process:

1. Salt intake increases blood osmolarity. When you eat salty food, the salt is absorbed into your bloodstream, which increases the concentration of dissolved particles in your blood. This increase in concentration is called blood osmolarity.

2. Osmoreceptors detect the increase in blood osmolarity. Osmoreceptors are specialized cells located in the hypothalamus that are sensitive to changes in blood osmolarity. When blood osmolarity rises, osmoreceptors send signals to the hypothalamus.

3. The hypothalamus releases ADH. The hypothalamus is a part of the brain that plays a role in regulating many important body functions, including fluid balance. When it receives signals from osmoreceptors, the hypothalamus releases ADH, also known as vasopressin.

4. ADH increases water reabsorption by the kidneys. ADH travels through the bloodstream to the kidneys, where it binds to receptors on the collecting ducts of the nephrons. These receptors trigger the insertion of aquaporin-2 water channels into the cell membrane of the collecting duct cells. Aquaporin-2 channels allow water to move freely across the cell membrane, increasing water reabsorption from the urine back into the bloodstream.

5. Blood osmolarity decreases. As water is reabsorbed from the urine, the concentration of dissolved particles in the blood decreases, and blood osmolarity returns to normal levels.

Therefore, when you eat salty food and your blood osmolarity rises, ADH is released into the bloodstream to increase water reabsorption by the kidneys, which helps to lower blood osmolarity back to normal. This is an example of a negative feedback system, as the release of ADH counteracts the increase in blood osmolarity.

Hence the correct answer is Option B

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Additional Information: The hypothalamus is not the only organ that monitors blood osmolarity. The kidneys themselves also have osmoreceptors that can detect changes in blood osmolarity and release ADH accordingly.

Note: This is an example of a negative feedback system because the response of ADH secretion (a decrease in urine output) counteracts the initial stimulus (an increase in blood osmolarity). This helps to maintain a stable blood osmolarity, which is important for normal body function.