Question

Name the hormone that has each of these effects on the kidneys: (p. 425) a. Promotes reabsorption of \(\mathrm{Na}^{+}\)ions b. Promotes direct reabsorption of water c. Promotes reabsorption of \(\mathrm{Ca}^{+2}\) ions d. Promotes excretion of \(\mathrm{K}^{+}\)ions e. Decreases reabsorption of \(\mathrm{Na}^{+}\)ions

Short answer

Question: Identify the hormone responsible for each of the following effects on the kidneys. a. Promotes reabsorption of Na+ ions b. Promotes direct reabsorption of water c. Promotes reabsorption of Ca+2 ions d. Promotes excretion of K+ ions e. Decreases reabsorption of Na+ ions Answer: a. Aldosterone b. Antidiuretic hormone (ADH) c. Parathyroid hormone (PTH) d. Aldosterone e. Atrial natriuretic peptide (ANP)

Step-by-step solution

a. Promotes reabsorption of Na+ ions

The hormone responsible for promoting the reabsorption of Na+ ions in the kidneys is aldosterone. Aldosterone helps regulate sodium and potassium levels in the body, and when it acts on the kidneys, it increases the reabsorption of Na+ ions back into the bloodstream.

b. Promotes direct reabsorption of water

The hormone responsible for promoting the direct reabsorption of water in the kidneys is the antidiuretic hormone (ADH). ADH acts on the collecting ducts in the kidneys, making them more permeable to water so that more water can be reabsorbed back into the bloodstream.

c. Promotes reabsorption of Ca+2 ions

The hormone responsible for promoting the reabsorption of Ca+2 ions in the kidneys is parathyroid hormone (PTH). When the blood calcium level is low, the parathyroid glands release PTH, which stimulates the kidneys to reabsorb more Ca+2 ions.

d. Promotes excretion of K+ ions

The hormone responsible for promoting the excretion of K+ ions in the kidneys is also aldosterone. Just as it aids in the reabsorption of Na+ ions, aldosterone promotes the excretion of K+ ions from the kidneys, helping to maintain the proper balance of these electrolytes in the body.

e. Decreases reabsorption of Na+ ions

The hormone responsible for decreasing the reabsorption of Na+ ions in the kidneys is atrial natriuretic peptide (ANP). ANP is released by the atria of the heart when blood pressure is high and acts on the kidneys to decrease the reabsorption of Na+ ions, which in turn, leads to an increase in urine production and a decrease in blood volume and blood pressure.

Key concepts

Aldosterone

Aldosterone plays a crucial role in regulating the balance of electrolytes in the body, specifically sodium (Na+) and potassium (K+). When aldosterone levels are high, the kidneys are signaled to reabsorb more Na+ ions from the urine back into the bloodstream, indirectly causing water to follow due to osmosis, which increases blood volume and blood pressure. Conversely, aldosterone also triggers the excretion of K+ ions into the urine to maintain electrolyte balance.

Think of aldosterone as a manager who ensures that the body holds onto the right amount of sodium while letting go of excess potassium. This delicate balance is essential for functions such as nerve signal transmission and muscle contraction, highlighting the hormone's importance in overall health and homeostasis.

Antidiuretic Hormone (ADH)

Antidiuretic Hormone, commonly known as ADH or vasopressin, functions like a water conservationist in our body. It directly influences the amount of water that is reabsorbed into the bloodstream from the kidneys. When the body needs to conserve water, ADH levels increase, making the collecting ducts of the kidneys more permeable. This allows more water to be reabsorbed, which can concentrate the urine and maintain hydration levels.

For those who often wonder why they urinate less when dehydrated, ADH is the hormone at work, minimizing water loss and protecting the body from dehydration. Its role is pivotal in managing our body's fluid balance, ensuring we retain water when necessary.

Parathyroid Hormone (PTH)

The parathyroid hormone, or PTH, serves as a key regulator of calcium levels in the blood. When calcium levels drop, the parathyroid glands secrete PTH to correct the imbalance. In the kidneys, PTH's primary job is to increase the reabsorption of calcium ions (Ca+2) from the urine back into the bloodstream.

PTH also reduces the reabsorption of phosphate, preventing too much calcium from binding to phosphate, which could lead to unwanted precipitation in the blood. Beyond its role in the kidneys, PTH stimulates the release of calcium from bones and enhances the production of active Vitamin D, further helping in raising blood calcium levels. Essentially, managing calcium with PTH is like adjusting a thermostat, ensuring the temperature - or in this case, calcium levels - stay just right.

Atrial Natriuretic Peptide (ANP)

When the heart's atria stretch due to increased blood volume and pressure, they release the hormone called Atrial Natriuretic Peptide (ANP). ANP serves as a pressure relief valve by signaling the kidneys to excrete more Na+ ions into the urine, which attracts water and results in increased urine production. Subsequently, this process lowers blood volume and pressure.

By promoting the removal of sodium and water, ANP effectively reduces the work that the heart must do, and it also helps to prevent the body from overload with excessive fluid. ANP also inhibits the release of aldosterone and ADH, creating a multifaceted approach to decrease blood pressure.