Question

Antidiuretic hormone a. causes vasodilation of blood vessels. b. stimulates aldosterone production by the adrenal glands. c. stimulates reabsorption of both Na+ and water from the kidneys. d. is stimulated by AII. e. increases water but not ion reabsorption in the kidneys.

Short answer

The hormone antidiuretic does not typically cause vasodilation, does not stimulate aldosterone production, does not significantly stimulate Na+ reabsorption and is not stimulated by AII. It does increase water but not ion reabsorption in the kidneys. Therefore, only the claim in e. is entirely correct.

Step-by-step solution

Identify the role of ADH in vasodilation of blood vessels

Antidiuretic hormone (ADH) does not typically cause vasodilation of blood vessels. Instead, it can lead to vasoconstriction, helping to raise blood pressure when needed. Answer a. is therefore incorrect.

Evaluate the statement on ADH stimulating aldosterone

ADH does not stimulate the production of aldosterone. Aldosterone is regulated primarily by the renin-angiotensin system and blood potassium levels. Therefore, answer b. is not correct.

Consider the claim of ADH stimulating reabsorption of Na+ and water

While ADH does play a key role in water re-absorption from the kidneys, it does not have a significant effect on the reabsorption of sodium (Na+). So, answer c. is partially correct but not entirely accurate.

Evaluate the assertion about ADH and AII stimulation

AII (Angiotensin II) does not directly stimulate the release of ADH. Its prominent role is to stimulate the release of aldosterone. Therefore, claim d. is not correct.

Analyze the statement on ADH and ion reabsorption

ADH is crucial for the reabsorption of water in kidneys. It increases water permeability in the collecting ducts of the kidneys. However, it does not contribute to ion reabsorption. So, answer e. correctly describes the function of ADH.

Key concepts

Vasoconstriction

Vasoconstriction is the process where blood vessels narrow down. This narrowing increases blood pressure by making it more difficult for blood to pass through the vessels. Antidiuretic Hormone (ADH), also known as vasopressin, plays a significant role in vasoconstriction.
This process is essential when the body needs to increase blood pressure, such as during dehydration or blood loss. It ensures that blood continues to circulate effectively, delivering oxygen and nutrients to vital organs.

• ADH makes the muscle cells in the vessel walls contract.
• As the diameter of the vessels decreases, blood flow becomes more restricted.

In summary, ADH's ability to cause vasoconstriction is crucial for maintaining stable blood pressure and for ensuring adequate perfusion of tissues under certain physiological conditions.

Aldosterone

Aldosterone is a hormone secreted by the adrenal glands. Its primary function is to regulate sodium and potassium levels in the blood.
By managing these electrolytes, aldosterone plays a crucial role in controlling blood pressure and fluid balance in the body. It achieves this by signaling the kidneys to reabsorb more sodium and excrete potassium.

• This sodium reabsorption leads to water retention, which increases blood volume and pressure.
• Unlike ADH, aldosterone focuses significantly on sodium balance.

Aldosterone secretion is stimulated by the renin-angiotensin system and high levels of potassium in the blood, making it a vital component of the body's ability to maintain homeostasis.

Water Reabsorption

Water reabsorption is the process by which the body retrieves water from the filtrate in the kidneys back into the bloodstream.
ADH is crucial in this process as it increases the permeability of the kidney's collecting ducts to water, allowing more water to be reabsorbed. When ADH is released, it acts on the kidney's collecting ducts, enhancing the reabsorption of water into the bloodstream.

• This helps maintain adequate hydration levels.
• Consequently, the urine becomes more concentrated.

By facilitating water reabsorption, ADH helps the body conserve water, essential during times of dehydration, ensuring that blood pressure remains stable.

Renin-Angiotensin System

The Renin-Angiotensin System (RAS) is a hormone system that regulates blood pressure and fluid balance.
When blood volume is low, cells in the kidneys release renin. Renin then converts angiotensinogen, produced by the liver, into angiotensin I. This is further converted into angiotensin II, an active form that can raise blood pressure.

• Angiotensin II causes vasoconstriction, narrowing blood vessels to increase blood pressure.
• It also stimulates aldosterone production.

The RAS is significant as it functions alongside ADH and aldosterone to maintain blood pressure and electrolyte balance, making it fundamental for cardiovascular health.