Problem 125 - Objective Biology for NEET

Question

Assertion: Aldosterone increases the volume of blood and other extracellular fluids. Reason: The secretion of aldosterone is stimulated by a fall in the circulating volume of blood.

Step-by-Step Solution

Answer

Yes, the assertion and reason are correct. Aldosterone does increase the volume of blood and other extracellular fluids and its secretion is indeed stimulated by a fall in the circulating volume of blood. These two processes are part of a complex system which maintains homeostasis in the body.

Step 1: Understand Aldosterone's Function

Aldosterone is a hormone produced in the adrenal cortex. It plays a vital role in the regulation of blood pressure. More specifically, it acts on the cells of the kidney to cause sodium retention and potassium excretion. As a result, water follows the sodium (due to osmosis), leading to an increase in blood and extracellular fluid volumes.

Step 2: Understand The Trigger For Aldosterone Secretion

Aldosterone secretion is stimulated by various signals. One of the most significant triggers is a decrease in blood volume. When blood volume falls, the kidneys release the enzyme renin, which initiates a series of reactions resulting in the production of a molecule called angiotensin II. Angiotensin II stimulates the adrenal cortex to produce and release aldosterone.

Step 3: Connect the Function and Trigger of Aldosterone

When there is a fall in the volume of blood circulating in the body, more aldosterone is secreted. This aldosterone will cause the kidney to retain more sodium and water, subsequently restoring and increasing the blood volume. Thus, the assertion and the reason given can be linked logically since the function of aldosterone (to increase blood volume) would be triggered by the described condition (a decrease in blood volume).

Key Concepts

Adrenal Cortex

The adrenal cortex is a vital part of our body's adrenal glands, which are located on top of each kidney.
These glands produce a variety of hormones, including aldosterone.
Aldosterone is crucial for maintaining blood pressure and electrolyte balance.
The adrenal cortex itself has three layers, each responsible for producing different hormones.

• The outer layer produces mineralocorticoids like aldosterone.
• The middle layer produces glucocorticoids.
• The inner layer produces androgens.

Understanding the functioning of the adrenal cortex helps grasp why aldosterone is so important for regulating blood pressure.

Blood Volume Regulation

Blood volume regulation is an essential process that ensures our organs and tissues receive adequate oxygen and nutrients.
It involves a delicate balance of fluid intake and retention, largely controlled by hormones like aldosterone.
When blood volume decreases, mechanisms in the body signal for more aldosterone production.
This hormone helps retain sodium, leading water to follow and increase blood and extracellular fluid volumes.
Several external factors can affect blood volume, such as hydration status and sodium intake.
Maintaining balance is essential for health and wellbeing.

Renin-Angiotensin System

The renin-angiotensin system (RAS) is a complex hormonal system that plays a critical role in blood pressure regulation and fluid balance.
It begins with the release of the enzyme renin from the kidneys in response to low blood volume or pressure.

• Renin converts angiotensinogen, a protein from the liver, into angiotensin I.
• Angiotensin I is then converted to angiotensin II, primarily in the lungs.
• Angiotensin II is a potent vasoconstrictor and stimulates the adrenal cortex to release aldosterone.

This chain of reactions helps increase blood pressure and volume, vital for ensuring proper circulation.

Kidney Function

Kidneys are vital organs performing crucial functions such as filtering blood, eliminating waste, and maintaining fluid and electrolyte balance.
Their function is tightly linked to hormones like aldosterone.
Aldosterone acts mainly on the distal tubules and collecting ducts of the kidneys.

• It promotes sodium reabsorption, which is followed by water through osmosis.
• It also increases potassium excretion, which is essential for electrolyte balance.

Through these processes, kidneys help manage blood pressure and the volume of blood and extracellular fluids.

Sodium Retention

Sodium retention is a critical bodily process that helps maintain fluid balance and blood pressure.
Aldosterone plays a significant role in sodium retention by signaling the kidneys to reabsorb sodium.

• When sodium is reabsorbed, water follows, leading to increased blood volume through osmosis.
• This process is vital during situations where blood volume is low, such as dehydration or blood loss.

Efficient sodium retention prevents excessive fluid loss and helps keep the body's internal environment stable.