Which of the following is the main activating factor of aldosterone secretion during periods of dehydration ?

Options

A. ACTH
B. Sympathetic nervous system
C. Renin
D. Spontaneous adrenal release

Answer

**Step-by-Step Solution:**

1. **Understanding Dehydration**: Dehydration refers to a state where there is a significant loss of water from the body, leading to a decrease in blood volume and an increase in blood concentration.

2. **Role of Aldosterone**: Aldosterone is a hormone that plays a crucial role in regulating blood pressure, blood volume, and the balance of electrolytes (specifically sodium and potassium) in the blood.

3. **Kidney's Response to Dehydration**: When dehydration occurs, the kidneys are the first organs to detect the decrease in blood volume and concentration.

4. **Release of Renin**: In response to dehydration, the kidneys release an enzyme called renin. This is a critical step in the activation of aldosterone secretion.

5. **Formation of Angiotensin**: Renin acts on a protein in the blood called angiotensinogen, converting it into angiotensin I. Angiotensin I is then converted into angiotensin II, which is a potent vasoconstrictor.

6. **Stimulation of Aldosterone Secretion**: Angiotensin II travels to the adrenal glands, specifically the adrenal cortex, where it stimulates the secretion of aldosterone.

7. **Action of Aldosterone**: Aldosterone promotes the reabsorption of sodium (Na+) and water in the kidneys, which helps to restore blood volume and pressure.

8. **Conclusion**: The main activating factor for aldosterone secretion during periods of dehydration is renin, as it initiates the cascade that leads to aldosterone release.

**Final Answer**: Renin is the main activating factor of aldosterone secretion during periods of dehydration.

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