Correct Option
The correct option is 1 and 3 only.
Explanation
Aldosterone is the primary mineralocorticoid hormone produced by the outer section (zona glomerulosa) of the adrenal cortex in the adrenal gland. It plays a critical role in regulating the balance of electrolytes (sodium and potassium) and water in the body, thereby influencing blood volume and blood pressure.
Statement-wise Analysis
- Statement 1 is Correct: Aldosterone acts mainly on the renal tubules, specifically the distal convoluted tubule and the collecting duct. It stimulates the reabsorption of sodium ions (Na+) and water from the filtrate back into the blood. This conservation of sodium and water is essential for maintaining body fluid volume.
- Statement 2 is Incorrect: While aldosterone promotes the retention of sodium, it simultaneously stimulates the excretion (secretion) of potassium (K+) and phosphate ions into the urine. Therefore, it reduces the retention of potassium and phosphate in the body rather than increasing it.
- Statement 3 is Correct: By promoting the reabsorption of sodium and water, aldosterone increases the total blood volume. An increase in blood volume leads to an increase in blood pressure. This function is a key component of the Renin-Angiotensin-Aldosterone System (RAAS), which regulates systemic blood pressure.
Key Takeaway
Key Takeaway: Aldosterone acts on the kidneys to conserve sodium and water (increasing blood pressure) while promoting the excretion of potassium and phosphate ions.