Water and electrolyte balance in the body is a tightly regulated process essential for maintaining blood pressure, blood volume, and overall homeostasis. Two crucial hormones, aldosterone and antidiuretic hormone (ADH), work together to modulate sodium and water reabsorption in the kidneys, responding to dietary intake and hydration status.

Scenario Overview

A boy consumes a large portion of cheese, rich in sodium, but drinks hardly any fluids. Despite this, his water and electrolyte balance remains maintained. This scenario indicates efficient homeostatic adjustments by the body, involving hormonal responses.

Role of Aldosterone

• Aldosterone is secreted by the adrenal cortex and promotes sodium reabsorption in the distal tubules and collecting ducts of the kidney.

• By increasing sodium retention, aldosterone indirectly promotes water retention as water follows sodium osmotically.

• When sodium intake is high, aldosterone secretion generally decreases to avoid excessive sodium retention and fluid overload.

• However, in this case, because fluid intake is minimal, the body may adjust aldosterone levels to balance both sodium and water retention efficiently.wikipedia+1

Role of Antidiuretic Hormone (ADH)

• ADH, also called vasopressin, regulates water reabsorption by increasing the permeability of the kidney’s collecting ducts to water.

• ADH binds to V2 receptors in principal cells, triggering insertion of aquaporin-2 water channels into the apical membrane, enhancing water reabsorption.

• In scenarios of low fluid intake or high plasma osmolarity (due to high sodium), ADH secretion increases to conserve water despite high sodium load.study+1

Coordinated Hormonal Response in the Scenario

• Aldosterone is decreased to prevent excessive sodium retention in light of high sodium intake.

• ADH is increased to promote water reabsorption despite low fluid intake, maintaining osmolarity and hydration status.

• This combined action ensures plasma sodium concentration and volume remain stable.

Why the Other Options Are Less Likely

• Increased aldosterone and decreased ADH (option 2) would cause sodium retention but insufficient water conservation.

• No change in either hormone (option 3) would fail to compensate for the high sodium intake and low fluid intake.

• Sympathoadrenal system stimulation (option 4) is not the primary mechanism in this context.

Conclusion

The correct and physiologically consistent explanation for maintained water and electrolyte balance in this boy is:

(1) His aldosterone was decreased and ADH was increased.