Question

If a person performing heavy physical work in summer becomes dehydrated due to excessive sweating and low water intake, which of the following changes will occur to maintain the proper water level in the blood?

• A. Increase in ADH secretion \(\rightarrow\) Increased water reabsorption in distal tubule & collecting duct \(\rightarrow\) Formation of concentrated urine.
• B. Increase in ADH secretion \(\rightarrow\) Decreased water reabsorption in distal tubule & collecting duct \(\rightarrow\) Formation of concentrated urine.
• C. Decrease in ADH secretion \(\rightarrow\) Increased water reabsorption in distal tubule & collecting duct \(\rightarrow\) Formation of dilute urine.
• D. Decrease in ADH secretion \(\rightarrow\) Decreased water reabsorption in distal tubule & collecting duct \(\rightarrow\) Formation of concentrated urine.

Hint:

Loss of water raises blood osmolarity and triggers more ADH.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept
Heavy sweating with little water intake raises blood osmolarity. Osmoreceptors in the hypothalamus detect this.

Step 2: Hormonal response
The posterior pituitary releases more ADH (vasopressin).
ADH makes the distal tubule and collecting duct more permeable to water.

Step 3: Result
More water is reabsorbed into the blood. A small volume of concentrated urine is passed.

Step 4: Why the other options fail
Decreased ADH or decreased reabsorption would lose more water and worsen dehydration.

Final Answer:
ADH increases, water reabsorption increases and concentrated urine is formed. \[ \boxed{\text{(A) }\text{Increase in ADH secretion }\rightarrow\text{ Increased water reabsorption in distal tubule \& collecting duct }\rightarrow\text{ Formation of concentrated urine.}} \]