Question

Given below are two statements:
Statement (I): If thyroid gland secret insufficient quantity of thyroxin hormone the condition is called hypothyroidism.
Statement (II): In hypothyroidism thyroid stimulating hormone concentration in the blood is also below normal.
In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both Statement I and Statement II are correct
• B. Both Statement I and Statement II are incorrect
• C. Statement I is correct but Statement II is incorrect
• D. Statement I is incorrect but Statement II is correct

Hint:

Remember the feedback loop:
Low Thyroid Hormones ($\text{T}_4/\text{T}_3$) $\rightarrow$ Pituitary loses its "brakes" $\rightarrow$ TSH spikes high.
This is why a high TSH test is the hallmark diagnostic finding for primary hypothyroidism.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The thyroid gland synthesizes and secretes thyroid hormones (thyroxine, T4, and triiodothyronine, T3).
This secretion is regulated by a classic negative feedback loop involving the hypothalamus (TRH) and the anterior pituitary gland (TSH).

Step 2: Detailed Explanation:
Let us evaluate each statement individually:
- Statement (I): If the thyroid gland secretes an insufficient quantity of thyroxin hormone, the condition is called hypothyroidism.
This is correct. Hypothyroidism is the clinical state resulting from underproduction of thyroid hormones, causing a generalized slowing of metabolic processes.
- Statement (II): In hypothyroidism, thyroid stimulating hormone (TSH) concentration in the blood is also below normal.
This is incorrect for primary hypothyroidism, which accounts for $>95\%$ of clinical cases.
In primary hypothyroidism, the thyroid gland itself is diseased or dysfunctional and cannot produce T4/T3.
Because T4 and T3 levels are low, there is a lack of negative feedback inhibition on the pituitary gland.
The pituitary responds by synthesizing and secreting highly elevated amounts of TSH to stimulate the thyroid.
Therefore, in primary hypothyroidism, TSH levels in the blood are significantly above normal (elevated), which serves as the primary diagnostic indicator for the condition.
(Only in rare secondary hypothyroidism due to pituitary failure would TSH be below normal).

Step 3: Final Answer:
Therefore, Statement I is correct but Statement II is incorrect, corresponding to option (C).