Increase in the excitability of nerves and muscles leading to sustained contraction of the muscles of larynx, face, hand and feet is due to

Options

A. Hyperactivity of thyroid
B. Hyperactivity of parathyroid
C. Hypoactivity of thyroid
D. Hypoactivit of parathyroid

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the cause of increased excitability of nerves and muscles, leading to sustained contraction in specific muscle groups (larynx, face, hands, and feet).

2. **Identifying Key Terms**: The key terms in the question are "excitability of nerves and muscles," "sustained contraction," and "muscles of larynx, face, hand, and feet."

3. **Recognizing the Condition**: The sustained contraction of muscles is often associated with a condition known as tetany. Tetany occurs when there is an abnormal increase in muscle excitability.

4. **Linking to Calcium Levels**: The excitability of nerves and muscles is closely related to calcium levels in the blood. A decrease in blood calcium levels (hypocalcemia) can lead to increased excitability and sustained muscle contractions.

5. **Role of Parathyroid Hormone (PTH)**: The parathyroid glands secrete parathyroid hormone (PTH), which is responsible for regulating calcium levels in the blood. When calcium levels drop, PTH is released to increase blood calcium levels.

6. **Understanding Hypoparathyroidism**: If there is a deficiency or hypoactivity of the parathyroid glands, there will be insufficient PTH produced. This leads to a decrease in blood calcium levels, resulting in the symptoms of tetany, including sustained contractions in the specified muscle groups.

7. **Conclusion**: Therefore, the increase in excitability of nerves and muscles leading to sustained contraction is due to hypoparathyroidism, which causes decreased levels of PTH and subsequently low blood calcium levels.

**Final Answer**: The increase in excitability of nerves and muscles leading to sustained contraction of the muscles of the larynx, face, hand, and feet is due to hypoparathyroidism (hypoactivity of the parathyroid glands).

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