Deficiency of `I_(2)` in diet leads to

Answer

### Step-by-Step Solution:

1. **Understanding the Role of Iodine**:
- Iodine is an essential nutrient that is crucial for the synthesis of thyroid hormones, specifically thyroxine (T4) and triiodothyronine (T3). These hormones are important for regulating metabolism, growth, and development in the body.

2. **Identifying the Hormones Affected**:
- Thyroxine (T4) contains four iodine atoms, while triiodothyronine (T3) contains three iodine atoms. Both hormones require iodine for their production.

3. **Consequences of Iodine Deficiency**:
- When there is a deficiency of iodine in the diet, the thyroid gland is unable to produce adequate amounts of these hormones. This leads to a condition where the body cannot regulate metabolism effectively.

4. **Feedback Mechanism**:
- The pituitary gland senses the low levels of thyroid hormones and responds by releasing more thyroid-stimulating hormone (TSH) to stimulate the thyroid gland. This constant stimulation can lead to an overgrowth of the thyroid tissue.

5. **Resulting Condition - Goiter**:
- The overgrowth of the thyroid gland due to continuous stimulation in the absence of adequate hormone production results in the enlargement of the thyroid gland, a condition known as goiter.

### Final Answer:
Deficiency of iodine in the diet leads to the enlargement of the thyroid gland, a condition known as goiter.

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