Question

medullary carcinoma of the thyroid gland will result in:
○ a decrease in calcitonin production.
○ a compensatory parathyroid hyperplasia.
○ an increase in thyroid hormone production.
○ hypercalcemia

Explanation:

1. Recall the role of calcitonin (produced by thyroid C - cells, which are the origin of medullary carcinoma) and its effect on calcium: Calcitonin lowers blood calcium by inhibiting osteoclasts and promoting calcium deposition in bones.
2. Analyze each option:

• Option 1: Medullary carcinoma arises from C - cells. In medullary carcinoma, C - cells can overproduce calcitonin (not decrease), so this is incorrect.
• Option 2: Parathyroid hyperplasia is not a typical direct result of medullary thyroid carcinoma. Medullary carcinoma is related to C - cells and calcitonin, not direct parathyroid compensation in this way, so this is incorrect.
• Option 3: Medullary carcinoma is from C - cells, not the follicular cells that produce thyroid hormones (T3, T4). So it does not lead to increased thyroid hormone production, incorrect.
• Option 4: If calcitonin production is disrupted (in medullary carcinoma, sometimes there can be abnormal regulation, or if calcitonin is not functioning properly to lower calcium), or if there are other factors, but more importantly, the normal function of calcitonin is to lower calcium. If the tumor affects the normal regulation, and considering the relationship between calcitonin and calcium, when calcitonin's action is impaired (or in some cases, the tumor may be associated with other factors), hypercalcemia can occur. Also, medullary thyroid carcinoma can be associated with multiple endocrine neoplasia syndromes which may have other hormonal imbalances leading to hypercalcemia. Alternatively, if the C - cell tumor is not producing enough functional calcitonin to lower calcium, blood calcium levels rise (hypercalcemia).

Answer:

D. hypercalcemia (assuming the options are labeled A - D as: A. a decrease in calcitonin production, B. a compensatory parathyroid hyperplasia, C. an increase in thyroid hormone production, D. hypercalcemia)