Question

Hi, please include a detailed answer for both parts of this question, thanks!

1 A) Identify the changes in TSH and TRH secretion that you would expect to see in a patient with hypothyroidism due to iodine deficiency. (1 mark-50-100 words)

1 B) Using your knowledge of thyroid hormone regulation, explain why you would see these changes in TSH and TRH secretion. (2 marks-150-200 words)

Answer 1

1. A) In a patient of hypothyroidism due to iodine deficiency, the production of TSH and TRH will increase.

Explanation: - TRH (thyrotropin-releasing hormone) is produced by hypothalamus which travels to the anterior pituitary gland through hypophyseal portal system and stimulates the production of TSH (thyroid stimulating hormone).

- TSH acts on the thyroid gland and stimulates the production of thyroid hormones (T3 and T4) that helps in controlling the metabolism of the body. Iodine is essential for the production of thyroid hormones and in cases of deficiency of iodine in the diet the production of thyroid hormones is impaired resulting in hypothyroidism which is accompanied with an enlargement of thyroid gland known as goitre.

- In cases of goitre (hypothyroidism), there is decreased level of thyroid hormones in the body which stimulates the hypothalamus to secrete more TRH (thyrotropin-releasing hormone) which in turn increases the secretion of TSH (thyroid stimulating hormone) from the anterior pituitary gland. The increased TSH stimulates the thyroid gland to synthesize more thyroid hormones thus bringing back the level of thyroid hormones to normal range.

1. B) - In case of hypothyroidism due to iodine deficiency, TSH and TRH levels will rise in an attempt to increase the synthesis of thyroid hormones (T3 and T4).

- The level of thyroid hormones is maintained in an optimum range due to feedback mechanism between the production of TRH from hypothalamus, TSH from anterior pituitary gland and thyroid hormones from thyroid gland.

- When there is decreased level of thyroid hormones in the blood, the hypothalamus increases the production of TRH which increases the production of TSH from anterior pituitary gland which in turn increases the synthesis of thyroid hormones from thyroid follicles. Thus, the body tries to maintain the level of thyroid hormones in cases of hypothyroidism by increasing the secretion of TRH and TSH that increases the synthesis of thyroid hormones.

- In cases of increased level of thyroid hormones in the blood, the hypothalamus reduces the production of TRH which reduces the secretion of TSH from anterior pituitary gland which in turn reduces the synthesis of thyroid hormones. This is an example of negative feedback mechanism.