All the following is true about control of secretion if TSH except:
a) It is inhibited by T4
b) It is increased in cold weather
c) It is increased in Grave's disease
d) It is increased in TRH
e) Has no marked diurnal rhythm
e) Has no marked diurnal rhythm
To answer this question, we need to determine which statement is incorrect regarding the control of secretion of thyroid-stimulating hormone (TSH). Let's analyze each option:
a) It is inhibited by T4: TSH secretion is regulated through a negative feedback mechanism. When there are high levels of thyroid hormones, such as T4, in the blood, they inhibit the release of TSH from the pituitary gland. This statement is true.
b) It is increased in cold weather: Cold weather stimulates the release of thyrotropin-releasing hormone (TRH) from the hypothalamus, which, in turn, stimulates the secretion of TSH. Therefore, TSH secretion is increased in cold weather. This statement is true.
c) It is increased in Grave's disease: Grave's disease is an autoimmune condition where the body produces autoantibodies that stimulate the thyroid gland to produce excessive amounts of thyroid hormones. As a result, the levels of TSH become suppressed in Grave's disease. Therefore, this statement is incorrect.
d) It is increased in TRH: TRH is released from the hypothalamus and acts on the pituitary gland to stimulate the secretion of TSH. So, TSH levels increase in response to TRH. This statement is true.
e) Has no marked diurnal rhythm: Diurnal rhythm refers to a pattern that follows a daily cycle. In the case of TSH, its secretion is highest during the night and early morning, then gradually decreases throughout the day. Therefore, TSH does have a marked diurnal rhythm, and this statement is incorrect.
In conclusion, the incorrect statement about the control of secretion of TSH is:
c) It is increased in Grave's disease.
The correct answer is:
d) It is increased in TRH
Control of secretion of Thyroid Stimulating Hormone (TSH) is not directly increased by TRH (Thyrotropin-Releasing Hormone). TSH is controlled by negative feedback mechanisms that involve the hypothalamus, pituitary gland, and thyroid gland.
Here are the explanations for the other options:
a) It is inhibited by T4: This statement is true. TSH secretion is inhibited by the hormone T4 (thyroxine) which is produced by the thyroid gland. T4 inhibits the release of TSH through negative feedback.
b) It is increased in cold weather: This statement is true. Cold weather stimulates the release of Thyrotropin-Releasing Hormone (TRH) from the hypothalamus, which leads to increased secretion of TSH from the pituitary gland. This, in turn, stimulates the thyroid gland to increase thyroid hormone production, which helps regulate body temperature.
c) It is increased in Grave's disease: This statement is true. Grave's disease is an autoimmune disorder that causes the overproduction of thyroid hormones. In this condition, autoantibodies bind to and stimulate the thyroid-stimulating hormone receptor, leading to increased secretion of TSH and excessive production of thyroid hormones.
e) Has no marked diurnal rhythm: This statement is false. TSH secretion does have a marked diurnal rhythm, with higher levels during the night and lower levels during the day. The secretion of TSH is influenced by the circadian rhythm and is regulated by the hypothalamus and pineal gland.
Remember, the correct answer is d) It is increased in TRH, as TSH secretion is not directly increased by TRH.