Predicted Levels for TRH, TSH, and Thyroid Hormone

by | Sep 14, 2024 | biology

 

Patient Z tends to be hyperactive and thin. You are an endocrinologist, and you first determine that Z has high thyroid hormone levels in the blood. Your next step is to determine whether the problem lies at the level of the hypothalamus, anterior pituitary or the thyroid gland. What is the predicted level (high, normal, low) for TRH, TSH and thyroid hormone if the problem is:

a) due to a problem with secretion of TRH by the hypothalamus?

b) due to a problem with secretion of TSH by the anterior pituitary gland?

c) due to a problem with secretion of thyroid hormone by the thyroid gland?

Use this framework for your answer:

Condition a) (hypothalamus defect)
TRH levels:

TSH levels:

thyroid hormone levels:

Condition b) (anterior pituitary defect)
TRH levels:

TSH levels:

thyroid hormone levels:

Condition c) (defect at the level of the thyroid gland)
TRH levels:

TSH levels:

Thyroid hormone levels:

Assume that you determine that the problem is high secretion of TSH by the anterior pituitary, despite normal levels of TRH. Describe two possible causes of this problem, and how you could gather evidence for those causes. Assume that you can take small pieces of Xs anterior pituitary gland, keep it alive in a dish, and measure what you need to measure.

Possible cause #1 for high secretion of TSH by the anterior pituitary despite normal TRH:
Experimental evidence that would support this cause: (1 pt).
Possible cause #2 for high secretion of TSH by the anterior pituitary despite normal TRH:
Experimental evidence that would support this cause:

 

Predicted Levels for TRH, TSH, and Thyroid Hormone

Condition a) (Hypothalamus defect)

– TRH levels: Low
– TSH levels: Low
– Thyroid hormone levels: Low

Explanation: If there is a defect in the hypothalamus, TRH (Thyrotropin-Releasing Hormone) secretion would be decreased. This reduction would lead to lower levels of TSH (Thyroid-Stimulating Hormone) from the anterior pituitary and consequently lower thyroid hormone levels.

Condition b) (Anterior pituitary defect)

– TRH levels: Normal
– TSH levels: Low
– Thyroid hormone levels: Low

Explanation: In the case of an anterior pituitary defect, TRH levels would remain normal because the hypothalamus is functioning correctly. However, since the anterior pituitary is unable to secrete TSH effectively, TSH levels would be low, leading to low levels of thyroid hormones as well.

Condition c) (Defect at the level of the thyroid gland)

– TRH levels: Normal
– TSH levels: Normal
– Thyroid hormone levels: High

Explanation: If the defect lies within the thyroid gland itself, the gland may be secreting excessive amounts of thyroid hormones independent of TSH stimulation. TRH and TSH levels would remain normal because they are being produced adequately by the hypothalamus and anterior pituitary, respectively.

Possible Causes of High Secretion of TSH by the Anterior Pituitary Despite Normal TRH

Possible cause #1 for high secretion of TSH by the anterior pituitary despite normal TRH:
Hyperplasia or tumor of the anterior pituitary gland (e.g., a TSH-secreting adenoma) could lead to increased production of TSH independently of TRH levels.

Experimental evidence that would support this cause:
Histological examination of the anterior pituitary tissue could reveal an excess of TSH-secreting cells or a tumor. Additionally, measuring TSH production in vitro from cultured anterior pituitary cells would show elevated levels compared to normal controls.

Possible cause #2 for high secretion of TSH by the anterior pituitary despite normal TRH:
Resistance to negative feedback by thyroid hormones due to mutations in thyroid hormone receptors or other signaling pathways could lead to increased TSH secretion as the anterior pituitary perceives low thyroid hormone action.

Experimental evidence that would support this cause:
Performing receptor binding assays on anterior pituitary cells could demonstrate decreased binding efficacy of thyroid hormones to their receptors. Additionally, measuring downstream signaling responses (such as cAMP levels) in response to normal thyroid hormone concentrations could show blunted responses, indicating receptor resistance.

 

 

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