Chapter 17, Problem 1TYR

CRH secretion would not raise the blood concentration of

1. a. ACTH.
2. b. thyroxine.
3. c. cortisol.
4. d. corticosterone.
5. e. glucose.

Summary Introduction

Introduction:

The hypothalamus synthesizes the releasing hormones and inhibitory hormones which control secretion or inhibition of hormones by the anterior pituitary. The hypothalamus secretes six hormones namely thyrotropin-releasing hormone (TRH), gonadotropin-releasing hormone (GnRH), prolactin-inhibiting hormone (PIH), corticotropin-releasing hormone (CRH), growth hormone–releasing hormone (GHRH), and somatostatin. These hormones regulate the synthesis of pituitary hormones (FSH, LH, TSH, ACTH, prolactin, and GH). The pituitary hormones control other endocrine glands.

Answer to Problem 1TYR

Correct answer:

Corticotropin-releasing hormone (CRH) secreted by the hypothalamus would not raise the thyroxine concentration in the blood. Thyrotropin-releasing hormone (TRH) from the hypothalamus promotes the release of thyroxine from the thyroid gland. Therefore, option b is correct.

Explanation of Solution

Justify reasons for the correct statement:

The thyroid follicular cells secrete thyroid hormones (TH) such as triiodothyronine (T3) and thyroxine (T4). The thyroid gland releases TH into the bloodstream. The secretion of thyroxine is not influenced by the CRH.

Option (b) is given as “thyroxine”.

CRH does not raise the thyroxine concentration in the blood.

Hence, option (b) is correct.

Justify reasons for the incorrect statements:

Option (a) is given as “ACTH”.

The hypothalamus releases the CRH, which stimulates the anterior pituitary to secrete adrenocorticotropic hormone (ACTH). Hence, it is a wrong answer.

Option (c) is given as “cortisol”.

CRH stimulates ACTH secretion by the anterior pituitary. ACTH promotes the adrenal cortex to release of cortisol (glucocorticoids). Hence, it is a wrong answer.

Option (d) is given as “corticosterone”.

CRH stimulates ACTH secretion by the anterior pituitary. ACTH promotes the adrenal cortex to release the corticosterone (glucocorticoids). Hence, it is a wrong answer.

Option (e) is given as “glucose”.

The hypothalamus secretes the CRH that stimulates the release of ACTH by the anterior pituitary. ACTH stimulates the adrenal cortex to secrete cortisol and corticosterone (glucocorticoids). Cortisol and corticosterone stimulate the catabolism of fat and protein and promote gluconeogenesis. Thereby, they increase glucose concentration into the blood. Hence, it is a wrong answer.

Hence, options (a), (c), (d), and (e) are incorrect.

Conclusion

CRH raises the concentration of ACTH, cortisol, corticosterone, and glucose in the blood, but not thyroxine.