Hormones of the Hypothalamus and the Pitutary

Hormones of the Hypothalamus and the Pitutary Prof. Dr. Tarik H. Al-Khayat

1 |D e p a r t m e n t O f B i o c h e m i s t r y A T
1- What are trophic hormones?
? Hormones secreted by the anterior pituitary, which influence hormone secretion by other endocrine glands such as thyroid, adrenal cortex, etc., are termed trophic hormones.
? The trophic hormones are, in turn, controlled by the hypothalamus which synthesizes regulatory peptides that are transported by the hypothalamic portal system to the anterior pituitary.
2- Enumerate the factors that regulate secretion of anterior pituitary hormones.
The factors regulating anterior pituitary hormone secretion include the following:
? Stress (physical, mental, emotional or hypoglycemia).
? Increased plasma levels of target cell hormones, which exert feedback inhibition.
? Circadian rhythm: This may be lost in disease states.
? Drugs: For example, L-dopa stimulates GH secretion.
3- Give a brief account of the anterior pituitary hormones.
1. Growth hormone (GH) regulates growth and intermediary metabolism. GH secretion is stimulated by growth hormone releasing hormone (GHRH), and inhibited by growth hormone release inhibiting hormone (GHRIH) or somatostatin.
2. Thyroid-stimulating hormone (TSH) regulates thyroid function. TSH secretion is stimulated by thyrotropin releasing hormone (TRH).
3. Adrenocorticotrophic hormone (ACTH) stimulates glucocorticoid synthesis, and secretion from the adrenal cortex. It is regulated by corticotrophin-releasing hormone (CRH) from the hypothalamus.
4. Luteinizing hormone (LH) plays a role in ovulation, progesterone synthesis, and testosterone production. It is under the control of hypothalamic gonadotrophin-releasing hormone (GnRH).
5. Follicle-stimulating hormone (FSH) regulates estrogen synthesis, oogenesis, and spermatogenesis. It is regulated by GnRH.
6. Prolactin acts on the mammary gland to induce lactation. It is regulated by prolactin-release inhibiting hormone (PRIH), and TSH.
7. ?-Lipotrophin is a neurotransmitter and endorphin precursor that is regulated by CRH.