Clinical Chemistry CH-9: The Hypothalamus and the Pituitary Gland PDF

‫دورة المختبرات الخاصة‬ ‫فرع الكيمياء السريرية‬ ‫ الجزء النظري‬/...

‫دورة المختبرات الخاصة‬ ‫فرع الكيمياء السريرية‬ ‫ الجزء النظري‬/ ‫محاضرات في الكيمياء السريرية‬ Lecture by :MSc. Muhammed Kamil / Faculty of medicine university of Babylon Telegram: https://t.me/BioChemPro Reference: Clinical Chemistry, Ninth Edition, William J. Marshall, Marta Lapsley, Andrew Day, Kate Shipman. Clinical chemistry: CH-9 \The hypothalamus and the pituitary gland The pituitary gland has two parts: 1. Anterior Pituitary (Adenohypophysis): Made up of glandular tissue and secretes several hormones, including trophic hormones that stimulate other endocrine glands. Hormone release is controlled by the hypothalamus, which sends hormones through portal blood vessels to regulate pituitary function. Feedback from target organ hormones regulates both hypothalamic and pituitary hormones. 2. Posterior Pituitary (Neurohypophysis): Originates from neural tissue and functions differently from the anterior pituitary. Growth Hormone (GH): - Structure: GH is a 191-amino acid polypeptide hormone. - Function: Vital for normal growth, indirectly stimulates the liver to produce insulin-like growth factor-1 (IGF-1), and has metabolic effects. - Regulation: Controlled by hypothalamic hormones—GHRH (stimulates release) and somatostatin (inhibits release). IGF-1 provides negative feedback to regulate GH production. - Secretion Patterns: GH is secreted in bursts, particularly during deep sleep. Levels rise during puberty and decline with age. Secretion is stimulated by stress, exercise, and low blood sugar, while increased blood sugar inhibits secretion. - Disorders: - Excess GH: Leads to gigantism in children and acromegaly in adults, often caused by a pituitary tumor. - GH Deficiency: Causes growth retardation in children and can result in fatigue, weakness, and cardiovascular risks in adults. Somatostatin: - A 14-amino acid hypothalamic peptide that inhibits GH secretion. - Inhibits TSH release and affects hormone secretion in the gut and pancreas, including gastrin, insulin, and glucagon. - Tumors that secrete somatostatin can occur in the pancreas, thyroid, and lungs. - Therapeutic Uses: Somatostatin analogues treat acromegaly, inhibit tumor hormone secretion, and control bleeding from esophageal varices. Prolactin: - A 199-amino acid polypeptide hormone primarily involved in lactation and breast development. - High levels inhibit GnRH, affecting ovulation in females and spermatogenesis in males. - Regulation: Controlled by dopamine, which inhibits prolactin release. No specific prolactin-releasing hormone is identified in humans. - Stimuli: Pregnancy, suckling, sleep, meals, exercise, and stress increase prolactin secretion. - Hyperprolactinemia: Can occur due to prolactin-secreting tumors or other pituitary tumors obstructing dopamine inhibition. - Deficiency: Rare, often resulting in failure of lactation. Thyroid-Stimulating Hormone (TSH): - A glycoprotein hormone composed of alpha and beta subunits; the beta-subunit is unique to TSH. - Stimulates the synthesis and secretion of thyroid hormones. - Regulation: TSH secretion is controlled by TRH from the hypothalamus and is inhibited by high thyroid hormone levels (negative feedback). - Disorders: Increased TSH in hypothyroidism; decreased TSH in hyperthyroidism. TSH deficiency can lead to hypothyroidism, while TSH-secreting tumors are rare causes of hyperthyroidism. Question Example: - What are the functions of somatostatin, and how is prolactin secretion regulated? Gonadotrophins (FSH and LH): - Both are glycoproteins with alpha and beta subunits, with the beta-subunit being unique to each hormone. - Regulation: Secreted in response to hypothalamic GnRH, with pulsatile secretion occurring every 90 minutes. Feedback from gonadal steroids modulates this release. - In Males: - LH stimulates testosterone production in Leydig cells, which partially converts to estradiol. Testosterone and estradiol inhibit further LH secretion. - FSH, alongside testosterone, promotes spermatogenesis, and its secretion is inhibited by inhibin. - In Females: - FSH stimulates estrogen production and follicle development during the first phase of the menstrual cycle. - A rise in estrogen triggers a positive feedback loop, leading to a surge in LH and FSH, causing ovulation and corpus luteum formation. Rising estrogen and progesterone later inhibit FSH and LH. - If no conception occurs, hormone levels drop, leading to menstruation and the start of a new cycle. - Disorders: - High FSH and LH levels occur in ovarian failure (e.g., menopause) and azoospermia in males. - Gonadotrophin-secreting tumors are rare, but decreased secretion can lead to secondary gonadal failure. Adrenocorticotrophic Hormone (ACTH): - A polypeptide hormone with a molecular mass of 4.5 kDa, composed of 39 amino acids. - Function: Stimulates adrenal glucocorticoid secretion but does not affect mineralocorticoid secretion. - Regulation: Controlled by corticotrophin-releasing hormone (CRH) from the hypothalamus. ACTH secretion is pulsatile and shows diurnal variation, peaking at around 8:00 a.m. and being lowest at midnight. Stress significantly increases ACTH secretion, while cortisol provides negative feedback inhibition. - Disorders: - Increased ACTH levels can result from pituitary tumors (Cushing's disease) or primary adrenal failure (Addison's disease). - ACTH can also be produced by non-pituitary tumors (ectopic ACTH syndrome). - Excess ACTH: Leads to increased pigmentation due to the melanocyte-stimulating effects of ACTH and other POMC-derived peptides. - Deficiency: Can be isolated or part of generalized pituitary failure. Question Example: - How do FSH and LH regulate reproductive functions in males and females, and what are the effects of abnormal ACTH secretion? The corpus luteum: is a temporary endocrine structure in the female reproductive system that forms in the ovary after ovulation. It develops from the ruptured Graafian follicle that released an egg during the ovulation phase of the menstrual cycle. The corpus luteum primarily secretes two hormones: 1. Progesterone: This hormone prepares the lining of the uterus (endometrium) for potential implantation of a fertilized egg and supports early pregnancy. 2. Estrogen: Though produced in smaller amounts compared to progesterone, it also helps maintain the uterine lining.  If fertilization and implantation occur, the corpus luteum continues to produce progesterone until the placenta takes over hormone production. If pregnancy does not occur, the corpus luteum degenerates into a structure called the corpus albicans, leading to a decrease in progesterone and estrogen levels, which triggers menstruation and the start of a new cycle. 40 questions with their answers : 1. What are the two parts of the pituitary gland? - The anterior pituitary (adenohypophysis) and the posterior pituitary (neurohypophysis). 2. What type of tissue is the anterior pituitary composed of? - Glandular tissue. 3. What is the origin of the posterior pituitary? - Neural tissue. 4. How is hormone secretion in the anterior pituitary controlled? - By hormones from the hypothalamus, which are delivered through portal blood vessels. 5. What is the main hormone that stimulates growth? - Growth hormone (GH). 6. What organ does GH primarily target to mediate its effects on growth? - The liver, which produces insulin-like growth factor-1 (IGF-1). 7. What two hormones regulate GH secretion? - Growth hormone-releasing hormone (GHRH) stimulates GH secretion, while somatostatin inhibits it. 8. What condition is caused by excess GH secretion in children? - Gigantism. 9. What condition is caused by excess GH secretion in adults? - Acromegaly. 10. What is the primary function of somatostatin? - To inhibit the secretion of growth hormone (GH). 11. Apart from GH, what other hormone secretion does somatostatin inhibit? - Thyroid-stimulating hormone (TSH), along with several gastrointestinal hormones like gastrin, insulin, and glucagon. 12. What therapeutic use do somatostatin analogues have? - They are used to stop bleeding from esophageal varices, inhibit hormone secretion from tumors, and treat acromegaly. 13. What hormone primarily regulates prolactin secretion? - Dopamine, which inhibits prolactin release. 14. What is the main physiological function of prolactin? - To initiate and sustain lactation. 15. How does prolactin affect reproductive functions in males and females? - High prolactin levels inhibit gonadotropin-releasing hormone (GnRH), thus inhibiting ovulation in females and spermatogenesis in males. 16. What are common stimuli that increase prolactin secretion? - Pregnancy, suckling, sleep, meals, exercise, and stress. 17. What hormone stimulates the synthesis and release of thyroid hormones? - Thyroid-stimulating hormone (TSH). 18. How is TSH secretion regulated? - By thyrotrophin-releasing hormone (TRH) from the hypothalamus and negative feedback from circulating thyroid hormones. 19. What condition is characterized by increased TSH secretion? - Primary hypothyroidism. 20. What hormone inhibits the secretion of gonadotrophins (FSH and LH)? - In males, inhibin inhibits FSH secretion during spermatogenesis. 21. What is the primary function of luteinizing hormone (LH) in males? - To stimulate testosterone secretion by Leydig cells in the testes. 22. What is the primary function of follicle-stimulating hormone (FSH) in males? - To stimulate spermatogenesis in the presence of high intratesticular testosterone. 23. How do FSH and LH function in females during the menstrual cycle? - FSH stimulates estrogen production and follicle development, while LH triggers ovulation and the development of the corpus luteum. 24. What triggers the explosive release of LH and FSH in the menstrual cycle? - A positive feedback mechanism caused by rising estrogen levels. 25. What hormone is elevated during menopause? - Follicle-stimulating hormone (FSH). 26. What causes increased gonadotrophin levels in males? - Azoospermia or decreased testosterone secretion. 27. What is the primary function of adrenocorticotrophic hormone (ACTH)? - To stimulate adrenal glucocorticoid secretion. 28. What is the precursor of ACTH? - Proopiomelanocortin (POMC). 29. What is the role of corticotrophin-releasing hormone (CRH)? - To regulate ACTH secretion from the pituitary. 30. What time of day is plasma ACTH concentration typically highest? - Around 8:00 a.m. 31. What hormone provides negative feedback to inhibit ACTH secretion? - Cortisol. 32. What condition results from excessive ACTH secretion by the pituitary? - Cushing's disease. 33. What is the effect of ACTH on skin pigmentation? - It increases pigmentation due to its melanocyte-stimulating action. 34. What is a common cause of decreased ACTH secretion? - Generalized pituitary failure. 35. What hormone regulates testosterone production in males? - Luteinizing hormone (LH). 36. How does inhibin affect FSH secretion in males? - It inhibits FSH secretion during spermatogenesis. 37. What is the main function of estrogen in the female reproductive cycle? - To stimulate follicle development and prepare the body for ovulation. 38. What happens to FSH and LH levels if conception does not occur? - They decline, leading to menstruation and the initiation of a new cycle. 39. What causes primary adrenal failure (Addison's disease)? - Decreased production of adrenal hormones, leading to increased ACTH secretion. 40. What are the effects of ACTH-secreting tumors outside the pituitary? - They can lead to ectopic ACTH syndrome, causing symptoms similar to Cushing's disease. THE END