Menstrual Cycle and Reproductive Hormones Quiz

Reproductive Endocrinology

• Recommended Reading:
• Rang and Dales Pharmacology - Chapter 34
• Tortora and Derrickson's Anatomy and Physiology - Chapter 28
• Practice MCQ questions: Available on Moodle
• Topics to cover:
• Hormonal regulation of the male reproductive system
• Hormonal regulation of the female reproductive system
• Contraceptive pill
• Reproductive pathology and treatment
• Pregnancy/birth/lactation
• Teratogens

Male Reproductive System

• Leydig Cells: Located between seminiferous tubules, secrete testosterone.
• Sertoli Cells: Embedded with spermatogenic cells in the tubules; form blood testes barrier, nourish spermatocytes, mediate effects of testosterone and FSH on spermatogenesis, and phagocytose excess spermatids. Secretes inhibin which regulates sperm production by inhibiting FSH production.
• Hormonal Control of Spermatogenesis:
• GnRH (gonadotropin-releasing hormone): Main hormone, stimulates the anterior pituitary to secrete FSH and LH.
• FSH (follicle-stimulating hormone): Stimulates spermatogenesis
• LH (luteinizing hormone): Stimulates testosterone secretion (also called interstitial cell-stimulating hormone, ICSH, in the male).
• Testosterone and DHT (dihydrotestosterone): 5α-reductase converts Testosterone to DHT, DHT is responsible for development of external genitalia and prostate.
• Inhibin: Helps to regulate sperm production by inhibiting FSH.
• Control of Testosterone Production:
• Negative feedback system controls blood levels of testosterone.
• Receptors in hypothalamus detect increased blood level of testosterone.
• Inhibits secretion of GnRH from hypothalamus.
• Reduced secretion of LH from anterior pituitary.
• Leydig cells secrete less testosterone.
• Blood level returns normal.
• Male Hypogonadism: (disorders of hormone production by the testes).
• Primary congenital: Testicular agenesis (failure), Klinefelter syndrome (47XXY)
• Primary acquired: Bilateral orchitis (inflammation of testes)
• Secondary: Pituitary disorders, hypothalamic disorders (e.g., Kallman's syndrome - GnRH deficiency).
• Aging in the male reproductive system: Enlargement of prostate (benign hyperplasia) in ⅓ of males over 60
• Prostate Cancer: Leading male cancer death. Blood test for prostate-specific antigen (PSA). Antiandrogens (e.g., flutamide, cyproterone) used in treatment to block testosterone/DHT actions, preventing stimulation of prostate cancer growth.
• Erectile Dysfunction Treatment: Viagra (Sildenafil citrate) – PDE5 inhibitor.

Female Reproductive System

• The Female Reproductive Cycle: Encompasses ovarian and uterine cycle, hormonal changes regulating them, and changes in breasts and cervix. Controlled by monthly hormone cycle of anterior pituitary, hypothalamus, and ovary.
• Ovarian cycle: Changes in ovaries during and after oocyte maturation.
• Uterine (menstrual) cycle: Concurrent series of changes in uterine endometrium preparing for fertilized ovum arrival. If not fertilized, stratum functionalis shed during menstruation.
• Hormonal control of the female reproductive cycle:
• GnRH (gonadotropin-releasing hormone): Secreted by hypothalamus, controls ovarian and uterine cycle, stimulates release of FSH and LH from anterior pituitary.
• FSH (follicle-stimulating hormone): Initiates follicular growth, stimulates ovarian follicles to secrete estrogens.
• LH (luteinizing hormone): Stimulates further development of ovarian follicles, stimulates ovarian follicles to secrete estrogen, triggers ovulation. Prompts the formation of corpus luteum; produces estrogens, progesterone, relaxin, and inhibin.
• Ovarian hormones:
• Estrogens (mainly β-estradiol): Secreted by ovarian follicles. Promotes female reproductive structures and secondary sex characteristics, increases protein anabolism (building strong bones), lowers blood cholesterol, inhibits GnRH, LH, and FSH release.
• Progesterone: Secreted mainly by corpus luteum. Works with estrogens to prepare and maintain endometrium for implantation and mammary glands for milk production, inhibits GnRH and LH secretion.
• Relaxin: Produced by corpus luteum. Relaxes uterus by inhibiting myometrium contraction. Increases pubic symphysis flexibility and dilates uterine cervix at end of pregnancy.
• Inhibin: Secreted by granulosa cells of growing follicles. Inhibits FSH and LH secretion.
• Secretion and physiological effects of hormones in the female reproductive cycle: (detailed description of hormonal interactions and their effects)
• Phases of the female reproductive cycle: Menstrual, pre-ovulatory, ovulation, post-ovulatory.
• Corpus Luteum: If not fertilized, lasts 2 weeks. Degenerates into corpus albicans and decreases progesterone, estrogens, and inhibin, and releases GnRH, FSH, and LH. If fertilized, hCG (human chorionic gonadotropin) is produced by chorion that stimulates further production of progesterone and estrogens, and the cycle continues.
• Postovulatory phase (days 15-28) – Secratory Phase:
• Progesterone and estrogen produced by corpus luteum promote endometrial growth.
• If fertilization doesn't occur, levels of progesterone and estrogen decline causing menstruation.
• Hormonal Interactions in the ovarian and uterine cycles: (detailed description of feedback loops)
• Causes of female hypogonadism:
• Primary congenital: Turner syndrome (45XO), Noonan syndrome (46XX)
• Primary acquired: Chemotherapy, irradiation
• Secondary (indirect): Pituitary disorders, hypothalamic disorders
• Treatment: Clomiphene
• Aging in the female reproductive system: Menopause (hot flushes, vaginal dryness, depression). Treatment for short term (2–5 years) includes HRT (estrogen/progesterone) such as Tibolone. Drawbacks of long-term HRT include increased cancer risk.
• Endometriosis: Growth of endometrial tissue outside the uterus, GnRH analogues (buserelin) prevent estrogen production, progesterone (medroxyprogesterone acetate), Danazol.
• Breast Cancer: Leading cause of cancer in UK, genes BRCA1 and BRCA2 increases susceptibility, hormone therapy/lumpectomy/mastectomy/radiation treatment treatment options.

Teratogens

• Definition: Substances affecting fetal development
• Chemicals and Drugs: Thalidomide, Warfarin, Corticosteroids, Stilbestrol, Phenytoin, Valproate, Carbamazepine, Cytotoxic drugs (methotrexate), Aminoglycosides, Tetracyclines, Ethanol, Retinoids.
• Mechanism: Affects different stages of gestation (blastocyst formation, organogenesis, maturation).
• Effects: Specific effects on the fetus vary based on the teratogen. Can include phocomelia (limb malformation), heart defects, cleft palate, mental retardation, and other developmental abnormalities.

Pregnancy and Labor

• Hormonal changes during pregnancy: Human chorionic gonadotropin (hCG) rescues corpus luteum and maintains estrogen and progesterone production, human placental lactogen (hPL), and cortisol are also important.
• Labor (Parturition): Progesterone prevents uterine contractions, corticotropin-releasing hormone (CRH) secretion increases, and oestrogen levels overcome progesterone, inducing prostaglandin release.
• Contractions (positive feedback mechanism): Oestrogen and relaxin soften the cervix. Activation of stretch receptors in the cervix increases oxytocin release from posterior pituitary resulting in contraction of uterine muscles and pushing the baby towards the cervix. Positive feedback loop.
• Lactation (milk secretion and ejection): Prolactin produced by anterior pituitary, but progesterone inhibits prolactin effects. Suckling stimulates nerve impulses released from stretch receptors in the nipples leading to hypothalamic release of prolactin-releasing hormone (PRH), which increases prolactin further increasing milk secretion. Oxytocin stimulates contraction of myoepithelial cells in breasts, squeezing the ducts and causing milk secretion.

Contraceptives

• Combined Pill: Oestrogen inhibits FSH and follicle development, and progesterone inhibits LH preventing ovulation and makes cervical mucus inhospitable for sperm, together making endometrium unsuitable for implantation.
• Progesterone-only Pill: Makes cervical mucus inhospitable for sperm, inhibits ovulation by reducing LH.
• Morning-after Pill: Effective within 72 hours; either combined or progestin-only pills; inhibits FSH and LH, reducing oestrogen and progesterone in the ovary.

Additional Notes

• The provided material covers a wide variety of topics related to reproductive endocrinology. Each topic requires detailed study to fully understand the mechanisms, interactions, and examples mentioned.

Test your knowledge on the roles of hormones in the menstrual cycle and male reproductive system. This quiz covers the effects of estrogen and progesterone, as well as the functions of GnRH, Sertoli cells, and testosterone production. Explore the complexities of reproductive hormones and their impacts.