MCS - Reproductive Physiology

Female reproductive system - Controlled by monthly hormone cycle of: - hypothalamus - anterior pituitary - ovary - Monthly cycle of changes in ovary and uterus: - Ovarian cycle - Uterine cycle Ovarian cycle Changes in ovary during and after maturation of oocyte. Uterine cycle 1 - Preparation of uterus to receive fertilised ovum. 2 - Shedding of the stratum functionalis during menstruation if implantation does not occur. - Gonadotrophic releasing Hormone (GnRH) secreted by the hypothalamus Hormone regulation of female reproduc- controls the female reproductive cycle. tive cycle - Stimulates anterior pituitary to secret: - Follicle Stimulating Hormone (FSH) - Luteinizing Hormone (LH) Follicle Stimulating Hormone (FSH) - Initiates growth of follicles - Follicles secrete oestrogen - Oestrogen maintains reproductive organs Luteinising Hormone (LH) - Stimulates ovulation - Promotes formation of corpus luteum - Corpus luteum secretes: - oestrogens - maintains reproductive organs. - progesterone - prepares uterus for implantation and the mammary glands for milk secretion. - relaxin - facilitates implantation in the relaxed uterus. 1/5 - inhibin - inhibits the secretion of FSH and LH. Female reproductive phases - Menstrual phase - Preovulatory phase - Ovulation - Postovulatory phase Menstrual phase - Menstruation lasts for 5 days - First day is considered the beginning of the 28 day cycle: - ovary - uterus Menstrual phase: ovary - 20 follicles that began to develop 6 days before are now beginning to secrete oestrogen. - Fluid is filling the antrum from the granulosa cells. - Declining levels of progesterone: - spiral arteries constrict - glandular tissue dies Menstrual phase: uterus - Stratum functionalis layer: - sloughed off - 50 to 150 ml of blood lost Preovulatory phase - Lasts from day 6 to 13. - Most variable timeline. Preovulatory Phase: follicular phase (ovary) - Dominant follicles survive to day 6 - Day 14, graafin follicle has enlarged and bulges at surface - Follicular secretion of oestrogen and inhibin slows secretion of FSH - Increasing oestrogen levels trigger the secretion of LH Preovulatory phase: proliferative phase (uterus) - Increasing oestrogen levels - Repair and thickening of the stratum functionalis - 4-10 mm in thickness 2/5 - Day 14: - rupture of follicle - release of secondary oocyte Ovulation - Cause of ovulation: - increasing levels of oestrogen - stimulates release of GnRH which stimulates anterior pituitary to release more LH - Corpus hemorrhagicum results Signs of ovulation - Increase in basal body temperature - Changes in cervical mucus - Cervix softens - Mittelschmerz pain Postovulatory phase - Most constant timeline - Lasts 14 days Postovulatory phase: ovary (luteal phase) If fertilisation does not occur: - corpus albicans is formed - as oestrogen and progesterone levels drop, secretion of GnRH, FSH and LH rise. If fertilisation did occur: - developing embryo secretes human chorionic gonadotropin (hCG). - maintains health of corpus luteum and its hormone secretions. - Hormones from corpus luteum promote thickening of endometrium to 12-18 mm. Postovulatory Phase: uterus (secretory - Formation of more endometrial glands phase) and vascularisation. - If no fertilisation occurs, menstrual phase will begin. 3/5 Hypothalamus - Gonadotrophic releasing hormone (GnRH) - control of other FSH and LH. Female Gonadotrophic Hormones Anterior pituitary - Follicle stimulation hormone (FSH) - stimulates follicle. Anterior pituitary - Luteinising hormone (LH) - follicle maturation, corpus luteum formation. Female hormones - oestrogen - Follicles - Proliferation of endometrial cells - Mammary gland development - Increase in FSH and LH before ovulation - Decrease in FSH/LH after ovulation - Secondary sexual characteristics Female hormones - progesterone - Corpus Luteum - Hypertrophy of endometrial cells - Mammary gland development - Decrease in FSH/LH after ovulation - Secondary sexual characteristics Hormonal effects of testosterone Testosterone and Dihydrotestosterone (DHT - more potent) bind to receptors in cell nucleus and change gene activity. Prenatal effect is for a male to develop At puberty, final development of 2nd sexual characteristics and adult reproductive system: - sexual behaviour and libido - male metabolism (bone and muscle mass heavier) - deepening of the voice Puberty: - Hypothalamus increases stimulation of Hormonal control of spermatogenesis I anterior pituitary with Gonadotrophin releasing hormone (GnRH). 4/5 - Anterior pituitary increases secretion of LH and FSH. Luteinising hormone (LH) stimulates secretion of testosterone (Leydig cells): - an enzyme in prostate gland and seminal vesicles converts testosterone into Dihydrotestosterone (DHT). Hormonal control of spermatogenesis II Follicle stimulating hormone (FSH) stimulates spermatogenesis: - with testosterone, stimulates sertoli cells to secrete androgen-binding protein (keeps hormone levels high). - testosterone stimulates final steps spermatogenesis. Control of testosterone production - Negative feedback system controls blood levels of testosterone - Receptors in hypothalamus detect increase in blood level - Secretion of GnRH slowed - Anterior pituitary (FSH & LH hormones) slowed - Leydig cells of testes slowed - Blood level returns normal Sperm production is high: - sertoli cells release inhibin. - inhibits FSH secretion by the anterior pituitary. - decreases sperm production Effect of inhibin hormone Sperm production is low: - less inhibin is released by the sertoli cells. - more FSH will be secreted. - sperm production will be increased. 5/5