Overview of Reproductive System - Physiology and Anatomy - Lecture Slides, Slides of Physiology

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Overview of Reproductive System • Primary sex organs (gonads) – Produce gametes (testes or ovaries) - – Gametogenesis - spermatogenesis or oogenesis • Secondary sex organs – Male - ducts, glands, penis deliver sperm cells – Female - uterine tubes, uterus and vagina receive sperm and nourish developing fetus • Secondary sex characteristics – Develop at puberty to attract a mate • pubic, axillary and facial hair, scent glands, body morphology and low-pitched voice in males Docsity.com Spermatogenesis • Spermatogonia produce 2 kinds of daughter cells – Type A remain outside blood- testis barrier and produce more daughter cells until death – Type B differentiate into primary spermatocytes • Cells must pass through BTB to move inward toward lumen - new tight junctions form behind these cells • meiosis I → 2 secondary spermatocytes • meiosis II → 4 spermatids Docsity.com Testosterone • Most from interstitial cells of testes with small amounts from adrenal glands and sustentacular cells • Causes enlargement and differentiation of male genitals and reproductive duct system • Necessary for sperm cell formation • Required for descent of testes • Hair growth on certain parts of the body • Skin is rougher and coarser • Quantity of melanin increases • Increases rate of secretion of sebaceous glands • Hypertrophy of larynx • Increases metabolic rate • Increases red blood cell count • Increases protein synthesis, rapid bone growth • Causes closure of epiphyseal plates Docsity.com Mechanism and Effects of Testosterone Activity • Testosterone is synthesized from cholesterol • It must be transformed to exert its effects on some target cells – Prostate – it is converted into dihydrotestosterone (DHT) before it can bind within the nucleus • Requires the enzyme 5alpha-reductase – Neurons – it is converted into estrogen to bring about stimulatory effects • Reqires the enzyme aromatase • Testosterone targets all accessory organs and its deficiency causes these organs to atrophy Docsity.com Accessory Glands • Seminal vesicles – Empty into ejaculatory duct – Produce about 60% of semen – Secretion contains fibrinogen – High pH • Prostate gland – Produces about 30% of semen – Thin, milky secretion, high pH – Contain clotting factors, and fibrinolysin • Bulbourethral glands – Contribute about 5% to semen – Mucous secretion. Just before ejaculation – Helps neutralize pH of female vagina Docsity.com Emission and Ejaculation • Emission: accumulation of sperm cells and secretions of the prostate gland and seminal vesicles in the urethra • Controlled by sympathetic centers in spinal cord – Peristaltic contractions of reproductive ducts – Seminal vesicles and prostate release secretions • Accumulation in prostatic urethra sends sensory information through pudendal nerve to spinal cord • Sympathetic and somatic motor output – Sympathetic: constriction of internal sphincter of urinary bladder so semen and urine do not mix – Somatic motor: to skeletal muscles, urogenital diaphragm and base of penis causing rhythmic contractions that force semen out of urethra: ejaculation Docsity.com Female Reproductive Physiology Docsity.com Establishing the Ovarian Cycle • During childhood, ovaries grow and secrete small amounts of estrogens that inhibit the hypothalamic release of GnRH • As puberty nears, GnRH is released; FSH and LH are released by the pituitary, which act on the ovaries • These events continue until an adult cyclic pattern is achieved and menarche occurs Docsity.com Hormonal Interactions During the Ovarian Cycle • Day 1 – GnRH stimulates the release of FSH and LH • FSH and LH stimulate follicle growth and maturation, and low-level estrogen release • Rising estrogen levels: – Inhibit the release of FSH and LH – Prod the pituitary to synthesize and accumulate these gonadotropins • Estrogen levels increase and high estrogen levels have a positive feedback effect on the pituitary, causing a sudden surge of LH Docsity.com Hormonal Interactions During the Ovarian Cycle • The LH spike stimulates the primary oocyte to complete meiosis I, and the secondary oocyte continues on to metaphase II • Day 14 – LH triggers ovulation • LH transforms the ruptured follicle into a corpus luteum, which produces inhibin, progesterone, and estrogen Docsity.com Hormonal Interactions During the Ovarian Cycle • These hormones shut off FSH and LH release and declining LH ends luteal activity • Days 26-28 – decline of the ovarian hormones – Ends the blockade of FSH and LH – The cycle starts anew Docsity.com Ovarian Cycle - Follicular Phase • Menstruation (day 1) to ovulation(14) (variable) • Difficult to predict date of ovulation • Contains menstrual and preovulatory phases Docsity.com Ovarian Cycle - Preantral Phase • Discharge of menstrual fluid (days 1-5) • Before follicle develops antrum – primordial and primary follicles Docsity.com Ovarian Cycle - Antral Phase • Day 6 to 14, one dominant follicle advances to mature (graafian) follicle; secretes estrogen Docsity.com Uterine (Menstrual) Cycle • Series of cyclic changes that the uterine endometrium goes through each month in response to ovarian hormones in the blood • Days 1-5: Menstrual phase – uterus sheds all but the deepest part of the endometrium • Days 6-14: Proliferative (preovulatory) phase – endometrium rebuilds itself • Days 15-28: Secretory (postovulatory) phase – endometrium prepares for implantation of the embryo Docsity.com Menses • If fertilization does not occur, progesterone levels fall, depriving the endometrium of hormonal support • Spiral arteries kink and go into spasms and endometrial cells begin to die • The functional layer begins to digest itself • Spiral arteries constrict one final time then suddenly relax and open wide • The rush of blood fragments weakened capillary beds and the functional layer sloughs Docsity.com Extrauterine Effects of Estrogens and Progesterone • Estrogen levels rise during puberty • Promote oogenesis and follicle growth in the ovary • Exert anabolic effects on the female reproductive tract – Uterine tubes, uterus, and vagina grow larger and become functional – Uterine tubes and uterus exhibit enhanced motility – Vaginal mucosa thickens and external genitalia mature Docsity.com Accomplishing Fertilization • The oocyte is viable for 12 to 24 hours • Sperm is viable 24 to 72 hours • For fertilization to occur, coitus must occur no more than: – Three days before ovulation – 24 hours after ovulation • Fertilization – when a sperm fuses with an egg to form a zygote Docsity.com Sperm Transport and Capacitation • Fates of ejaculated sperm – Leak out of the vagina immediately after deposition – Destroyed by the acidic vaginal environment – Fail to make it through the cervix – Dispersed in the uterine cavity or destroyed by phagocytic leukocytes – Reach the uterine tubes • Sperm must undergo capacitation before they can penetrate the oocyte Docsity.com Acrosomal Reaction and Sperm Penetration • An ovulated oocyte is encapsulated by: – The corona radiata and zona pellucida – Extracellular matrix • Sperm binds to the zona pellucida and undergoes the acrosomal reaction – Enzymes are released near the oocyte – Hundreds of acrosomes release their enzymes to digest the zona pellucida Docsity.com