Reproductive Physiology I_ Female Reproductive Cycle.pdf

12/01/24 Reproductive Physiology I: Female Reproductive Cycle Learning objective: describe the physiology of the ovaries and the hormonal control of oogenesis and ovulation. What is oogenesis: The formation and maturation of ova from undifferentiated cells in the ovary. Primordial follicles primary...

12/01/24 Reproductive Physiology I: Female Reproductive Cycle Learning objective: describe the physiology of the ovaries and the hormonal control of oogenesis and ovulation. What is oogenesis: The formation and maturation of ova from undifferentiated cells in the ovary. Primordial follicles primary follicles oocytes secondary oocyte Ovaries: Structure: Develops from Mesonephros and gonads ridge. Bilateral. Attached to the anterior abdominal wall by the suspensory ligament of the ovary and to the uterus by the ovarian ligament. Contains: stroma, oocytes, follicular and granulosa cells. Ovarian function vs testicular function: Relatively few oocytes released. Release is not in a continuous stream, occurs episodically at ovulation. Pre-ovulation: oestrogen dominance. Post-ovulation: progesterone dominance. Changes in the ovary throughout life: Fetal: 7 million oocytes develop in fetus. 2 million at birth left. Follicular development arrested a prophase of meiosis I. start of Menarche: them.gg struar Follicular maturation restarted. time a Perimenopause: when begins menopause Low levels of follicular recruitment. Less responsive to LH and FSH. Follicle stimulating hormone (FSH): Peptide hormone Gonadotrophin produced by Gonadotrophin cells of the anterior pituitary gland. Stimulated by GnRH. Act upon granulosa cells to produce oestrogen. Surge of circulating oestrogen from most advanced follicles. Stimulate LH receptors on the granulosa cells. Luteinising hormone (LH): Produced by Gonadotrophin cells of the anterior pituitary gland in response to GnRH. Acts upon theca interna cells of the ovary to produce androgen. LH receptors on the maturing ovarian follicle further promote oestrogen production. Before LH surge proceeds ovulation. Oogenesis: Early oocyte growth: Primordial to Primary Approx 20 per day. Restart meiosis I. Diploid cell ( 46 Chromosomes ) become haploid ( 23 chromosomes ). Extrudes rst polar body. Secondary follicle: Made up of: oocyte, zona pellucida, granulosa cells and theca cells. Starts meiosis II. Only completes meiosis II at fertilisation. Extrudes secondary polar body. Produced haploid secondary oocyte ( mature ovum ). Follicular development gets to a point when further development requires external support. If the right hormone levels are not there, the follicles will just undergo atresia. Secondary follicles produce steroids as they grow: Only theca interna cells bind LH. Theca cells synthesise androgens from acetate and cholesterol. FEEL Granulosa cells can’t form androgens, but they can convert androgens ( via Aromatase ) to oestrogens when stimulated by FSH. Ovulation: Expanding of the secondary follicles that will die without LH surge. LH surge occurs, 12–24 hours prior to ovulation. Final follicular development to pre-ovulatory stage. After ovulation, GC become granulosa lutein cells, which synthesise progesterone. GC lose their capacity to bind to oestrogen and FSH. Rapid change in size, bulge at ovarian surface. Connective tissue breaks down and follicle ruptures. Follicular uid is released and the oocyte and cumulus cells extruded. Post-ovulation stage: Ovum is captured by the mbria. Corpus luteum forms and produces progesterone to support implantation. Implantation – LH falls and hCG maintains pregnancy. Later production of hCG is from the syncytiotrophoblasts of the placenta. Corpus luteum: GC cells become hypertrophic and form large lutein cells. Increasing progesterone. If implanted, hCG from syncytiotrophoblasts replaces activity of the corpus luteum. If not implanted then becomes corpus albicans.