Reproductive System.docx

[Reproductive System] Gonad + Germ cells: Gonad = organ where gametes are produced (e.g. testis and ovaries) also control sexual characteristics via hormones. Germ cells = cells which become gametes often indicated by cells before meiosis (e.g. spermatogonia + oogonia) [Primordial germ cell (PGC...

[Reproductive System] Gonad + Germ cells: Gonad = organ where gametes are produced (e.g. testis and ovaries) also control sexual characteristics via hormones. Germ cells = cells which become gametes often indicated by cells before meiosis (e.g. spermatogonia + oogonia) [Primordial germ cell (PGCs)] "Origin of sperm cells" PGCs arise from posterior yolk sax and arise until gonads are formed Gonads arise from genital ridge become testis or ovaries PGCs migrate into gonad and reside as germ cells [Spermatogenesis ] 1. Primordial germ cell (PGC) -- 3 to 6 weeks of embryogenesis PGCs are formed, 2 to 3 months of embryogenesis in human PGCs migrate to gonads (future testis) then become dormant 2. At Puberty Spermatogonia occurs which is when seminiferous tubules in testis mature, allowing spermatogonia to further proliferate and enter meiosis 3. Diploid spermatogonia proliferate by miotic cell division inside testis \*These first stages are Mitosis and called Spermatogonium 4. The Spermatogonia enters Meisosi-1 becomes Secondary Spermatocyte from Primary Spermatocyte (some enter meiosis but not all others function as 'stem cells' and proliferate) 5. Meiosis-2 takes place where Secondary Spermatocytes become Spermatids 6. Spermatids finally differentiate into Spermatozoa (Sperm) a. Nucleus condenses b. Formation of acrosome (head), secretory vesicle contains enzymes to penetrate oocyte c. Formation of Flagellum d. Mitochondria gathered at the midpiece, for movement of cilia (flagellum) e. Removal of excess cytoplasm \*Testis are made from seminiferous tubules. [Sertoli Cells] - Span from basement membrane to the lumen, thus surrounding differentiating spermatogonia - Produce enzymes and growth factors required for spermatogenesis - Also function as phagocyte to clean up residual cytoplasm of sperm \*Spermatogenesis take place in close relation to Sertoli cells [Leydig Cells (interstitial cells)] - Reside outside seminiferous tubules - Secrete testosterone in response to LH (Luteinising Hormone) - Sperms are released to the lumen and transferred to epididymis - The process of a release from Sertoli cells is call spermiation - Sperms are not motile yet when released [Epididymis ] - Reservoir of sperm with passage taking 1-21 days - Concentrates fluid by 100x - Long single duct with peristaltic contraction - Sperm undergoes further maturation acquiring mobility, increasing dependence on fructose for energy production [FEMALES] [Oogenesis:] 1. Primordial germ cell (PGC) -- 3 to 6 weeks of embryogenesis PGCs are formed, 6 to 12 weeks of embryogenesis in human PGCs migrate to gonads (future ovaries) Now become Oogonia 2. Oogonia now proliferate via mitotic cell division inside ovaries 3. After 12 weeks of embryogenesis Oogonium enters Meiosis-1's prophase and becomes primary oocyte 4. Follicular cells in ovary surround the oocyte, forming the primordial follicle a. 5 months of embryogenesis = 7 millions of primordial follicles b. At birth reduced to 0.7-2 million after degradation c. At puberty -- 700,000 of primordial follicles d. After puberty, a few primordial follicles re-commence meiosis every day, only one is ovulated per month 5. When puberty occurs maturation of oocyte and completion of Meiosis-1 happens, where Secondary Oocyte is formed, and first polar body is let out 6. Meisois-2 occur letting out second polar body and forming mature egg  [Maturation of follicles:] 1. Primordial follicle, with flat follicular cells 2. Primary follicle, with multi-layer follicular cells 3. Secondary follicle with antrum 4. Secondary follicle with antrum and "Graafian follicle" [Menstrual cycle ] Pituitary hormones -- LH reaches peak during ovulation, in preparation for fertilisation. Steady levels of FSH throughout, slight increase during maturing follicle stage but also peaks further during ovulation. Both decrease when preparing for implantation. Ovarian hormones- Progestogen increase gradually when secretory phase is occurring. Oestrogen fluctuates increasing at the end of proliferation phase decreasing till day 14, then increasing slightly during secretory phase finally decreasing till end of menstrual cycle. \*Ovulation occurs on day 14 The uterus consists of: 2 uterine tubes that lead to the body with a back wall called the fundus. The inner wall of the uterus is called endometrium with the cervix being the entrance to the body. [Ovulation] Ovum is collected by trumpet shaped distal end of the uterine tube (infundibulum) with fimbriae (finger like projections) [Fertilisation] - Can occur at the ampulla (the curve at the uterine tube) - Out of 300x10^6^ sperm only 200 reach oocytes - Sperm must migrate through follicular cells (corona radiata), zona pellucida using enzyme kin acrosome and finally fuse with membrane of oocyte \*Outer layer of the egg is called corona radiata, then the layer beneath that is zona pellucida, then there is the perivitelline space and finally the plasma membrane of the oocyte. - The fertilised egg travels to the uterus a. by day 4 it is 8 cells and at the end of uterine tube b. Day 5 early blastocyst forms i. Days 5-7 blastocyst forms inner cell mass (embryoblast) and trophoblast (extra embryonic tissues) c. Day 6-7 hatching occurs where blastocyst comes out of zona pellucida d. Day 8-9 implantation occurs [Implantation] 1. Blastocyst attaches to the endometrium at the embryonic pole 2. Some trophoblast cells (syncytiotrophoblast) invade into the endometrium, placenta formation starts 3. Inner cell mass becomes flat sheet of epiblasts and hypoblasts - Additional cavity appears on epiblast side (amniotic cavity) 4. Day 9-10 Full embedding occurs 5. Maternal blood enters cavities in trophoblastic layer. 6. Human chronic gonadotrophin (hcG) produced by syncytiotrophoblast, enter maternal blood 7. hcG maintains hormonal activity of corpus luteum to secrete oestrogen and progestogen [After Ovulation ] - Corpus luteum releases oestrogen and progestogen - Makes endometrium sectary phase, prepares for implantation - If no implantation, corpus luteum becomes degenerate after 14 days and becomes 'scar-like' structure called corpus albicans Contraception -- Oestrogen and progestogen pill which mimic secretory phase (initial phase)