BIOL 252 1st Edition Lecture 26 Outline of Last Lecture I Oogenesis and Sexual Cycle II Oogenesis III Folliculogenesis IV Sexual Cycle V Ovarian Cycle VI Menstrual Cycle Outline of Current Lecture I Review of Sexual Cycle II Menstrual Cycle III Pregnancy s Effect on Sexual Cycle IV Capacitance V Oocyte at Fertilization VI Events following fertilization Current Lecture I Review of Sexual Cycle a Follicular Phase i Positive feedback responsible for FSH LH spike preceding ovulation ii Maturing follicle secretes estradiol 1 Follicles release estrogen iii Estradiol stimulates hypothalamus and anterior pituitary iv Hypothalamus secretes GnRH v Pituitary secretes LH and FSH vi Oocyte completes meiosis I follicle rapidly enlarges and then ovulates b Luteal Phase i High levels of LH stimulate granulosa and theca cells to form corpus luteum tissue structure w in ovary 1 LH transforms cells in ovary to become corpus luteum ii Corpus luteum produces progesterone 1 Uterus continues to develop iii Follicle cells undergo transition 1 Corpus luteum cell death involution scar tissue corpus albicans These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute II III IV V iv Hormones in high concentration have inhibitory effect 1 Estrogens inhibin progesterone high levels levels to decline Menstrual Cycle a Day 1 first day of noticeable vaginal discharge i Days 1 5 menstrual phase w menstrual fluid ii Days 6 13 proliferative phase b Day 14 ovulation c Day 15 fertilization i Days 15 26 secretory phase d Day 24 implantation e Days 26 29 premenstrual phase f Poll Everywhere i Birth control pills contain progesterone What property of explains its contraceptive nature 1 Prevents formation of corpus luteum a Not true corpus luteum formed as direct result of ovulation 2 Prevents menstrual phase of uterine cycle a Yes it does but don t need menstrual to conceive 3 Maintains secretory phase of uterine cycle a Yes it does but you want this for implantation 4 Inhibits GnRH a Yes it does Pregnancy s Effect on Sexual Cycle a hCG corpus luteum progesterone i hCG produced by embryo ii Sustains corpus luteum stands in for LH Capacitance a Although sperm may arrive at egg in as little as 30 minutes not ready for fertilization b Sperm acquire capacity for fertilization while in female reproductive tract and will be viable up for up to 3 days c Egg has short window of fertilization i Ovulated oocyte viable for up to 24 hours d Fertilization has to take place w in 24 hours e Window for intercourse that would results in fertilization up to three days before and one day after ovulation 4 DAYS Oocyte at Fertilization a Oocyte is surrounded by zona pellucida and corona radiate cumulus b Acrosome reaction acrosome membrane breaks down spilling its enzymes digesting path to egg membrane i Bursting apart of membranes enzymes spilled out ii Takes many sperm to digest a path VI c Fusion of egg and sperm membrane i First part of fertilization d Cortical reaction i Sperm nucleus fertilizes egg ii Sodium and calcium come rushing into cell iii Trigger depolarization of channels spreads iv Cortical granules vesicles as result of calcium that comes in fuse and release their contents 1 Fills space cortical reaction 2 Result enzymes in cortical granules enter extracellular space 3 Cut up zona pellucida letting water seep through 4 Membrane swells pushes other sperm away and hardens making it hard for sperm to get through e Fertilization membrane rejected sperm Events following fertilization a Arrest at Meiosis II lifted meiosis II completes b Blastomeres form morula then a blastocyst i Blastocyst phase w two identifiable cell populations 1 Group on outside trophoblast form epithelial sphere 2 Group on inside inner cell mass embryoblast forms mostly embryo 3 Syncytiotrophoblast cells undergoing mitosis very rapidly group of invading cells important for penetration of organization into uterine lining and source for hormone HCG a HCG secreted by trophoblast i Stimulates corpus luteum to secrete progesterone ii Trophoblast development into chorion that takes over role of corpus luteum c Embryogenesis i ICM forms 3 structures 1 Trilaminar embryoblast 2 Amnion bag of fluid important for protection 3 Yolk sac germ cells make spermatogonia or oogonia a Blood cells come from yolk sac d Once blood vessels close enough for capillary exchange placental nutrition completely replaces decidual nutrition by 2nd trimester e Placental circulation i Embryonic blood is surrounded by maternal sinusoids ii Embryonic and maternal blood does not mix but does have exchange wastes gases etc