BIOL 252 1st Edition Lecture 26 Outline of Last Lecture I. Oogenesis and Sexual CycleII. OogenesisIII. FolliculogenesisIV. Sexual CycleV. Ovarian CycleVI. Menstrual CycleOutline of Current LectureI. Review of Sexual CycleII. Menstrual CycleIII. Pregnancy’s Effect on Sexual CycleIV. CapacitanceV. Oocyte at FertilizationVI. Events following fertilizationCurrent LectureI. Review of Sexual Cyclea. Follicular Phasei. Positive feedback responsible for FSH/LH spike preceding ovulationii. Maturing follicle secretes estradiol1. Follicles release estrogen iii. Estradiol stimulates hypothalamus and anterior pituitaryiv. Hypothalamus secretes GnRHv. Pituitary secretes LH and FSH vi. Oocyte completes meiosis I; follicle rapidly enlarges and then ovulates b. Luteal Phasei. 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 progesterone1. Uterus continues to developiii. Follicle cells undergo transition1. Corpus luteum => cell death, involution -> scar tissue, corpus albicansThese 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.iv. Hormones in high concentration have inhibitory effect1. Estrogens, inhibin, progesterone high levels => levels to declineII. Menstrual Cyclea. Day 1: first day of noticeable vaginal dischargei. Days 1-5 = menstrual phase w/ menstrual fluidii. Days 6-13 = proliferative phase b. Day 14: ovulationc. Day 15: fertilization i. Days 15-26 = secretory phased. Day 24: implantation e. Days 26-29: premenstrual phase f. Poll Everywherei. Birth control pills contain progesterone. What property of explains its contraceptive nature?1. Prevents formation of corpus luteuma. Not true – corpus luteum formed as direct result of ovulation 2. Prevents menstrual phase of uterine cyclea. Yes it does; but don’t need menstrual to conceive3. Maintains secretory phase of uterine cyclea. Yes it does; but you want this for implantation 4. Inhibits GnRHa. Yes it does!III. Pregnancy’s Effect on Sexual Cyclea. hCG  corpus luteum  progesterone i. hCG produced by embryoii. Sustains corpus luteum (stands in for LH)IV. Capacitancea. Although sperm may arrive at egg in as little as 30 minutes, not ready for fertilizationb. Sperm acquire capacity for fertilization while in female reproductive tract and willbe viable up for up to 3 daysc. Egg has short window of fertilizationi. Ovulated oocyte viable for up to 24 hoursd. Fertilization has to take place w/in 24 hourse. Window for intercourse that would results in fertilization: up to three days beforeand one day after ovulation = 4 DAYSV. Oocyte at Fertilizationa. Oocyte is surrounded by zona pellucida and corona radiate (cumulus)b. Acrosome reaction: acrosome membrane breaks down spilling its enzymes; digesting path to egg membranei. Bursting apart of membranes; enzymes spilled outii. Takes many sperm to digest a pathc. Fusion of egg and sperm membranei. First part of fertilizationd. Cortical reactioni. 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 space3. Cut up zona pellucida, letting water seep through 4. Membrane swells, pushes other sperm away and hardens (makingit hard for sperm to get through) e. Fertilization membrane – rejected sperm VI. Events following fertilizationa. Arrest at Meiosis II lifted; meiosis II completesb. 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 trophoblasti. Stimulates corpus luteum to secrete progesteroneii. Trophoblast development into chorion that takes over role of corpus luteum c. Embryogenesisi. ICM forms 3 structures1. Trilaminar embryoblast2. 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 circulationi. Embryonic blood is surrounded by maternal sinusoidsii. Embryonic and maternal blood does not mix; but does have exchange (wastes, gases,