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Unformatted text preview: PSL302: Lecture 34, by Prof. French! Monday, Dec. 6, 2010 Pregnancy
Outline 1. Where does fertilization occur? 2. What happens after fertilization? 3. What prevents menses? 4. What endocrine gland is temporary? 5. How is labour triggered? 6. What hormones are necessary for breast milk? 7. How can reproduction stimulate neurogenesis? Suggested textbook reading: 855-861 (5th ed) 848-854 (4th ed) 1. Where does fertilization occur? - Sperm deposited into vaginal tract = must swim thru uterus into Fallopian tubes -> female reproductive tract has contractions that propel swimming sperm up to tubes - 1 ejaculate: 180mil sperm - BUT only 1,000 make it up to tubes - Egg is fertilized close to ovaries in tubes - Zygote travels to uterus and implants = division & diffation - Cervical mucous: barrier against sperm - Before ovulation: [estrogen] [progesterone] = mucous thinner ! ! = sperm can easily pass through - After ovulation: [estrogen] [progesterone] = mucous thicker ! ! = in case egg is fertilized, protects egg from microorganisms - Viability of gametes: - Oocyte viable for 24h before it degenerates! - Spermatozoa viable 4-6 days Sperm deposited in vagina must mature & travel before fertilization - Recall: sperm anatomy - Acrosome is a vesicle containing enzymes - Head contains DNA - Sperm undergoes capacitation = becomes hyperactive - Initiated by binding of albumin, enzymes, lipoproteins (in f-tract) - Glycoprotein coat removed - Intracellular changes = tail develops strong whip-like motion - Sperm must pass thru (~30 min) cervical mucous - Mucous thinner when [estrogen] (before ovulation) - Uterine & oviduct contractions aid transport to oocyte - Initiated by estrogen & prostaglandins in semen Where does fertilization occur? Oocyte viabl 24h Spermatozo viable 4-6 da Figure 26.18, step 2 g , p Sperm deposited in vagina m travel before fertiliz
head mid piece acrosome Sperm undergoe hyperactive Albumin, enzyme sperm: glyocopro intracellul develop s tail (flagellum) Sperm must pass cervical mucous Uterine & oviduct transport (estrogen, prot Figure 26.10 1 of 8 PSL302: Lecture 34, by Prof. French! Monday, Dec. 6, 2010 Fertilizaton Fertilization About 100 sper Fertilizaton - Sperm guided by chemotaxis (attracted to progesterone) Guided by chem - Receptors similar to odorant receptors that bind (progesterone f About 100 sperm reach oocyte progesterone Sperm tunnel th Guided by chemotaxis - ~100 sperm reach oocyte (acrosomal e (progesterone from cumulus cells) - Sperm must penetrate into oocyte First sperm fus Sperm tunnel through barriers - Oocyte suspended in meiosis II (metaphase stage) (acrosomal enzymes) - Follicular cells surrounding oocyte (ovulated w/ oocyte) First sperm fusing with egg wins - Called cumulus cells: secrete progesterone Acrosomal reaction - Form corona radiata - Final barrier: zona pellucida Acrosomal reaction - Sperm tunnel thru barriers - Undergo acrosomal rxn Figure modified from: http://www.embryology.ch/anglais/dbefruc - Acrosome breaks open & releases acrosomal enzymes Figure modified from: http://www.embryology.ch/anglais/dbefruchtung/akrosom02.html - Enzymes break down zona pellucida - First sperm fusing w/ egg wins! - Rxn prevents other sperm from fusing w/ oocyte Fertilizaton continued - Sperm docks w/ sperm-binding proteins (species-specific) on oocyte membrane Figure 26.17 - Sperm & oocyte membranes fuse Sperm docks with sperm-binding proteins on oocyte membrane - Triggers depolarization of oocyte = membrane potential - In oocyte: fusion of vesicles w/ cortical granules -> membrane Triggers depolarization of oocyte - Contents coat oocyte Fusion of cortical granules (vesicles) with membrane - Prevent penetration of other sperm Contents coat oocyte and prevent penetration of other sperm - I.e. prevents polyspermy (too many gametes added) - Triggers completion of meiosis II in oocyte (i.e. prevents polyspermy) - Initial formation of female & male nuclei - Nuclei fuse -> 2nd meiotic division = zygote nucleus + 2nd polar body formed 2. What happens after fertilization? - Days 2-4: in Fallopian tubes - Zygote undergoes mitosis -> 2-cell & 4-cell stages = borula - Days 4-5: eventually, borula -> blastocyst - Blastocyst: hollow sphere w/ inner cell mass & outer cell structure (trophoblast) 2 of 8 PSL302: Lecture 34, by Prof. French! Monday, Dec. 6, 2010 - Requires at least 4 days for transport - Oviduct still constricted: prevents oocyte from moving too far, too fast - During luteal phase: begins to open up w/ [progesterone] - Allows endometrium to prepare for implantation as [progesterone] - Days 5-9: in uterus - Blastocyst floats around before implantation in endometrium - Blastocyst structure: What to fetal contribution to placenta - Trophoblast: gives risehappens after fertilization? - Inner cells: give rise to embryo itself
(embryo + other structures) trophoblast Implantation Implantation
Figure 26.18 syncitium - Implantation: zygote is set up for formation of placenta & embryo devlpt Decidua Blastocyst not endometrial cells, secrete several - Image 1: produced fromfully submerged under endometrium hormones and growth factorscytotrophoblasts (buried) - Inner cell mass close to - Lots of commc btwn uterine cells & trophoblast cells - Endometrial cells become decidua - Secrete hormones + growth factors to devlp trophoblasts -> syncitium - Image 2: Full implantation of blastocyst - Trophoblast gives rise to chorion -> placenta - If no fertilization occurs, corpus luteum degenerates -> [estrogen & progesterone] - Endometrium shed = menses - If fertilization has occurred, want endometrium maintained - The chorion (of embryo) must release hormone -> act on ovary to keep corpus luteum - Keep [progesterone & estrogen] = maintain endometrium
3 of 8 Human chorionic gonadotropin (hCG) secreted from trop /placenta
PSL302: Lecture 34, by Prof. French! Similar in structure to LH Monday, Dec. 6, 2010 3. What prevents menses? - Human chorionic gonadotropin (hCG) secreted from trophoblast/placenta (chorion) - Similar in structure to LH (similar fxn) - Recall: LH acts on corpus luteum - Diagram: fertilization occurs in middle of cycle - Rapid [hCG] required shortly after fertilization - Maintains corpus luteum (continues to secrete progesterone & estrogen) - Then rapidly by 1st trimester (3rd month of pregnancy), then to zero at delivery - [Estrogen & progesterone] steadily throughout pregnancy - Initially produced by corpus luteum - Later produced by placenta - Rapidly at delivery In ovary: hCG maintains the corpus luteum - Progesterone & estrogen maintain endometrium (for embryo devlpt) - Also -ve feedback to inhibin -> suppress pituitary release of LH & FSH, & GnRH - No further ovulation - Fraternal twins: two oocytes ovulated at same time & fertilized at same time - Identical twins: zygote splits early on = two identical blastocytes - Pregnancy tests detect hCG metabolites in urine Embryonic/placental devlpt (FYI)
hCG maintains the corpus luteum
Ovary hCG corpus luteum Embryonic/placental development (FYI) Progesterone keeps endometrium intact Progesterone, estrogen, inhibin: feedback suppression of pituitary Figure from: http://www.columbia.edu/itc/hs/medical/sbpm_histology/lab/lab19_ovary.html Week 2 Week W k4 - Week 2: embyro forms more structures: - Yolk sacs (present in embryonic life) - Amnion (where amniotic fluid will be found)Figures from Martini (2006) Fundamentals of Anatomy and Physiology y y gy - Week 4: embryo has devlping head & tail - Embryonic head & tail folds; also embryonic gut, close to yolk sac - Yolk sac enlarges & devlps yolk stalk
4 of 8 PSL302: Lecture 34, by Prof. French! Monday, Dec. 6, 2010 Much later: Fetus and placenta - Fetus now pushed out from uterine lining - Amnion around fetus - Fetus floats in amniotic fluid - Blood vessels coming to and from fetus to placenta (rooted in uterus) - Placenta performs role of digestive, respiratory & renal systems for fetus - Exchange of nutrients/waste, O2 & CO2, proteins, chemicals, etc. - During birth: - Amniotic membrane breaks = initiate labour - Baby exits first, then placenta expelled from uterus ("afterbirth") - Umbilical cord is cut Placental circulation - Right: uterus -> maternal blood vessels - Left: fetal blood vessels -> capillaries clustered in chorionic villi - Fine membrane separates maternal & fetal blood (no mixing) but allows exchange - Maternal O2ed blood pools in sinus cavities - Bathes chorionic villi: exchange contents w/ fetal blood - Drains into maternal venous system - Umbilical arteries (blue): carry deO2ed blood from embryo to placenta - Umbilical veins (red): carry O2ed blood back to embryo Fetus and placenta Placent Perform Digestiv Di ti renal sy Exchang E h nutrien oxyge protein Placental circulation
Figure 26.19 g 4. What endocrine gland is temporary? Placenta What ovary - Complete independence from endocrine gland is temporary? - Chorion (early placenta) secretes Placenta hCG = maintain corpus luteum - Placenta now secretes progesterone & estrogen (peak before delivery) - Also secretes human placental lactogen (also human chorionic somatomammotropin)
Human chorionic gonadotropin Progesterone Estrogen st oge Human placental lactogen (also called human chorionic somatomammotropin) days of pregnancy Figure 26.19 5 of 8 PSL302: Lecture 34, by Prof. French! Monday, Dec. 6, 2010 By placenta: Secretion of estrogen & progesterone - Cooperation in pdc of hormones btwn mother, fetus and placenta - Placenta doesn't immediately secrete estrogen - B/c fetus has a role in secretion of estrogen Secretion of estrogen and progesterone - Recall: Estrogen & progesterone are steroid hormones - Derived from cholesterol -> converted into other hormones th placenta by b the l t - Early on, converted into progesterone - Top line: Cholesterol easily passes btwn Mother's Placenta mother & fetus Blood - Middle line: Placental synthesis of cholesterol cholesterol progesterone progesterone rogesterone progesterone rogesterone - Takes maternal cholesterol -> DHEA converts it to progesterone - Secreted into maternal blood estrogen estrogen - Bottom line: Placenta synthesis of estrogen: - Maternal cholesterol -> enters fetal DHEA = dehydroepiandrosterone blood -> travels to fetal adrenal cortex -> converts it into DHEA (dehydroepiandrostrone) - Diffuses back to placenta -> converts it into estrogen
cholesterol Fetal Adrenal Cortex
cholesterol DHEA DHEA ~ Sherwood and Kell (2010) Human Physiology from Cells to Systems - Conversion of estrogen takes time - Must wait for fetal adrenal cortex to develop before placenta can take over in secreting estrogen - This is why corpus luteum must secrete estrogen for a while - Placental estrogen called estriol Function of placental hormones - Human chorionic gonadotropin - Maintains corpus luteum (ensures [estrogen & progesterone] early on) - Stimulates fetal testis in males (Leydig cells: release testosterone) - Progesterone - Suppresses uterine contractions (not until end of pregnancy) - Maintains cervical plug (mucous remains thick - Mammary gland devlpt (will secrete milk after birth) - Estrogen - Uterine devlpt (20-fold growth) - blood supply, oxytocin receptors (cause contractions, inhibited) - Breast duct devlpt, etc. - Human placental lactogen - Structurally related to growth hormone & prolactin - in mother & in fetus - maternal cellular uptake of glucose (allow more glucose available for fetus) - May cause gestational diabetes in mothers - Enhances maternal lipolysis - So mother has energy source other than glucose 6 of 8 PSL302: Lecture 34, by Prof. French! Monday, Dec. 6, 2010 5. How is labour triggered? - Before parturition: relaxin released from ovary + placenta - Loosens ligaments in pelvic bone - Cause cervix to loosen - Triggers/Initiation: - estrogen cause oxytocin receptors in uterus - gap jxns btwn smooth muscle cells in uterus - sensitivity of oxytocin receptors How is labour triggered? - Overall, sensitivity of uterus to estrogen - fetal cortisol Before parturition, relaxin released from ovary and placenta - Fetus under stress during late pregnancy loosens the ligaments (CRH) - placental corticotropin-releasing hormone in the pelvic bone and cause the cervix - fetal cortisol - prostaglandins (released from uterine walls) - progesterone Triggers/Initiation? - In some animals: inhibition of uterine Estrogen & oxytocin receptors in contractions removed uterus increase - Once labour initiated: weak contractions Fetal cortisol - Fetus drops lower in uterus = cervical stretch Placental corticotropin-releasing - Cervical stretch triggers oxytocin release from post. hormone (CRH) pituitary = +ve feedback Prostaglandins - Cause uterine contractions Progesterone (some animals) - Prostaglandins released from uterine walls -> cause more uterine contractions What hormones are necessary for brea - +ve feedback stops after baby is delivered
Figure Before parturition 26.21 6. What hormones are necessary for breast milk? - Before parturition: estrogen & progesterone - Needed for devlpt of mammary glands - Milk ducts are surrounded by smooth muscle (myoepithelial cells) - BUT inhibit milk pdc until after birth - After parturition: prolactin & oxytocin - Prolactin: stimulates epithelial milk-producing cells After parturition ! ! = milk pdc - Oxytocin: stimulates myoepithelial cells to contract ! ! = push milk out from nipple (milk letdown) What hormones are necessary for breast m Estrogens an progesterone the developm mammary gla inhibit milk pr Prolactin - Prolactin & oxytocin both made in pituitary gland
- But in diff parts of gland - Secretion regulated somewhat differently Figure 26.22 Oxytocin Epithelial milkproducing cells Myoepithel Prolactin and oxytocin are both released from the pituitar How is the release regulated? 7 of 8 Fi PSL302: Lecture 34, by Prof. French! Monday, Dec. 6, 2010 Regulation - Middle of diagram: [prolactin & oxytocin] in pituitary - Oxytocin released from neurons in p. Pituitary - Cell bodies in hypothalamus & project to p. Pit. - Travel to blood = smooth muscle contraction - Prolactin released from neurons in a. Pituitary - Before birth: secretion inhibited by dopamine (PIH) - Dopamine secreted in hypothalamus -> travel thru hypophysial portal - Males also secrete prolactin but inhibited - After birth: sensory stimulation -> dopamine inhibition removed - Prolaction & released = milk pdc & ejection - As baby suckles more & when baby's cry is heard, more milk produced + ejected - So some women have to wear breast pads Regulation PIH = dopam 8 of 8 ...
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This note was uploaded on 03/27/2012 for the course PSL PSL300 taught by Professor Mackayfrench during the Fall '11 term at University of Toronto- Toronto.
- Fall '11