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University of Toronto St. George
Michelle French

Pregnancy October-27-12 3:00 AM Where does fertilization occur? • Oocyte viable for 24h ,sperm for 4-6 h • Sperm deposited in vagina must mature and travel before fertilization o Sperm undergoes capacitation, becomes hyperactive o Albumin ,enzymes, lipoproteins bind to sperm: • Glycoprotein coat removed • Intracellular changes • Develop strong whip like motion o Sperm must pass through (~30 min) cervical mucous (thin, estrogen -> gets thinner with estrogen, thicker with progesterone) o Uterine and oviduct contractions aid transport • Estrogen, prostaglandins - semen) Fertilization • About 100 sperm reach the oocyte • Guided by chemotaxis (production form cumulus cells) • Sperm tunnel through barriers (acrosomal enzymes) • First sperm fusing with egg wins • Acrosomal reaction o Membrane in front breaks down and the contents of the acrosome are released • Sperm docks with sperm-binding proteins on oocyte membrane • Triggers depolarization of oocyte • Fusion of cortical granules (vesicles) with membrane • Contents coat oocyte and prevent penetration of other sperm (i.e. prevents polyspermy) -> can't have more than one sperm per egg because not viable • Oocyte partially in meiosis 2, activated when the sperm enters • Half the female genetic material is removed • You can see the different male and female nuclei for a bit, then they fuse After fertilization 1. Ovulation 1. Day 1: fertilization 1. Days 2-4 cell division takes place in fallopian tube (fallopian tube relaxed because of high progesterone 2. Days 4-5 blastocyst reaches uterus 3. Days 5-9 blastocyst implants (invades the uterine endometrium) • Blastocyst consists of trophoblast and inner cells (embryo and other structures) Implantation • Decidua produced from endometrial cells, secrete several hormones and growth factors • Surface of uterine lining closes in after the blastocyst has been implanted Prevention of menses • Human chorionic gonadotropin (hCG) secreted from trophoblast then placenta is the signal to prevent menses • Similar structure to LH • hCG first hormone to peak o LH in the ovary causes the cells to release estrogen and progesterone o hCG signals to continue to make estrogen and protesterone as is similar to LH • Progesterone and estrogen peak just before delivery whereas hCG peaks in first trimester and rapidly goes down • hCG is what is detected in pregnancy kits hCG maintains the corpus luteum • High progesterone levels keep the endometrium intact • Progesterone, inhibin, estrogen: feedback suppression of pituitary Fetus and placenta • Performs role of digestive, respiratory and renal systems for the fetus • Exchange of o Nutrients and waste o Oxygen and carbon dioxide o Proteins, chemicals etc. • Embryo attached to the placenta, also has vein and artery for blood supply Placental circulation • Maternal endometrial vessels will break down • the mother's blood and the fetal blood does not usually mix • Easy gas exchange between the maternal blood vessels and the umbilical vein Placenta is a temporary endocrine gland • 10% of the mother's blood coming out of the heart goes to the placenta • Placenta makes: o hCG o Progesterone o Estrogen o Human placenta lactogen & more • It has complete independence from the ovary • Once the placenta makes other hormones, production of hCG goes down and
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