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Ch 46 part 3: Human Reproduction- Fertilization, Pregnancy, & Birth

Ch 46 part 3: Human Reproduction- Fertilization, Pregnancy, & Birth. FERTILIZATION & IMPLANTATION. ● fertilization occurs in the oviduct ● female repro. tract produces secretions which capacitate sperm cells (final maturation)

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Ch 46 part 3: Human Reproduction- Fertilization, Pregnancy, & Birth

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  1. Ch 46 part 3: Human Reproduction- Fertilization, Pregnancy, & Birth

  2. FERTILIZATION & IMPLANTATION ● fertilization occurs in the oviduct ● female repro. tract produces secretions which capacitate sperm cells (final maturation) ● a capacitated sperm cell reaches the egg and must penetrate the ZONA PELLUCIDA *a glycoprotein membrane (protective jelly coat) surrounding the plasma membrane of an oocyte

  3. FERTILIZATION & IMPLANTATION ● when sperm cell binds to receptor molecules in Zonapellucida, the ACROSOME releases its contents (i.e. digestive enzymes) so that it can penetrate the plasma membrane of the egg (= “acrosomal reaction”)

  4. FERTILIZATION & IMPLANTATION ● sperm cell membrane fuses to egg membrane & the sperm nucleus enters ● binding of membranes triggers depolarization/ biochemical changes (called: cortical reaction) which blocks other sperm from entering (polyspermy) cortical granules release enzymes that destroy sperm binding proteins

  5. FERTILIZATION & IMPLANTATION ● cleavage (mitotic cell division) begins approx. 24 hours after conception ● after 3-4 days, embryo contains approx. 16 cells (MORULA) ● Unequal cell division after this cause a fluid filled cavity to form ● embryo reaches uterus approx. 7 days after fertilization & contains approx. 100 cells (BLASTOCYST)

  6. Morula

  7. FERTILIZATION & IMPLANTATION ● the embryo will embed (implant) into the endometrium within next 5 days ● for the first 2-4 weeks, embryo obtains nutrients directly from endometrium

  8. Recall that the pregnancy is maintained due to HCG secreted by the embryo/fetus • Gradually, the placenta develops and produces progesterone (at around 8 - 10 weeks), at which point the corpus luteum is no longer needed

  9. Placenta: Structure & Function • The placenta is a disc-shaped structure that nourishes the developing embryo • Formed from the development of the outer cells of the blastocyst (trophoblast) upon implantation; eventually invades the uterine wall

  10. The umbilical cord connects the fetus to the placenta and maternal blood pools via open ended arterioles into intervillous spaces (lacunae)

  11. Chorionic villi extend into these spaces and facilitate the exchange of materials between the maternal blood and fetal capillaries • Nutrients, oxygen and antibodies will be taken up by the fetus, while carbon dioxide and waste products will be removed

  12. Placenta: Hormonal Function • takes over the hormonal role of the ovary (at around 12 weeks) • Estrogen stimulates growth of the muscles of the uterus (myometrium) and the development of the mammary glands • Progesterone maintains the endometrium, as well as reduces uterine contractions and maternal immune response (no antibodies against fetus) • Both estrogen and progesterone levels drop near time of birth

  13. HUMAN GESTATION: 3 trimesters ● 1st trimester: organogenesis • At 8 weeks, embryo is called a fetus • 5 cm long by the end of trimester ● 2nd trimester: hormone levels stabilize & placenta takes over progesterone production • Uterus & fetus growing! • Can feel fetal movements ● 3rd trimester: as fetus grows, activity decreases • Mother’s abdominal organs become displaced • Complex interplay of local regulators (prostaglandins) & hormones (estrogen & oxytocin) induces labor

  14. BIRTH • Childbirth controlled by the hormone oxytocin; high estrogen levels during the last weeks of pregnancy trigger formation of oxytocin receptors in uterus • the fetus takes up all available space in the uterus (stretching the walls of the uterus) • This causes a signal to be sent to the brain, releasing oxytocin from the posterior pituitary

  15. Oxytocin: • inhibits progesterone (inhibiting uterine contractions) • directly stimulates the smooth muscle of the uterine wall to contract; initiates the birthing process • Uterine wall contractions cause further stretching, which triggers more oxytocin to be released (causing even more contraction) • Positive feedback! • The fetus responds to the cramped conditions by releasing prostaglandins which cause further uterine muscle contractions

  16. Contractions will stop when labor is complete and the baby is birthed (no more stretching of the uterine wall)

  17. birth bookmark!

  18. POST- BIRTH ● decreased levels of progesterone after birth remove inhibition from anterior pituitary which allows for prolactin secretion

  19. POST-BIRTH ● prolactin stimulates milk production after 2-3 days ● oxytocin controls release of milk from mammary glands

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