Pregnancy & Human Development

1. Pregnancy & Human Development Chapter 29

2. Fertilization: It’s all in the timing! • Oocyte is only viable for ~ 24 hours. • Sperm is viable for 12 – 24 hours (some “super sperm” may be viable for up to 72 so be careful!) • Therefore, usually, coitus must occur within a 24 hour window on either side of ovulation.

3. Barriers to fertilization • Low vaginal pH • Getting lost (50/50 chance of getting the right uterine tube) • Numerous defective sperm • Uterine contractions • Phagocytes • By the time they get to the oocyte, there are only a few dozen to a couple hundred

4. Capacitation • Must occur before spermatozoa can fertilize secondary oocyte: • contact with secretions of seminal vesicles • exposure to conditions in female reproductive tract

5. Penetration Secondaryoocyte Head of sperm 1650X

6. Fertilization Figure 29–1

7. Fertilization Figure 29–1b (1 of 2)

8. Fertilization Figure 29–1b (2 of 2)

9. Fusion Of the pronuclei

10. Cleavage and Blastocyst Formation Figure 29–2

11. What’s this thing called, Love? • Zygote – a the single cell after fusion of the pronuclei of the oocyte & the sperm. • Conceptus – covers the period of develop following first cleavage and differentiation of cells into an embryo. • Morula – the conceptus as a solid ball of 16 cells (about day 3). • Blastocyst – a hollow ball of cells, from day 4. “Hatching” occurs at this stage, when the blastocyst emerges from the zona pellucida.

12. Development from zygote to implantation.

13. Then what ? • The blastocyst differentiates into: • the trophoblast, the outer ball of cells that eventually becomes the placenta and “extraembryonic” membranes. • the inner cell mass (ICM) becomes the embryo. • The above occurs over the course of the second week following conception. • Implantation – occurs on about day 6 or so, as the blastocyst burrows into the endometrium.

14. Stages in Implantation Figure 29–3

15. Implantation Day 6

16. Implantation – Day 8

17. ImplantationDays 9 - 13and early placentation

18. Ectopic Pregnancy • Implantation occurs outside of uterus • Do not produce viable embryo • Can be life threatening

19. The Inner Cell Mass and Gastrulation Figure 29–4

20. The Primary Germ Layers ECTODERM MESODERM ENDODERM

21. The Fates of the Germ Layers Table 29–1

22. Extraembryonic Membranes and Placenta Formation Figure 29–5 (1 of 3)

23. Figure 29–5 (2 of 3)

24. Placenta Formation Figure 29–5 (3 of 3)

25. View of Placental Structure Figure 29–6a

26. Placental Structure Figure 29–6b

27. Decidua: Decidua Capsularis • Thin portion of endometrium • No longer participates in nutrient exchange and chorionic villi in region disappear Decidua Basalis • Disc-shaped area in deepest portion of endometrium • Where placental functions concentrated Decidua Parietalis • Rest of the uterine endometrium • No contact with chorion

28. Hormones of Placenta • Synthesized by syncytial trophoblast, released into maternal bloodstream: • human chorionic gonadotropin • human placental lactogen • placental prolactin • relaxin • progesterone • estrogens

29. Human Placental Lactogen (hPL) • Helps prepare mammary glands for milk production • Stimulatory effect on other tissues comparable to growth hormone (GH) Placental Prolactin • Helps convert mammary glands to active status

30. Relaxin • Is a peptide hormone • Is secreted by placenta and corpus luteum during pregnancy • Increases flexibility of pubic symphysis, permitting pelvis to expand during deliveryCauses dilation of cervix • Suppresses release of oxytocin by hypothalamus and delays labor contractions

31. An Overview of Prenatal Development Table 29–2 (1 of 4)

32. An Overview of Prenatal Development Table 29–2 (2 of 4)

33. An Overview of Prenatal Development Table 29–2 (3 of 4)

34. An Overview of Prenatal Development Table 29–2 (4 of 4)

35. Embryogenesis • Body of embryo begins to separate from embryonic disc • Body of embryo and internal organs start to form • Folding, differential growth of embryonic disc produce bulge that projects into amniotic cavity: • projections are head fold and tail fold

36. The First Trimester Figure 29–7a, b

37. The First Trimester Figure 29–7c, d

38. Organogenesis • Process of organ formation

39. The Second and Third Trimesters Figure 29–8

40. Second Trimester • Fetus grows faster than surrounding placenta

41. Third Trimester • Most of the organ systems become ready • Growth rate starts to slow • Largest weight gain • Fetus and enlarged uterus displace many of mother’s abdominal organs

42. Growth of the Uterus and Fetus Figure 29–9a, b

43. Growth of the Uterus and Fetus

44. Progesterone • Released by placenta • Has inhibitory effect on uterine smooth muscle • Prevents extensive, powerful contractions

45. Opposition to Progesterone • 3 major factors: • rising estrogen levels • rising oxytocin levels • prostaglandin production

46. Initiation of Labor and Delivery Figure 29–10

47. False Labor • Occasional spasms in uterine musculature • Contractions not regular or persistent True Labor • Results from biochemical and mechanical factors • Continues due to positive feedback

48. Hormone levels throughout pregnancy

49. Placental hormones

50. Contractions • Begin near top of uterus, sweep in wave toward cervix • Strong, occur at regular intervals, increase in force and frequency • Change position of fetus, move it toward cervical canal