1. Pregnancy & Human Development Ex. 44

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. Penetration Secondary oocyte Head of sperm 1650X

5. No Polyspermy!

6. Fertilization & First cleavage

7. 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.

8. Development from zygote to implantation.

9. 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.

10. Implantation – Day 6

11. Implantation – Day 7

12. Hormone levels in early pregnancy

13. Placental hormones

14. Implantation

15. Placentation

16. Fetus & placenta: 13 weeks

17. Embryonic Development Differentiation of the three primary germ layers

18. Germ layer formation, Part II

19. Neurulation: Part I

20. Neurulation: Part II

21. Gastrulation Formation of the primitive gut

22. Gasturlation part II

23. Organogenisis in a 5 week embryo

24. Differentiation of Mesoderm

25. Differentiation of Mesoderm continued

26. The Primary Germ Layers All nervous tissueMuscleG.I. epithelium Epidermis & Derivatives Connective tissueDigestive glands Cornea & lensLymphoid tissueReproductive ducts & gland epithelium Oral, nasal & anal epithelium Endothelium of blood vessels Thyroid, thymus & parathyroid Tooth enamelSerosaeUrethra & bladder epithelium Pineal, pituitary & adrenal medulla Eye’s fibrous & vascular tunics Respiratory tract epithelium MelanocytesSynovia Flat bones of craniumUrogenital organs ECTODERMMESODERMENDODERM

27. Fetal circulation

28. Pregnancy from the mother’s perspective

29. Hey Ma! It’s getting crowded in here!

30. Labor: the beginning of the end

31. The “let-down” reflex or, more fun with oxytocin