Pregnancy & Human Development Chapter 29 (28)

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.

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

Penetration Secondary oocyte Head of sperm 1650X

No Polyspermy!

Fertilization & First cleavage

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.

Development from zygote to implantation.

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.

Implantation – Day 6

Implantation – Day 7

Hormone levels in early pregnancy

Placental hormones

Implantation

Placentation

Fetus & placenta: 13 weeks

Embryonic Development Differentiation of the three primary germ layers

Germ layer formation, Part II

Neurulation: Part I

Neurulation: Part II

Gastrulation Formation of the primitive gut

Gasturlation part II

Organogenisis in a 5 week embryo

Differentiation of Mesoderm

Differentiation of Mesoderm continued

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

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From embryo to fetus

Fetal circulation

Pregnancy from the mother’s perspective

Hey Ma! It’s getting crowded in here!

Labor: the beginning of the end

A Vertex Presentation…

…and welcome to the world!

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