Pregnancy

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Pregnancy Human Development

• Chapter 29 (28)

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Fertilization Its 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.

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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

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Penetration
Secondaryoocyte
Head of sperm
1650X
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No Polyspermy!
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FertilizationFirst cleavage
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Whats 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.

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Development from zygote to implantation.
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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.

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Implantation Day 6
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Implantation Day 7
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Hormone levels in early pregnancy
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Placental hormones
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Implantation
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Placentation
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Fetus placenta 13 weeks
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Embryonic Development
Differentiation of the three primary germ layers
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Germ layer formation, Part II
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Neurulation Part I
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Neurulation Part II
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Gastrulation
Formation of the primitive gut
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Gasturlationpart II
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Organogenisisin a 5 week embryo
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Differentiation of Mesoderm
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Differentiation of Mesoderm continued
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The Primary Germ Layers
ECTODERM
MESODERM
ENDODERM
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Fig. 29.14a
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Fig. 29.14b
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Fig. 29.14c
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Fig. 29.14d
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Fig. 29.14e
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Fig. 29.14f
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Fig. 29.14g
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Fig. 29.14h
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From embryo to fetus
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Fetal circulation
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Pregnancy from the mothers perspective
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Hey Ma! Its getting crowded in here!
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Laborthe beginning of the end
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A Vertex Presentation
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and welcome to the world!
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The let-down reflexor, more fun with oxytocin