Pregnancy and Childbirth

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Mature ovum (ovulated secondary oocyte)
corona radiata follicle cell layer surrounding
secondary oocyte zona pellucida glycoprotein
layer surrounding ovum (only one sperm gets
through)
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• Process of Fertilization
• Sperm swim from vagina, up cervix, up endometrial
  lining and into fallopian tube
• If female is near the middle of her menstrual
  cycle, then a secondary oocyte may be present
• Typical location for fertilization is in the
  fallopian tube many sperm work to get through
  corona radiata
• 1. Sperm that make it to zona pellucida compete
  to get into ovum (only one gets in) by secreting
  enzymes held in their acrosomes
• 2. First sperm to get through has its plasma
  membrane fused with ovums plasma membrane (this
  initiates cortical reaction)

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• Cortical Reaction
• In cytoplasm of ovum (all around plasma membrane)
  are small vesicles called cortical granules
• When the 2 gametes fuse their plasma membranes,
  the cortical granules fuse with the ovums
  membrane and secrete enzymes to the outside
• The enzymes cause a chemical change in zona
  pellucida making it impermeable to sperm
• Note this happens immediately after first sperm
  enters to ensure that only one sperm fertilizes
  egg

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• Pregnancy
• I. Early Embryonic Development
• first mitotic division 24 hrs after
  fertilization
• by the time the fertilized egg (zygote) reaches
  the uterus and is ready for implantation in the
  endometrium it is 100 cells (7 days later)

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• embryo at this stage is a blastocyst
• - outer cells become the placenta
• - inner cells will become the embryo

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• II. Early Pregnancy
• If implantation occurs then embryo will secrete
  its own hormone, HCG (human chorionic
  gonadotrophin)
• The HCG gets into moms bloodstream and targets
  the corpus luteum it stimulates the corpus
  luteum to continue secreting progesterone so the
  endometrium stays in tact

Positive pregnancy test indicated by presence of
HCG (this is only made by embryo)
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• III. Role of the Placenta
• After implantation, the blastocyst (outer layer)
  and moms endometrium form the placenta
• Growing embryo requires nutrients and therefore a
  connection between mom and fetus requires
  placenta and umbilical cord
• Later in pregnancy placenta secretes hormones
• Umbilical cord contains 3 blood vessels
• 2 vessels carry blood from fetus to placenta
  (these are deoxygenated and contain waste
  products)
• 1 vessel carries blood from placenta to fetus
  (oxygenated with nutrients)

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Materials from fetus to mom via placenta Materials from mom to fetus via placenta
Carbon dioxide Oxygen
Urea Nutrients (e.g., glucose, amino acids)
Water Water
Hormones (e.g., HCG) Hormones
Vitamins, minerals
Alcohol (why we dont drink when pregnant)
Some viruses (measles, HIV)
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Note At no time does the blood of the fetus and
the blood of the mother actually mixall
molecular exchanges occur via active/passive
transport in placenta
Note Placenta also takes over job of secreting
estrogen and progesterone to keep
endometrium/blood supply available to fetus
(corpus luteum is now gone)
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• Some tissue of developing embryo is used to make
  amniotic sac
• Within the sac is amniotic fluid the fetus
  floats in this fluid
• Functions of amniotic fluid
• Providing cushioning in case of blunt force
  trauma to abdomen
• Allows fetus free movement for muscle and
  skeletal development
• Thermal stability
• Note this is the fluid sampled during
  amniocentesis

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• The Process of Birth
• 1. Progesterone levels drop
• 2. Oxytocin secreted from pituitary gland levels
  increases after each contraction which causes
  contractions to get more frequent and more
  intense (this is known as positive feedback and
  it only stops once the uterus has nothing to
  contract on) (Pitocin used to induce labor)
• Cervix dilates to 10cm
• Babies typically born head first, face down
  (otherwise called breech)
• After baby, moms push out afterbirth (placenta)
• Lactation (breast milk production) begins soon
  after birth