Physiology 1 2003 Topic 10: Reproduction

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Physiology 12003Topic 10 Reproduction

• Ref Germann Stanfield (2002) Chapter 21

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Reproduction 3 Pages 695-705Objectives

• Describe the regulation of estrogen
  progesterone secretion during pregnancy
• Explain how these hormones help maintain
  pregnancy
• Explain how these hormones prepare body for
  parturition
• Explain milk production ejection

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Fertilization, Implantation Pregnancy

• Timing of fertilization
• Sperm remain viable in the female reproductive
  tract for 5 days. Ova remain viable for 12-24
  hours after ovulation.

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Fertilization

• Sperm penetrates corona radiata
• (granulose cells around secondary oocyte)
• Binds to specific protein in zona pellucida ?
  Enzymes released by acrosome (Acrosome reaction)
  digest a path through zona pellucida
• Sperm binds to receptor on oocyte plasma
  membrane, fusing with plasma membrane
• Sperm enters oocyte ? resumes meiosis ? ovum
• Sperm plasma membrane both nuclear membranes
  disintegrate
• Sperm ovum chromosomes combine ? zygote

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• Fusion of sperm with ovum membrane ?
• Exocytosis of vesicles near ovum surface
  releases enzymes between membrane zona
  pellucida ? Zona pellucida hardens pulls sperm
  away from membrane
• ? Block to Polyspermy

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Early Embryonic Development Implantation

• Zygote ?Morula (ball of cells) ?
• Blastocyst Trophoblast Inner cell mass
  Blastocoele
• Blastocyst attaches to endometrium
• Trophoblast enzymes digest path into
  endometrium
• Paracrines from trophoblast ? endometrial
  capillaries
• Placenta develops from maternal ( endometrium)
  embryonic (trophoblast) tissue

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Stages of early embryonic development
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Early late implantation
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Later Embryonic Fetal Development

• Amniotic cavity develops within inner cell mass
• Inner cell mass ? Embryo
• Trophoblast ? Chorion
• Cells around amniotic cavity
• ? amniotic sac
• Amniotic fluid surrounds embryo
• Embryo ? fetus _at_ 8 weeks

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Later Embryonic Fetal Development

• Chorionic villi digest into maternal tissue
• Exchange (nutrients, wastes, gases) occurs
  between fetal capillaries in chorionic villi
  maternal blood around villi
• One umbilical vein conveys blood to fetus
• Two umbilical arteries return blood to placenta

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Growth development of embryo supporting
structures
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The Placenta
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Hormonal Changes During Pregnancy

• Trophoblast secretes human chorionic
  gonadotropin hCG early in pregnancy
• hCG mimics LH thus maintains corpus luteum.
• Corpus luteum ? Estrogens Progesterone, which
  prevent menstruation thus maintain pregnancy
• Chorionic portion of placenta later ? hCG
• Placenta later ? Estrogens Progesterone, so
  hCG not required, hCG production ?

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Plasma hormone concentrations during pregnancy
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Effects of Estrogen

• Growth of duct tissue fat deposition in breasts
• Anterior pituitary ? Prolactin ?breast growth
• ?Uterus growth ? responsiveness to oxytocin

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Role of hCG in regulating estrogen progesterone
secretion by the corpus luteum in early pregnancy
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Effects of Progesterone

• Growth of glandular tissue in breasts
• ?uterine smooth muscle contractions?aids
  implantation prevents expulsion of embryo or
  fetus
• Maintains secretory phase uterine conditions eg ?
• Blood vessels proliferate
• Endometrial glands? glycogen ? energy.
• Viscous cervical secretions plug the cervix
• ?Plasma progesterone prevents menstruation

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Parturition Lactation

• ? levels of estrogens overcome the ability of
  progesterone to suppress uterine contractions
• Breakdown of collagen softens cervix
• Wt of Fetus? uterine stretching? contractions
• Amniotic sac ruptures
• Uterine contractions push fetus downwards,
  dilating cervix stimulating stretch receptors

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Parturition Lactation

• Stretching ? neural stimulation of posterior
  pituitary ? oxytocin? ? uterine contractions
• Stretching, etc
• ie ve feedback.

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Dilation of cervix
Position of fetus before parturition
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Movement of fetus through birth canal
Expulsion of placenta
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Milk produced by alveoli (clusters of sac-like
glands) Suckling ? Contraction of myoepithelial
cells Compresses alveoli, ejecting milk through
ducts
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Hormonal regulation of lactation in response to
suckling