Human Development

1
Human Development
2
Fertilization

• Must occur within 24hrs postovulation
• Requires capacitated sperm (6-8hrs)
• Secondary oocyte completes Meiosis II once sperm
  enters oocyte
• Zygote formed with fusion of male and female
  pronuclei

3
Cleavage

• Rapid mitotic cell division of zygote
• 2-cell stage 36 hours
• 4-cell stage 48 hours
• 8-cell stage 72 hours
• Morula - solid ball of cells (blastomeres) at 96
  hours
• Takes 4-5 days to travel from uterine tubes to
  uterine cavity

4
Implantation

• Morula develops into bastocyst, a hollow ball of
  cells differentiated into inner cell mass and
  trophoblast
• Trophoblast embeds into endometrium
• secretes enzymes, HCG
• chorionic villi
• attachment occurs 7-8 days after fertilization

5
Embryonic Development

• Extends from the 2-8th week after conception
• Inner cell mass differentiates into
• Ectoderm - epidermis of skin, entire nervous
  system
• Endoderm - functional lining of the digestive and
  respiratory system
• Mesoderm - forms muscle, bone, blood vessels, and
  kidneys

6
Fetal Membranes

• Chorion - fetal part of the placenta, outermost
  membrane
• Amnion - fluid filled sac covering embryo and
  later fetus
• Yolk sac - source of nourishment for embryo
  early site of blood formation
• Allantois - developing umbilical cord and
  developing bladder of fetus

7
Placenta Formation

• Functions to exchange waste products and blood
  gases
• Chorionic villi penetrate into the decidua
  basalis of the endometrium
• Chorion - fetal portion
• Decidua basalis - maternal portion
• Placenta previa

8
Hormones of Pregnancy

• HCG secreted by the chorion maintains corpus
  luteum
• FSH repressed, cycle stops
• Progesterone maintains endometrial lining
• Placenta secretes estrogen and progesterone
• Corpus luteum degenerates
• Late pregnancy relaxin secreted