Human Development

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

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

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

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

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

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

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