Pregnancy - time from fertilization until infant is born
Conceptus - developing offspring
Embryo - period of time from fertilization until week 8
Fetus - week 9 until birth
Gestation period - from date of last period until birth (approx. 280 days)
For fertilization to occur, sexual intercourse must occur no more than 2 days before ovulation and no later than 24 hours after.
Zygote - first cell of a new individual
Cleavage - rapid series of mitotic divisions that begin with the zygote
Embryonic Development:
Zygote - first cell of a new individual; begins cleavage 24 hours after fertilization
Morula - a ball of 16 cells that forms 3 days after ovulation
Blastocyst - a ball of 100 cells; secretes human chorionic gonadotropin (hCG) to induce the corpus luteum to continue producing hormones; attaches to the endometrium 7 days after ovulation
Functional areas of the blastocyst:
Trophoblast - large fluid-filled sphere
Inner cell mass - cluster of cells to one side
Primary germ layers of the blastocyst:
Ectoderm - outside layer, gives rise to nervous system and epidermis
Mesoderm - middle layer, gives rise to everything else
Endoderm - inside layer, forms mucosae and associated glands
Amnion - fluid-filled sac that surrounds the embryo
Umbilical cord - blood vessel-containing stalk of tissue that attaches the fetus to the placenta
Placenta - forms a barrier between mother and embryo; delivers nutrients and oxygen