Fertilization and Germ Layers Notes (PDF)

Fertilization to Implantation 1) Ovulation 2) Fimbraie sweep egg to fallopian tube where fertilization occurs to create a zygote. The acrosome allows the sperm to get through the egg’s protective barriers. Only the contents of the head of the sperm enter the egg to form a...

Fertilization to Implantation 1) Ovulation 2) Fimbraie sweep egg to fallopian tube where fertilization occurs to create a zygote. The acrosome allows the sperm to get through the egg’s protective barriers. Only the contents of the head of the sperm enter the egg to form a zygote. FYI  3) The zygote undergoes a number of cellular divisions on its way to the uterus 4) Cleavage: cell division without any cell growth (cells do not get larger) until the morula is formed (ball of cells) 5) Blastocyst: cells move around to create an outer ring of cells and an inner mass. (around day 5)  6) Implantation: The blastocyst then attaches to the endometrium wall (around Day 7) – see handout  Development The outer layer of the blastocyst produces three membranes: chorion: finger – like projections implant into endometrium and are the fetal contributions to the placenta. Projections called chorionic villi create a large surface area between maternal and fetal blood supplies. hCG – human chorionic gonadotropic hormone is produced. It maintains the corpus luteum for the 1st 3 months until the placenta is fully functioning and can produce estrogen and progesterone. Pregnancy tests identify HCG in the urine of a woman. b. amnion: creates a protective sac that encloses the fetus in a fluid (amniotic fluid) filled environment. Acts to: cushion the fetus and prevents temperature fluctuations while allowing freedom of movement  Further Development Gastrulation (Occurring about day 15): The process of the inner layer cell mass forming the different germ layers, creating a 3 layer structure called a gastrula.  Germ Layers – table 1 p. 532 Ectoderm – forms skin, hair, nails, sweat glands, nervous system, eyes, ears, teeth, mouth lining Mesoderm – forms muscles, blood vessels & blood, kidneys & reproductive structures, connective tissue, cartilage & bone Endoderm – forms liver, pancreas, thyroid, bladder, lining of digestive system & respiratory tract  FYI - Various Teratogens Cigarette Smoke – constricts fetus’s blood vessels, preventing the fetus from receiving enough oxygen Alcohol – affects the fetus’s brain, CNS, and physical development Prescription medications – antibiotics, acne medications, anti-thyroid drugs, and anti-cancer drugs, thalidomide