Prenatal DevelopmentChapter 3

FertilizationFertilizationprocess that occurs in the fallopian tubes when the sperm and ova combine to form a zygoteZygotea single cell organism that results from the fertilization of an egg cell by a sperm; the fertilized eggGametes sexual reproduction cellsOvafemale reproductive cellSpermmale reproductive cell

The Germinal Period: 0 2 WeeksBlastocystthe term given to the zygote at about day 5 or 6 postfertilization

Key question 2: What happens in the womb before birth?

Includes the separation of the three germ layers of somatic cellsEnds with the implantation of the gastrula into the uterine wallGerminal period begins with the fertilization of the egg

Ectoderm nervous system (including the brain and spine), skin, nails, and hair, as well as the salivary, pituitary, and mammary glandsEndoderm thyroid gland, bladder, lungs, and digestive systemMesoderm heart, circulatory and lymph systems, connective tissue, muscle, and bonesLayers

The Period of the Embryo: 3 to 8 WeeksEmbryonic period beginning of week 3 and continuing through week 8; organogenesis takes placeOrganogenesis development of major organ systems during the embryonic period; by the end of week 8, 95% of major organs are complete

Third week: The neural plate forms and becomes the brain and neural tube (spinal cord). Neurogenesis, the production of neurons begins. The heart chambers and blood vessels develop.Eighth week: The embryo appears more human, the inner and middle ear develop, and the embryo is the size of a grape.

Embryonic Period

The AmnionThe amnion is one of the life support systems that develops from the trophoblastDevelops from the fertilized egg not from the mothers body

The Period of the Fetus: 9 Weeks to BirthThe period of prenatal development that begins after organogenesis is 95% complete at about week 9 and continues until birth.

Fetal DevelopmentBy 24 weeks: Fat begins to accumulate. Bone marrow begins producing red blood cells. Eyes are fully formed. The fetus is 9 inches long and weighs 21.6 oz.Viability The ability of the fetus to survive outside the womb; at about week 24 to 25.By 40 weeks: The fetus gains 50% of its birth weight in the last month. The skin is smooth. The head has hair. Myelination increases. The fetus is the size of the average newborn: roughly 17 20 inches long and weighing about 7 lbs.

Third trimester

Second trimester

First trimester

Anticipates end; uterus expands to point below breastbone

Less fatigue and nausea; uterus expands into abdominal cavity

Very tired; nausea and pregnancy sickness; breasts change; emotional changes