Life-Span Development Chapter 3- Prenatal Development and Birth

embryonic period

-2-8 weeks after conception -events: rate of cell differentiation intensifies, support systems for the cell form, organs appear -begins as blastocyst attaches to uterine wall

prenatal development timeline

-266-280 days (38-40 weeks) -three periods: germinal, embryonic, and fetal

fetal period

-about 7 months -prenatal period between two months after conception and birth in typical pregnancies -growth and development continue dramatically

when is a fetus first viable

-as early as six months (24-25 weeks after conception) -usually need help breathing

implantation

-attachment of zygote to the uterine wall -about 11-15 days after conception

amnion

-bag of clear fluid in which the developing embryo floats -provides temperature and humidity controlled environment -shock-proof

embryo

-blastocyst after it has attached to uterine wall

umbilical cord

-connects baby to placenta through two arteries and one vein

placenta

-disk-shaped group of tissue in which small blood vessels from the mother and offspring intertwine but do not join

maternal alcohol use

-ethanol crosses the human placenta

germinal period

-first two weeks after conception -events: zygote created, cell division, attachment of zygote to uterine wall

blastocyst

-group of cells -formed by mitotic zygote divisions during germinal period -formed after ~1 week -contains inner mass of cells that eventually develop into the embryo

organogenesis

-organ formation that takes place during the first two months of prenatal development -during formation, especially vulnerable to environmental chagnes

trophoblast

-outer layer of cells in blastocyst -provides nutrition and support for the embryo

large molecules that cannot pass through placental wall

-red blood cells -harmful substances (bacteria, maternal waste, hormones)

nutrient flow between placenta and mom

-small molecules pass back and forth between the mother and the embryo or fetus -drugs or chemical substances ingested by mother can cross placenta to a degree, unless too large to pass, metabolized, or altered

cigarette use

-smoke weakens and increases the oxidative stress of fetal membranes from which the placenta develops

trimesters

-three equal periods of three months -not the same as prenatal periods -first trimester (0-3 months); contains germinal and embryonic periods, fetal period begins -second trimester (3-6 months); fetal period, viability occurs at end -third trimester (6-9 months); contains fetal period

development tracker

-week 3- neural tube forms, eyes start appearing (21 days), heart cells begin differentiation (24 days) -week 4- urogenital system develops, arms and leg buds emerge, heart and vessels start appearing -week 5-8- arms and legs differentiate further, face starts forming, intestinal tract develops, facial structures fuse -week 8- 1/30 ounces and just over 1 inch long

life support systems for embryo

1) amnion 2) umbilical cord 3) placenta -develop from fertilized egg, not the mother's body

embryonic layers

1) endoderm (innermost)- becomes digestive and respiratory systems 2) mesoderm (middle)- becomes circulatory system, bones, muscles, excretory system, reproductive system 3) ectoderm (outermost)- nervous system, brain, sensory receptors, skin parts -every body part develops from these three layers

conception

when a single sperm cell from the male unites with an ovum (egg) in the female's Fallopian tube in a process called fertilization