two germ cells in humans
sperm and ovum
explain meiosis
cell division resulting in germ cell containing 23 chromosomes
how many average sperm are released during sex? how many make it to the egg? how long does it take?
- 500 milli
- 200
- 6-7 hours
zygote
- fertilized egg
- occurs in upper third portion of fallopian tubes
three main stages of prenatal development
- germinal period (weeks 0-2)
- embryonic period (weeks 3-8)
- fetal period (weeks 9-birth)
what period does the zygote divide rapidly
germinal
Approximately ________ after fertilization, the zygote enters the uterus from the fallopian tube.
4-5 days
blastocyst
- further developed version of zygote
- forms as a hollow ball of cells
- implants into walls of uterus
- when fully formed (1 week), shows the end of germinal period
what with the embryonic period
- cell differentiation
- organ systems forming
- by the end: bodily systems are functioning
what pattern of dev does embryonic dev follow
- cephalocaudal
- areas near head dev first
embryonic layers
- ectoderm (becomes nervous system, nails, teeth, inner ear, eye lens, epidermis)
- mesoderm (becomes muscles, bones, circulatory system, skin)
- endoderm (becomes digestive system, lungs urinary tract, glands)
what period does the neural tube form?
- embryonic
- created when ectoderm folds in on itself=u shaped groove
embryo support system
- amnoitic sac (protective liquid sac, where embryo floats, maintains constant temp)
- placenta (protective, allows for nutrients, oxygen + waste to pass through, prevents mom’s blood mixing w baby’s blood)
when does the fetus becomes more active? when can the mom feel the fetus?
- fetal period
- 11-12 weeks
- can be felt at 16 weeks
when does fetus begin putting on weight and facial expressions
- 20 weeks
what is the age of viability
- 23 weeks, when brain and lungs are developed enough for survival w out major medical intervention
what three aspects make up the fetal experience?
- movement (active fetus=active newborn)
- sensory experiences (visual, taste, tactile, auditory, smell)
- learning (habituation and dishabituation)
when do all the major organ systems become fully integrated w one another
fetal period
cell division that produces germ cells
meiosis
the outermost layer of cells of an embryo in early development, which includes nerve cells
ectoderm
a support organ for the fetus that consists of semi-permeable membrane
placenta
the middle layer of cells of an embryo in early development, which includes the bones
mesoderm
the innermost layer of cells of an embryo in early development, which includes the lungs
endoderm
what period ends at implantation
germinal
