Chapter 4 Flashcards
3 major phases of prenatal development:
Period of the zygote / germinal period: conception through implantation (10-14 days)
Period of the embryo: beginning of 3rd week through end of 8th.
Period of the fetus: 9th week of pregnancy to birth
Period of the zygote
Fertilized ovum (zygote) moves down Fallopian tube toward users, while dividing by mitosis into 2 cells.
Those 2 cells and all resulting ones continue to divide, forming a ball (blastocyst).
Inner layer of blastocyst, called embryonic disk, becomes embryo. Outer layer of blastocyst will develop into tissues that protect and nourish embryo.
Implantation:
As blastocyst approaches uterus 6-10 days post conception, tends emerge from over surface; burrowing into uterine wall, tapping nom’s blood supply.
Takes about 48 hours.
Looks like small translucent blister on wall of uterus.
Development of support -systems after implantation:
Blastocyst forms 4 major support structures:
Amnion: watertight sac that fills with fluid from mom’s tissues. (amniotic fluid) cushions against blows, regulates temp., provides weightless environment (easier for embryo to move)
Floating in amnion is yolk sac - produces blood cells until embryo can make its own.
Chorion: surrounds amnion, eventually becomes lining of placenta.
Allantois: forms umbilical card.
Placenta:
Organ formed from lining of uterus and the chorion; provides respiration + nourishment + elimination of waste.
Is fed by blood vessels from mom & embryo; has villi to prevent these 2 bloodstreams from mixing.
Semipermeable
Embryonic disk differentiates into 3 cell layers by 3rd week:
Ectoderm (outer layer): will become the nervous system, skin, and hair.
Mesoderm (middle layer): will become the muscle, bones, and circulatory system.
Endoderm (inner layer): will become the digestive system, lungs, binary that, pancreas, liver, etc.
Neural tube:
Primitive spinal card that develops from the ectoderm and becomes the CNS.
Second month of embryo:
- grows 1mm per day
- primitive tail appears, gets enclosed by tissue, and becomes the coccyx.
- by middle of 5th week, eyes have corneas+ lenses
- by 7th week, ears are formed & embryo has rudimentary skeleton
- bran develops rapidly
-during 7th & 8th week, sexual dev. begins with genital ridge called indifferent gonad
^ if male; testes produced. Female, ovaries
Period of the fetus
- Last 7 months of pregnancy
- period of rapid growth & refinement of all organ systems
- all major organ systems begin to function
- fetus begins to move, sense, behave
- individuality emerges
3rd month:
Organ systems continue growing, become interconnected
Sexual diff. progresses rapidly
By end of 3rd month sex can be detected by ultrasound
What is vernix? Lanugo?
Vernix = white, cheesy substance on fetus skin to protect from chapping
Lanugo = fine body hair, helps vernix stick to skin
Age of viability:
Btw 22nd & 28th prenatal weeks.
Teratogens:
External agents, such as viruses, drugs, chemicals, and radiation, that can harm a developing embryo or fetus.
Rubella:
Has little effect on mom but can cause serious birth defects in unborn babies who are exposed in first 3-4 months of pregnancy
Critical periods of prenatal Dev:
Period of dividing zygote + implantation: usually not susceptible to teratogens
Embryonic period:
-week 3: CNS, heart
-week : eye, heart, arm, leg, ear
-week 5: eye, heart, arm, leg, ear
-week 6: heart, ear, CNS,
-week 7: CNS, eyes, palate, external genitals, ear
-week 8: CNS, eyes, teeth, palate, external genitals, ear
Fetal period:
-week 9: CNS, external genitals, ear
