)- the environment surrounding birth. What is a:morula-mass of 16 cellsblastula/blastocyst- a hollow ball of about 150 cells that is the size of the head of a pin What occurs during the embryo/embryonic period, fetus/fetal period (Table 4.3), p. 94, (Know ZEF)? Zygote- fertilized egg1.germinal period: conception to 2 weeksa.dividing mass of cellsb.once every 24 hours 2.implantation: 50% fail3.zygote -> morula -> blastulaEmbryo- 3 weeks to 8 weeks: through 2 months1.amnion- watertight membrane that fills with fluid that cushions and protects the embryo2.chorion- a membrane that surrounds the amnion and attaches rootlike extensions called villi to the uterine lining to gather nourishment for embryo3.placenta- a tissue fed by blood vessels from the mother and connected to the embryo by the umbilical cord4.heart beats at 4 weeks5.internal sex differentiation: 7-8 weeks6.eyes, ears, nose, mouth and limbs buds and 2 months7.organogenesis- process in which every major organ takes shapeWhat occurs during the fetal period (p. 96-99, Table 4.3)?Fetus- 3 months1.neurons proliferate, migrate and differentiatea.myelination develops2.organ systems grow and function3.bones systems grow and function4.bones and muscles develop- movement is felt What occurs during the zygote/germinal period (Table 4.1, p. 93)1.fertilization usually occurs within 24 hours
2.the single celled zygote begins to divide 24-36 hours after fertilization3.the mass has 16 cells and is called a morula, it is travelling down the fallopian tube to the uterus4.““5.an inner cell mass forms, the entire mass is called a blastocyst and is the size of a pinhead6.the blastocyst attaches to the wall of the uterus7.““8.the blastocyst becomes fully embedded in the wall of the uterus. It now has 250 cellsWhen is the blastocyst fully embedded in the uterine wall? – 4 weeksDefine placenta- sac that , umbilical cord, HCG- secreted by the placenta after implantation to prevent the uterus lining and supplies another hormone that prevents menstruationEctoderm- the outermost of the three germ layers of the embryoMesoderm-middle layerEndoderm- innermost layerAccording to your text, how far along in gestation is the age of viability (p. 98)- at about 23 weeks after conceptionWhat is a critical period (p. 101)- defined period in the development of the organism when it is particularly sensitive to certain environmental influencesa teratogen (p. 101-110)-any disease, drug, or other environmental agent that can harm a developing fetus. Thalidomide:-Thousands of pregnant women who used thalidomide (mild tranquilizer used torelieve morning sickness) gave birth to babies with all or parts of their limbs missing (flipper limbs)oGave birth to critical periods for deformities Alcohol:-Alcohol readily consumed crosses the placenta, where it can directly affect fetaldevelopment in various ways oSymptoms include neuronal death, impaired functions of glial cells or Fetal Alcohol Syndrome (FAS)Some noticeable symptoms are small head and distinctive facial abnormalities, smaller and lighter in weight, most importantly signs of CNS damage.