Chapter 3 - Chapter 3 Prenatal Development Truth or Fiction...

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Chapter 3: Prenatal Development Truth or Fiction? Newly fertilized egg cells survive without any nourishment from the mother for more than a week (T) Your heart started beating when you were only one-fourth of an inch long and weighted a fraction of an ounce (T) If it were not for the secretion of male sex hormones a few weeks after conception, we would all develop external sex organs that look like those of females (T) Fetuses suck their thumbs and hiccup, sometimes for hours on end (T) Parents in wealthy nations have more children (F) The same disease organism or chemical agent that can do serious damage to a 7- week-old embryo may have no effect on a 4-month-old fetus (T) Babies can be born addicted to narcotics and other drugs (T) It is harmless to the embryo and fetus for a pregnant woman to have a couple of glasses of wine in the evening (F) Wanderings: The Germinal Stage What happens During the Germinal Stage? o Germinal Stage is the period from conception to implantation (approximately 2 weeks) o Zygote (single cell formed from the union of the ovum and sperm; repeatedly divides but does not gain in mass; begins to divide into 2 cells within 36 hours and then within another 36 hours, becomes 32 cells o Blastocyst (fluid filled ball of cells)-cell differentiation Blastocyst has two distinct layers inner part called embryonic disk (become the embryo and eventually the fetus) Outer part of the blastocyst- trophoblast (which becomes the placenta, umbilical cord, amniotic sac, and the chorion (lines the placenta)) Early Days of the Germinal Stage o Prior to implantation, the dividing cells are nourished by the yolk of the original egg (ovum) o Nourishment is obtained from the mother once implantation occurs (some bleeding may occur) o Miscarriage (spontaneous abortion) Usually stems from abnormalities in development One-third of all pregnancies result in miscarriage The Embryonic Stage What Happens During the Embryonic Stage of Prenatal Development? o Embryonic Stage begins with implantation (3 rd week) through 8 th week o Major organ systems differentiate o Development follows 2 general trends:
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Cephalocaudal (“head to toe”) – head takes precedence over lower parts of the body; Oversized head shows that the head takes precedence over the growth of the lower parts Proximodistal (“near to far”)- central axis of body outward; growth of organs close to the axis occurs earlier than the growth of the extremities What Happens During the Embryonic Stage of Prenatal Development? o Embryonic disk or Ectoderm (outer layer): develops into nervous system, sensory organs, nails, hair, teeth, and skin o Endoderm (inner layer): forms the digestive and respiratory systems (lungs), liver, and pancreas o Mesoderm (middle layer): develops into the excretory, reproductive and circulatory system, muscles, skeleton, and inner layer of skin o Neural tube : develops into brain and spinal cord (about 21 days) What Happens During the Embryonic Stage of Prenatal Development?
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