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prenatal development and birth

prenatal development and birth - Chapter 40 Prenatal...

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Chapter 40- Prenatal Development and Birth Germinal period- first 14 days Embryonic period- 3 rd through 8 th week Fetal period- 9 th week through birth Conception- once a month an ova is released and it goes down the fallopian tube. If there are sperm present the odds are really good that it will be penetrated in the curve of the fallopian tube. The egg is fertilized and it begins to immediately divide. It takes several days to make a trip to the uterine wall. If it is successful and everything goes right the egg will get implanted. Germinal- zygote divides and keep dividing, at least through the 3 rd doubling they are all the same. At the stage of 8 cells, differentiation begins. The early stem cells take on distinct characteristics and they gravitate to locations, foreshadowing the type of cells they will become At about a week after conception the multiplying cells separate into two separate masses. The outer layer forms a shell, which later becomes the placenta, and the inner cells form a nucleus, later the embryo. The first task of out cells is to achieve implantation-imbed themselves into the nutrient environment of the uterus 60% of all natural conceptions fail to implant, 70% of in vitro procedures fail to implant. Embryo- from the third to the eighth week First sign of human structure- thin line down the middle (22 days) that becomes the neural tube, which eventually forms the central nervous system, including brain and spinal column Fifth week- arm and leg buds appear. Tail-like appendage extends from the spine 8 th week- embryo weighs 1 gram and is 1 inch long, head more mounded, face formed All basic organs and body parts except for sex are present 20% of all embryos spontaneously abort now Fetus- from the ninth week until birth Third month- sex organs take shape- y cell sends signal to male sex organs, for females, no signal occurs Genital organs are fully shaped by 12 th week All body parts are present Fetus can move every part of the body Fetus weighs three ounces and is 3 inches long Middle 3 Mos- preparing to survive Heartbeat is stronger Digestive and excretory systems develop more fully Impressive brain growth- 6x in size and responsive
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New neurons develop- neurogenesis Synapses- connections between neurons- synaptogenesis Age of viability- age at which preterm baby can possibly survive- 22 weeks.
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