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Chapter 4


3 Pages

Course Code
PSYC 2450
Anneke Olthof

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Chapter 4: Prenatal Development The Period of the Zygote  After fertilization until implantation into the uterine wall  Cells multiply via mitosis to form a ball-shaped blastocyst  The inner layer (embryonic disk) becomes the embryo  The outer layer develops into tissues that protect and nourish the embryo  Implantation o Burrlike tendrils burrow into the uterine wall and tap into the mother’s blood supply  Development of support systems o Outer layer forms:  Amnion – watertight membrane surrounding the developing embryo, regulates temp and cushions against injury  Chorion – membrane that attches to the uterine tissues to gather nourishment for the embryo  Placenta – an organ, formed from the lining of the uterus and the chorion, that provides for respiration and nourishment of the unborn child and the elimination of its metabolic wastes  Umbilical cord – a soft tube containing blood vessels that connects the embryo to the placenta The Period of the Embryo  From implantation (week 3) to week 8  Ectoderm  Mesoderm  Endoderm  Neural tube forms the brain and spinal cord in the 3 week th  End of the 4 week: heart has formed and is beating, eyes, ears, nose, and mouth begin to form and buds of arms and legs  The second month o Primitive tail forms and disappears o Eyes have corneas and lenses o Ears and rudimentary skeleton o Limbs develop o Brain develops rapidly o Sexual development begins o Circulatory system is running The Period of the Fetus  Last 7 months until birth  Refinement of organ systems  Starts to move, sense, and behave  Third month o Motor actions, swallow, digest, urinate o Sex differentiation  Second trimester (month 4-6) o Movements become more complex and coordinated o Swallow, munch, hiccup, cough, snort o Premature babies have a hard time breathing and suckling o Kicking can be felt, heartbeat can be heard o Bone and cartilage increases o Nails harden, skin thickens, eyebrows, eyelashes, and scalp hair appear o Covered in vernix and lanugo  Third trimester (month 7-9) o Age of viability o Organized cycles of heart rate activity, gross motor activity, and sleepiness/waking activity o Moves head down, gains weight o Uterine musc
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