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Chapter 4

Chapter 4- Developmental Psyc

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PSYC 2450
Anneke Olthof

Chapter 4: Prenatal Development Prenatal development: All development that occurs between the moment of conception to the beginning of the birthing process, along with the things that can go wrong. Three stages: Zygote (also known as the germinal stage): Lasts from conception until implantation in the uterus wall. Usually lasts from ten to fourteen days. Embryo: Lasts from the beginning to the third week to the end of the eighth week. During this time, virtually all major organs are formed and the heart begins to beat. Fetus: Lasts from the ninth week of pregnancy until the baby is born. All the major organ systems begin to function and the organism develops rapidly. Period of growth. Period of the Zygote: Blastocyst: The ball of cells that is formed when the fertilized egg first begins to divide. Will contain sixty to eighty cells within four days of conception. Inner layers of the blastocyst become the embryo, while the outer layers will develop into tissues that protect and nourish the embryo. Implantation: Six to ten days after conception, the zygote reaches the uterus and burrows small tendrils into the wall, tapping into the mothers blood supply. Takes about 48 hours to complete, occurring 7-10 days after ovulation. Nearly three out of four zygotes fail to survive the initial implantation. Four major support structures to nourish the developing organism: o Amnion: Watertight sac that fills with fluid from mothers tissues. Cushion from blows, regulates temperature, provides a weightless environment making it easier for the embryo to move. o Chorion: a membrane that becomes attached to the uterine tissues to gather nutrition for the embryo. o Placenta: An organ, formed from the lining of the uterus and the chorion, that provides respiration and nourishment of the unborn child and the elements of its metabolic wastes. The villi is a barrier that separates the babies bloodstream and the mothers. It also allows small enough things to pass through, like oxygen and various nutrients, but blood cells are too large to get through. o Umbilical Cord: Soft tube containing blood vessels that connects the embryo to the placenta. How babys main source of oxygen and food get to the embryo. Period of the Embryo: Three layers of the embryonic disk: Outer layer (ectoderm) becomes the nervous system, skin and hair. Middle layer (mesoderm) becomes the muscles, bones and circulatory system. Inner layer (endoderm) will become the internal organs. Period of rapid development. 0.65 cm, Neural tube forms (early spinal cord), heart begins to beat, nose, ears, mouth, eyes begin to form, stubs where legs and arms will be appear. This is the fastest period of development. The second month: becomes more human in appearance. ~2.5 cm, 7 g. Primitive tail appears and then is sealed over. Eyes have cornea and lenses, rudimentary skeleton is formed. Limbs are developing from body outward (arms first, then legs). Rapid brain development. Sexual development happens at eight weeks, genital ridge called indifference gonad, which then changes depending on the sex chromosomes. Circulatory system works on its own, liver and spleen produce blood cells. Period of the Fetus (last seven months) ~9.5 cm, 28 g. Period of rapid growth and refinement of all organ systems. Fetus begins to move sense and behave, unique characteristics develop (facial expressions) Third month: Organs continue rapid growth, become interconnected. Digestive and excretory systems being to work together. Sexual differentiation processes rapidly (testes produce testosterone, which then develop the penis and scrotum, in absence of this, the female genitals form) By the end of the third month, the sex of the baby can be determined Second trimester (Fourth through Sixth months, ~35-38 cm, 0.9 kg): o Week 16-25: Simple movements of the tongue, lips, pharynx and larynx increase, fetus begins to suck, swallow, munch, hiccup, cough, etc. Bone and cartilage increase. Distinctly human appearance, although no possible chance of surviving outside of the womb. o 5-6 months: nails harden, skin thickens, eyebrows, eyelashes and scalp hair appear. o 20 weeks: Functioning sweat glands. Fetus now covered with vernix (white cheesy substance that protects the fetus from chapping from the amniotic fluid) and lanugo (fine hair covering the fetus body that helps vernix stick to the skin. o End of the sixth month: Visual and auditory systems are clearly functional. MEG (magnetoencephalography) has tested this through brain activity. th Third trimester (Seventh through 9 month, ~48-53 cm, 3.2-3.6kg):o All organs mature rapidly. nd th o Age of viability: a point between the 22and 28 prenatal week when survival outside of the womb is possible. o More predictable cycles of heart rate activity, motor activity and sleep cycles. A layer of fat forms under the skin to protect from temperature changes. o Middle of ninth month: Fetal activity decreases and sleep becomes more frequent. External Influences on Prenatal Development Teratogens: External agents such as viruses, drugs, chemicals and radiation that can harm a developing embryo or fetus. Can cause physical deformities, severely retarded growth, blindness, brain damage and even death. o The effects of teratogens on a body part or organ system are worst during the period when that structure is forming and growing most rapidly. o Not all embryos or fetuses are equally affected by a teratogen. Susceptibility to harm is influenced by the genetic makeup and prenatal quality of the embryo, fetus, or pregnant woman. o The same effects can be caused by different teratogens. o A variety of defects can be caused by one teratogen. o Longer expos
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