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Chapter 4

Chapter 4

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Psychology 2040A/B

Psych 2040a Chapter 4: Prenatal Development, Birth, and Newborns Readiness for Life Prenatal Development: the development that occurs between the moment of conception and the beginning of the birth process. From Conception to Birth prenatal development is divided into 3 major phases: period of the zygote (germinal period) period of the embryo - usually from the 3rd to 8th week period of the fetus - usually from the 9th week to the pregnancy The Period of the Zygote zygote (ovum + sperm) moves down the fallopian tube towards the uterus - undergoes through mitosis a blastocyst is formed (a ball shaped structure) that will contain 60-80 cells within 4 days of conception inner layer of the blastocyst contains the embryo (is called the embryonic disk before it attaches to the uterus wall) Implantation implantation: the burrowing of the blastocyst into the uterus lining; burrowing taps into the mothers blood supply there is a specic window of implantation - usually takes about 48 hours and around 7-10 days after ovulation Development of Support Systems the blastocysts outer layer rapidly forms 4 major support structures for the embryo amnion: watertight membrane that surrounds the embryo, regulating its temperature and to cushion it against injuries (amniotic uid) chorion: membrane that surrounds the amnion and is attached to the uterine later to gather nourishment the lining of the chorion eventually becomes the lining of the placenta - a multipurpose organ that provides respiration and nourishment of the unborn child and elimination of its metabolic wastes umbilical cord (allontois): soft tube containing blood vessels that connects the embryo to the placenta Purpose of the Placenta purpose is to deliver nutrients such as oxygen, glucose, proteins, and carbon dioxide to the embryo, coming from the mother also transfers waste products from the embryo to be eliminated The Period of the Embryo usually from the 3rd to the 8th week of pregnancy the embryonic disk in the blastocyst is rapidly differentiating into 3 layers: ectoderm - becomes the nervous system, hair, and skin portion of the ectoderm folds into a neural tube: the primitive spinal cord that eventually forms the CNS mesoderm - muscles, bones, and circulatory system endoderm - digestive system, lungs, urinary, and other vital organs by the end of the 4th week, there is a heartbeat The Second Month becomes much more human in appearance grows about 1mm per day features such as hands, ears, eyes, and limbs develop by the end of the 2nd month brain develops during this period as well during the 7th and 8th weeks, the embryos sexual development begins with the appearance of a genital ridge called the indifferent gonad if the embryo is male, a gene on its Y chromosome triggers a biochemical reaction that instructs the gonad to produce testes. if it is a girl, the gonad receives no instructions and will produce ovaries by the end of the 2nd month, the circulatory system is fully formed The Period of the Fetus period of rapid growth and renement of the organ systems The Third Month organ systems become interconnected by the end of the 3rd month, the sex of the fetus can be determined systems work together to perform functions (ie. baby kicking) The Second Trimester: The 4th - 6th Months simple movements of the tongue, pharynx, and larynx increase in complexity fetus begins to suck, hiccup, swallow, cough, and snort hardening of the skeleton also takes place by the end of the 16th week, the fetus has a human-like appearance, but still has no chance of prematurely surviving 5th-6th months: nails harden, skin thickens, and eyebrows/lashes/scalp hair begins to appear 20 weeks: sweat glands are functioning fetus is covered with vernix (white cheesy substance that covers the fetus to protect the skin from chapping) and lanugo (ne hair covering the fetuss body to help the vernix stick to the skin) by the end of the 6th month, the fetuss visual and auditory senses are fully intact The Third Trimester: The 7th - 9th Months somewhere in between 22-28 weeks after conception (usually in the 7th month), the fetus reaches the age of viability (the point in which the fetus can start surviving outside the uterus) fetuses who are premature usually still need oxygen assistance since the pulmonary alveoli in their lungs are too immature to inate and exchange oxygen for carbon dioxide on their own fetuses are eventually positioned for labor in which it positions the head into the gap between the pelvic bones to be pushed throughEnvironmental Inuences 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 the effects of a teratogen on a body part or organ system are worst during the period when that structure is forming and growing most rapidly sensitive period: each system has a different period 3rd-5th week: most crucial period for gross physical defects of the head and central nervous system the heart is vulnerable from the middle of the 3rd through the 6th week same defect can be caused by different teratogens variety of defects can result from a single teratogen long-term effects of a teratogen can depend on the postnatal environment some teratogen cause sleeper effects that may not be apparent until later in life teratogens can have subtle effects on babies behaviour that are not obvious at birth but can inuence their psychological development Maternal Diseases some disease agents can cross the placental barrier - can affect an embryo that has an immature immune system Rubella (German measles) a disease that has little effect on the mother but may cause a number of serious birth defects in unborn chi
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