Berk p. 60-77

7 Pages

Health Sciences
Course Code
Health Sciences 2711A/B
Treena Orchard

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HS 2700A September 28, 2009 Readings Berk pp. 60-77 • ovum is a tiny sphere, measuring 1/175 inch in diameter • although it is invisible to the naked eye, it is a giant to the microscopic world. • sperm is 1/500 inch • if the ovum is not contacted by the sperm, pregnancy does not occur and it is discarded 2 weeks later by menstruation. • sperm is produced 300 million a day in the testes • sperm live up to 6 days and can lie and wait for the ovum • corpus luteum: the spot on the ovary from which the ovum was released • secretes hormones that prepare the lining of the uterus to receive a fertilized ovum. • ovum only survives for 1 day after being released into the fallopian tube • 38 weeks of pregnancy divided into three stages: • zygote • embryo • fetus • Zygote: • lasts about 2 weeks (from fertilization in the fallopian tube until the cell is released into the uterus) • by the 4th day, 60-70 cells fill the hollow, fluid-filled ball called a blastocyst • inside the blastocyst, are embryonic disks, which are the cells inside • the outer ring of cells are called the trophoblast • Implantation: between 7th and 9th days after fertilization, this is when the blastocyst buries itself deep into the uterus lining. • trophoblast multiples and forms a membrane called the amnion, that closes the organism in amniotic fluid (helps keep temperature and provides cushion) • yolk sac emerges and produces red blood cells until the liver, spleen, and the bone marrow are mature enough to take over this function. • 30% of zygotes do not survive these first 2 weeks • The Placenta and the Umbilical Cord: • trophoblast forms another membrane called the chorion, where tiny blood vessels (villi) emerge. • as the villi buries itself into the uterine wall, the placenta forms. • placenta permits food and oxygen to reach the organism and waste products to be carried away • placenta is connected to the organism by the umbilical cord (contains one large vein, and two arteries) • vein: delivers blood with nutrients • arteries: remove waste products • Embryo: • last from implantation to the 8th week of pregnancy (in a span of 6 weeks) • groundwork of all body structures and organs are done • The Last Half of the First Month: • in the first week of this period (3rd week of the month) the embryonic disk forms three layers of cells: • ectoderm --> nervous system and skin • mesoderm --> muscles, skeleton, circulatory system, and other internal organs • endoderm --> digestive system, lungs, urinary tract, and glands • ectoderm folds over to become the neural tube --> spinal cord and brain • neurons form, heart begins to pump blood, and the muscles, digestive tract, backbone, and ribs appear • embryo is only 1/4 inch long at this point • The Second Month: • the eyes, ears, nose, jaw and neck form • intestines grow, heart develops separate chambers • liver and spleen take over the production of making red blood cells • embryo can now move, but still too tiny to be sensed by the mother • Fetus: • 9th week to the end of the pregnancy • The Third Month: • brain starts to signal, fetus starts to kick, bend its arms, etc • tiny lungs start to work • by 12th week, external genitals begin to form, sex of fetus can be determined • heartbeat can now be heard • 1st trimester of the pregnancy is complete at the end of the 3rd month • The Second Trimester: • between 17-20 weeks • vernix forms - protects skin from chapping during the long months spend bathing in the amniotic fluid. • lanugo forms - white, downy hair covering the entire body, helping the vernix stick to the skin • brains neurons are in place • organs are well-developed • glial cells are still forming (still continues to even after birth) • brain growth = new behavioural capacities • The Third Trimester: • age of viability - the point at which fetus can first survive, between 22 and 26 weeks • cerebral cortex enlarges • greater responses to stimulation • temperament begins (fetus may get a fever = active in first year of life) • during the final two months, fetus can distinguish tone and rhythm • gains 5 pounds and grows 7 inches • Teratogens: an environmental agent that causes damage to the baby during the prenatal period • harm of the teratogen is dependent on dosage, heredity, age, and other negative influences. • it is during the embryonic period that the teratogens have the most affect in • Thalidomide: morning sickness drug, taken by mothers during the embryonic period (4-6 weeks into pregnancy) • produced deformities to the limbs, damaged the ears, heart, kidneys and genitals • children performed lower in intelligence tests, perhaps impacted the nervous system • Diethylstilbestrol (DES): prescribed to prevent miscarriages, but high rates of vaginal cancer, malformations of the uterus, and infertility. • for men, cancer of the testes, and abnormalities of the genital area • Accutane: vitamin A derivative used to treat acne • eye, ear, skull, brain abnormalities • Aspirin: low birth weight, infant death around time of birth, poorer motor development, and lower intelligence scores • heavy caffeine intake is also associated with many things • Illegal Drugs: cocaine, heroin, or methadone (a less addictive drug, alternative to heroin) • prematurity, low birth weight, physical defects, respiratory distress, and death. • infants are born drug-addicted • feverish, irritable, and cries are abnormally shrill • crack-babies are usually have constricted blood vessels, thus oxygen delivery is shortened • marijuana has been linked to low-birth rate, and a smaller head size. Also linked to attention, memory, and academic achievement difficulties. • Tobacco: 17% of Canadian women smoke during their pregnancy • most common effect is low birth weight. • some effects include: miscarriage, prematurity, impaired heart rate and breathing, infant death, asthma, and cancer later in childhood • although some babies appear to be physically healthy, there may be some abnormalities that underly such as less attentive to sounds, displaying more muscle tension, and are more excitable when touched/stimulated. • not only does nicotine constrict the blood vessels, it also raises carbon monoxide in the blood stream which replaces red blood cells, and damages the nervous system. • Alcohol: mothers who drink heavily during their pregnancy give their children FAS (Fetal Alcohol Syndrome) • FAS is mental retardation, impaired motor skills, attention, memory, and language. • slow physical growth • facial abnormalities: widely spaced eyes, short eyelid openings, small upturned nose, thin upper lip, small head (brain not fully developed) • FAE (Fetal Alcohol Effects) - babies get this from mothers who generally drank in smaller quantities. • displays only some abnormalities • paternal alcohol use can also affect the baby • about 25% of Canadian mothers report to have drank alcohol sometime during their pregnancy • Radiation: •bombings in World War 2 •1986 Chernobyl, Ukraine •childhood cancer, smaller head size, physical deformities, and miscarriage • Environmental Pollution: •75,000 chemicals are in common use. •pregnant woman are not advised to eat predatory fish like swordfish, tuna, and shark which may have forms of mercury in them •another teratogen is lead • Infectious Disease: •parents having measles, chicken pox, mumps, etc can affect the baby •in the mid 1960ʼs there was an outbreak of rubella and it affected more than 20,000 North American babies. • eye cataracts, heart disease, genital, urinary, and intestinal •HIV/AIDS - HIV leads to AIDS • destroys the immune system • infected mostly women around the world especially in developing countries • most infants get it at the age of 6 months and only survive for the next 5-8 months • antiviral drug called zidovudine (
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