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Chapter 4. Prenatal Development and Birth. “There was a star danced and under that I was born.” William Shakespeare English Playwright, 17 th Century. Learning Goals. Describe prenatal development. Discuss the birth process. Explain the changes that take place in the postpartum period.

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Chapter 4


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    1. Chapter 4 Prenatal Development and Birth

    2. “There was a star danced and under that I was born.” • William Shakespeare English Playwright, 17th Century

    3. Learning Goals • Describe prenatal development. • Discuss the birth process. • Explain the changes that take place in the postpartum period.

    4. The Course of Prenatal Development • The Germinal Period • The Embryonic Period • The Fetal Period

    5. The Germinal Period • Occurs in the first 2 weeks after conception. • By about 1 week after conception, the zygote is composed of 100 to 150 cells. • Period includes the creation of the zygote, continued cell division, and attachment of the zygote to the uterine wall. • Implantation, or attachment to the uterine wall, occurs about 10 days after conception.

    6. The Differentiation of Cells • Blastocyst - the inner layer of cells that develops during the germinal period and later becomes the embryo • Trophoblast - the outer layer of cells that develops during the germinal period and later provides nutrition and support for the embryo

    7. The Embryonic Period • Occurs from 2 to 8 weeks after conception • The rate of cell differentiation intensifies, support systems for the cells form, and organs appear • The name of the mass of cells now changes from zygote to embryo

    8. Cell Layers of the Embryo • Endoderm - inner layer; develops into the digestive and respiratory systems • Ectoderm - outermost layer; becomes the nervous system, sensory receptors (ears, nose, eyes), and skin parts (hair and nails) • Mesoderm - middle layer; becomes the circulatory system, bones, muscles, excretory system, and reproductive system

    9. Prenatal Life-Support Systems • The Placenta - consists of a disk-shaped group of tissues in which small blood vessels from the mother and the offspring intertwine but do not join • The Umbilical Cord - contains two arteries and one vein, that connects the baby to the placenta • The Amnion - a bag or envelope that contains a clear fluid in which the developing embryo floats

    10. Important Embryonic Developments • Third Week - Neural tube develops • 21 Days - Eyes begin to appear • 24 Days - Heart cells begin to differentiate • Fourth Week - First appearance of the urogenital system, arm and leg buds appear, chambers of the heart take shape, blood vessels surface • Fifth to Eighth Week - Arms and legs differentiate further, face starts to form, intestinal tract develops, facial structures fuse • 8 Weeks - organisms weighs 1/30 ounce, 1 inch long

    11. Definition of Organogenesis • The process of organ formation that takes place during the first 2 months of prenatal development

    12. The Fetal Period The period that begins 2 months after conception and lasts, on average, 7 months Significant time periods: Three months after conception The end of the fourth month The end of the fifth month The end of the sixth month The end of the seventh month The eighth and ninth months

    13. Three Months after Conception • The fetus is 3 in. long and weighs 1 oz. • The fetus becomes active, moving its arms, legs, head, and opening and closing its mouth. • The face, forehead, eyelids, nose, chin, upper arms, lower arms, hands, and lower limbs are all distinguishable. • The genitals can be distinguished as male or female.

    14. The End of the Fourth Month • The fetus is 6 in. long and weighs 4-7 oz. • A growth spurt occurs in the body’s lower parts. • Prenatal reflexes are stronger. • Arm and leg movements can be felt by the mother for the first time.

    15. The End of the Fifth Month • The fetus is 12 in. long and weighs close to 1 lb. • Structures of skin have formed (such as toe and finger nails). • The fetus is more active, and shows a preference for a particular position in the womb.

    16. The End of the Sixth Month • The fetus is approximately 14 in. long and weighs about 2 lbs. • The eyes and eyelids are completely formed. • A fine layer of hair covers the head. • A grasping reflex is present. • Irregular breathing movements occur.

    17. The End of the Seventh Month • The fetus is 16 in. long and weighs 3 lbs. • The fetus is adding body fat. • The fetus is very active. • Basic breathing begins.

    18. The Eighth and Ninth Months • The fetus grows longer and gains substantial weight, about another 4 lbs. • Fatty tissues develop, and the functioning of organ systems, such as heart and kidneys, increases. • At birth, the average American baby is about 20 in. long and weighs 7 lbs.

    19. Teratology - The field of study that investigates the causes of birth defects. • Teratogen - Any agent that causes a birth defect. • Numerous teratogens exist, thus almost every fetus is exposed to at least some. • Specific teratogens do not usually cause a specific birth defect. • It may take a long time for the effects of a teratogen to show up. • Only about half of all potential effects appear at birth.

    20. Factors that influence the severity of the damage to an unborn child and the type of defect that occurs: • Dose – the greater the dose, the greater the effect. • Time of Exposure – Teratogens do more damage when they occur at some points in development rather than others. • Genetic Susceptibility – based upon genotype of pregnant mother and genotype of the fetus

    21. Prenatal Sensitivity to Teratogens • Sensitivity during Organogenesis • Sensitivity during the Fetal Period

    22. Sensitivity during Organogenesis • The probability of a structural defect is greatest during organogenesis. • 15 - 25 days after conception, the brain is most vulnerable. • 24 - 40 days after conception, the eyes are most vulnerable. • 20 - 40 days after conception, the heart is most vulnerable. • 24 - 36 days after conception, the legs are most vulnerable.

    23. Sensitivity during the Fetal Period • Exposure is less likely to cause anatomical defects. • Exposure is more likely to stunt growth. • Exposure is more likely to create problems in organ functioning.

    24. Prescription and Nonprescription Drugs Both can have possible effects on the fetus. A tragic example is with the tranquilizer thalidomide, prescribed in the early 1960s. Mothers do not have to be chronic drug users for the fetus to be harmed. Taking the wrong drug at the wrong time is enough to physically handicap offspring for life.

    25. Antibiotics (streptomycin, tetracycline) Some depressants Certain hormones (progestin, synthetic estrogen) Accutane Prescription Drugs that Can Function as Teratogens

    26. Diet Pills Aspirin Caffeine A small increase in the risks for spontaneous abortion and low birthweight occurs for pregnant women consuming >150 mg caffeine per day. No effects were found for pregnant women who drank decaffeinated coffee. FDA recommends either no caffeine or very little. Nonprescription Drugs that Can Function as Teratogens

    27. PsychoactiveDrugs Alcohol Nicotine Illegal Drugs

    28. Heavy Drinking Moderate Drinking Alcohol

    29. Fetal Alcohol Syndrome (FAS) - A cluster of abnormalities that appears in the offspring of mothers who drink alcohol heavily during pregnancy Facial deformities Defective limbs, face, and heart Below average intelligence, with some cases of mental retardation Adults with FAS found to have a high incidence of mental disorders, such as depression or anxiety Heavy Drinking during Pregnancy

    30. “Moderate” is defined as 1 to 2 drinks a day. Infants were less attentive and alert, with effects still present at 4 years of age. Study showed that prenatal alcohol exposure was a better predictor of adolescent alcohol use and its negative consequences than was family history of alcohol problems. Moderate Drinking during Pregnancy

    31. Fetal and neonatal deaths are higher among smoking mothers. There exists a higher incidence of preterm births and lower birthweights. Intervention programs designed to get pregnant women to stop smoking can reduce some of smoking’s negative effects, especially by raising birthweights. Nicotine

    32. The Research on Smoking during Pregnancy Studies have shown urine samples of newborns with smoking mothers had substantial amounts of one of the strongest carcinogens in tobacco smoke (NNK). Another study showed prenatal exposure to nicotine was related to poorer language and cognitive skills at 4 years of age. Respiratory problems and SIDS are more common among the offspring of mothers who smoked during pregnancy.

    33. Cocaine Marijuana Heroin Illegal Drugs

    34. Cocaine exposure during prenatal development is associated with reduced birthweight, length, and head circumference. Cocaine exposure has been associated with impaired motor development at 2 years of age. Fetal cocaine exposure is also linked with impaired information processing (poor attentional skills through 5 years of age; impaired processing of auditory information after birth). Cocaine Use during Pregnancy

    35. Research findings must be interpreted with caution due to the presence of other factors in the lives of pregnant women who use cocaine: Poverty Malnutrition Other substance abuse:cigarettes, marijuana, alcohol, amphetamines Other Related Influences

    36. Associated with increased tremors and startles among newborns Associated with poorer verbal and memory development at 4 years of age Marijuana Use during Pregnancy

    37. Young infants are addicted and show withdrawal symptoms characteristic of opiate abstinence: Tremors Irritability Abnormal crying Disturbed sleep Impaired motor control Behavioral problems are still present at 1 yr-old. Attention deficits may appear later in development. Heroin Use during Pregnancy

    38. EnvironmentalHazards Radiation: nuclear environments, X-rays, computer monitors Chemicals: carbon monoxide, mercury, lead, pesticides, PCBs Heat: saunas, hot tubs

    39. Can cause gene mutation Can cause chromosomal abnormalities X-rays can effect the developing embryo most during the first several weeks after conception. Findings on Radiation Exposure

    40. Early exposure to lead affects children’s mental development. Women who ate PCB-polluted fish were more likely to have smaller, preterm infants who reacted slowly to stimuli. Prenatal exposure to PCBs has also been associated with problems in visual discrimination and short-term memory in 4-year-old children. Findings on Hazardous Chemicals

    41. Prolonged exposure to heat in saunas or hot tubs that raises the mother’s body temperature creates a fever that endangers the fetus. The high temperature may interfere with cell division and may cause birth defects or even fetal death. Effects of Exposure to High Temperatures

    42. Infectious Diseases Nutrition Emotional States and Stress Maternal Age OtherMaternalFactors

    43. Rubella Syphilis Genital Herpes AIDS Infectious Diseases

    44. (or German Measles) Greatest damage occurs when contracted in the 3rd and 4th weeks of pregnancy, although infection during the 2nd month is also damaging. A rubella outbreak in the mid 1960s resulted in 30,000 prenatal and neonatal deaths. It also caused more than 20,000 infants to be affected, displaying mental retardation, blindness, deafness, and heart problems. Rubella

    45. Syphilis is a sexually transmitted disease. It is more damaging in later prenatal development, 4 months or more after conception. It damages organs after they are formed, including eye lesions (which can cause blindness) skin lesions If it is present at birth it can cause problems with the central nervous system and gastrointestinal tract. Syphilis

    46. Newborns contract the virus when they are delivered through the birth canal of a mother with genital herpes. One-third of babies delivered through an infected birth canal die. One-fourth of babies delivered through an infected birth canal become brain damaged. If an active case of genital herpes is detected close to a woman’s due date, a cesarean section can be performed to keep the newborn safe. Genital Herpes

    47. AIDS is a sexually transmitted disease which destroys the body’s immune system. A mother can infect her offspring in three ways: during gestation across the placenta during delivery through contact with maternal body fluids postpartum through breast feeding Babies born to infected mothers can be infected and symptomatic infected but asymptomatic (with the possibility of developing symptoms up until 15 months of age) not infected at all AIDS