1. Growth and Development Chapter 21

2. Prenatal Period Prenatal period begins at conception and continues until birth (about 39 weeks) Science of fetal growth and development called embryology

3. Prenatal Period Fertilization to implantation requires about 10 days Fertilization normally occurs in outer third of oviduct Fertilized ovum called a zygote; zygote is genetically complete—all that is needed for expression of hereditary traits is time and nourishment After 3 days of cell division, the zygote has developed into a solid cell mass called a morula

4. Prenatal Period Continued cell divisions of the morula produce a hollow ball of cells called a blastocyst Blastocyst implants in the uterine wall about 10 days after fertilization Blastocyst forms the amniotic cavity and chorion of the placenta Placenta provides for exchange of nutrients between the mother and fetus

5. Prenatal Period Periods of development Length of pregnancy or gestation period is about 39 weeks Embryonic phase extends from 3 rd week after fertilization to the end of week 8 of gestation Fetal phase extends from week 8 to week 39 of gestation

6. Prenatal Period Three primary germ layers appear in the developing embryo after implantation of the blastocyst Endoderm—inside layer Ectoderm—outside layer Mesoderm—middle layer All organ systems are formed and functioning by month 4 of gestation

7. Prenatal Period Histogenesis and organogenesis Formation of new organs and tissues occurs from specific development of the primary germ layers Growth processes include cell differentiation, multiplication, growth, and rearrangement From 4 months of gestation until delivery, the development of the baby is mainly a matter of growth

8. Birth or Parturition Process of birth called parturition At the end of week 39 of gestation, the uterus becomes “irritable” Fetus takes head-down position against the cervix Muscular contractions begin, and labor is initiated Amniotic sac (“bag of waters”) ruptures Cervix dilates Fetus moves through vagina to exterior

9. Birth or Parturition Stages of labor Stage one—period from onset of uterine contractions until dilation of the cervix is complete Stage two—period from the time of maximal cervical dilation until the baby exits through the vagina Stage three—process of expulsion of the placenta through the vagina

10. Birth or Parturition Clinicians sometimes refer to the recovery period immediately following delivery of the placenta as the fourth stage of labor Cesarean section (C-section)—surgical delivery, usually through an incision in the abdomen and uterine wall

11. Birth or Parturition Multiple births—two or more infants from the same pregnancy Identical siblings result from the splitting of tissue from the same zygote, making them genetically identical Fraternal siblings develop from different ova that are fertilized separately

12. Disorders of Pregnancy Implantation disorders Ectopic pregnancy—implantation outside the uterus (for example, tubal pregnancy) Placenta previa—growth of the placenta at or near cervical opening, often resulting in separation of the placenta from the uterine wall Abruptio placentae—separation of a normally-placed placenta from the uterine wall Preeclampsia (toxemia of pregnancy)—syndrome of pregnancy that includes hypertension, proteinuria, and edema; may progress to eclampsia, a severe toxemia that may result in death

13. Disorders of Pregnancy Fetal death Spontaneous abortion (miscarriage)—loss before week 20 (or 500 g) Stillbirth—loss after 20 weeks Birth defects May be inherited (congenital abnormalities) or acquired Acquired defects are caused by teratogens (agents that disrupt normal development)

14. Disorders of Pregnancy Postpartum disorders Puerperal fever is caused by bacterial infection that may progress to septicemia and death; occurs in mothers after delivery (postpartum) Lactation and thus infant nutrition can be disrupted by anemia, malnutrition, and other factors Mastitis—inflammation or infection of the breast Milk can be supplied by another nursing mother or by breast milk substitutes Lactose intolerance results from an infant’s inability to digest lactose present in human or animal milk

15. Postnatal Period Postnatal period begins at birth and lasts until death Divisions of postnatal period into isolated time frames can be misleading; life is a continuous process; growth and development are continuous Obvious changes in the physical appearance of the body—in whole and in proportion—occur between birth and maturity

16. Postnatal Period Divisions of postnatal period Infancy Childhood Adolescence and adulthood Older adulthood

17. Infancy First 4 weeks called neonatal period Neonatology—medical and nursing specialty concerned with the diagnosis and treatment of disorders of the newborn Many cardiovascular changes occur at the time of birth fetus is totally dependent on mother, whereas the newborn must immediately become totally self-supporting (respiration and circulation) Respiratory changes at birth include a deep and forceful first breath

18. Infancy Developmental changes between the neonatal period and 18 months include: Doubling of birth weight by 4 months and tripling by 1 year 50% increase in body length by 12 months Development of normal spinal curvature by 15 months Ability to raise head by 3 months Ability to crawl by 10 months Ability to stand alone by 12 months Ability to run by 18 months

19. Childhood Extends from end of infancy to puberty—13 years in girls and 15 in boys Overall rate of growth remains rapid but decelerates Continuing development of motor and coordination skills Loss of deciduous or baby teeth and eruption of permanent teeth

20. Adolescence Average age range of adolescence is from 13 to 19 years Period of rapid growth resulting in sexual maturity (adolescence) Appearance of secondary sex characteristics regulated by secretion of sex hormones Growth spurt typical of adolescence; begins in girls at about 10 and in boys at about 12

21. Adulthood Growth plates fully close in adult; other structures such as the sinuses acquire adult placement Adulthood characterized by maintenance of existing body tissues Degeneration of body tissue begins in adulthood

22. Older adulthood Degenerative changes characterize older adulthood or senescence Every organ system of the body undergoes degenerative changes A variety of mechanisms of aging have been described The free-radical theory of aging states that the number of oxygen free radicals increases as one ages, thus increasing the rate of cellular damage Senescence culminates in death

23. Effects of Aging Skeletal system Aging causes changes in the texture, calcification, and shape of bones Bone spurs develop around joints Bones become porous and fracture easily Degenerative joint diseases such as osteoarthritis are common

24. Effects of Aging Integumentary system (skin) With age, skin “sags” and becomes: Thin Dry Wrinkled Pigmentation problems are common Frequent thinning or loss of hair occurs

25. Effects of Aging Urinary system Nephron units decrease in number by 50% between ages 30 and 75 Blood flow to kidney, and therefore ability to form urine, decreases Bladder problems such as inability to void completely are caused by muscle wasting in the bladder wall

26. Effects of Aging Respiratory system Calcification of costal cartilages causes rib cage to remain in expanded position, resulting in barrel chest Wasting of respiratory muscles decreases respiratory efficiency Respiratory membrane thickens; movement of oxygen from alveoli to blood is slowed

27. Effects of Aging Circulatory (cardiovascular) system Degenerative heart and blood vessel disease is among the most common and serious effects of aging Fat deposits in blood vessels (atherosclerosis) decrease blood flow to the heart and may cause complete blockage of the coronary arteries Hardening of arteries (arteriosclerosis) may result in rupture of blood vessels, especially in the brain (stroke) Hypertension or high blood pressure is common in older adulthood

28. Effects of Aging: Special senses All sense organs show a gradual decline in performance with age Eye lenses become hard and cannot accommodate for near vision; result is farsightedness in many people by age 45 (presbyopia or “old eye”) Glaucoma (increase in pressure in eyeball) is often the cause of blindness in older adulthood Loss of hair cells in inner ear produces frequency deafness in many older people Decreased transmission of sound waves caused by loss of elasticity of eardrum and fixing of the bony ear ossicles is common in older adulthood Only about 40% of the taste buds present at age 30 remain at age 75

29. Effects of Aging Reproductive system Changes in the sexual response Men—erection is more difficult to achieve and maintain; urgency for sex may decline Women—lubrication during intercourse may decrease Changes in fertility Men—may continue to be fertile throughout later adult years Women—experience menopause (cessation of reproductive cycling) between ages 45 and 60