Growth and Development

Chapter 21

Prenatal PeriodPrenatal period begins at conception and

continues until birth (about 39 weeks)Science of fetal growth and development

called embryology

Prenatal PeriodFertilization to implantation requires about 10

daysFertilization 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

Prenatal PeriodContinued cell divisions of the morula produce a

hollow ball of cells called a blastocystBlastocyst implants in the uterine wall about 10

days after fertilizationBlastocyst forms the amniotic cavity and

chorion of the placenta Placenta provides for exchange of nutrients

between the mother and fetus

Prenatal PeriodPeriods of development

Length of pregnancy or gestation period is about 39 weeks

Embryonic phase extends from 3rd week after fertilization to the end of week 8 of gestation

Fetal phase extends from week 8 to week 39 of gestation

Prenatal PeriodThree primary germ layers appear in the

developing embryo after implantation of the blastocystEndoderm—inside layerEctoderm—outside layerMesoderm—middle layer

All organ systems are formed and functioning by month 4 of gestation

Prenatal PeriodHistogenesis 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

Birth or ParturitionProcess 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”) rupturesCervix dilatesFetus moves through vagina to exterior

Birth or ParturitionStages 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

Birth or ParturitionClinicians 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

Birth or ParturitionMultiple births—two or more infants from the

same pregnancyIdentical 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

Disorders of PregnancyImplantation 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

Disorders of PregnancyFetal death

Spontaneous abortion (miscarriage)—loss before week 20 (or 500 g)

Stillbirth—loss after 20 weeksBirth defects

May be inherited (congenital abnormalities) or acquired

Acquired defects are caused by teratogens (agents that disrupt normal development)

Disorders of PregnancyPostpartum 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 factorsMastitis—inflammation or infection of the breastMilk can be supplied by another nursing mother or by

breast milk substitutesLactose intolerance results from an infant’s inability to

digest lactose present in human or animal milk

Postnatal PeriodPostnatal period begins at birth and lasts until

deathDivisions 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

Postnatal PeriodDivisions of postnatal period

InfancyChildhoodAdolescence and adulthoodOlder adulthood

InfancyFirst 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

InfancyDevelopmental changes between the neonatal

period and 18 months include:Doubling of birth weight by 4 months and

tripling by 1 year50% increase in body length by 12 monthsDevelopment of normal spinal curvature by 15

months Ability to raise head by 3 monthsAbility to crawl by 10 monthsAbility to stand alone by 12 monthsAbility to run by 18 months

ChildhoodExtends from end of infancy to puberty—13

years in girls and 15 in boysOverall rate of growth remains rapid but

deceleratesContinuing development of motor and

coordination skillsLoss of deciduous or baby teeth and eruption

of permanent teeth

AdolescenceAverage age range of adolescence is from 13

to 19 yearsPeriod of rapid growth resulting in sexual

maturity (adolescence)Appearance of secondary sex characteristics

regulated by secretion of sex hormonesGrowth spurt typical of adolescence; begins in

girls at about 10 and in boys at about 12

AdulthoodGrowth 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

Older adulthoodDegenerative changes characterize older

adulthood or senescenceEvery organ system of the body undergoes

degenerative changesA variety of mechanisms of aging have been

describedThe 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

Effects of AgingSkeletal system

Aging causes changes in the texture, calcification, and shape of bones

Bone spurs develop around jointsBones become porous and fracture easilyDegenerative joint diseases such as

osteoarthritis are common

Effects of AgingIntegumentary system (skin)

With age, skin “sags” and becomes:ThinDryWrinkled

Pigmentation problems are commonFrequent thinning or loss of hair occurs

Effects of AgingUrinary 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

Effects of AgingRespiratory 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

Effects of Aging

Circulatory (cardiovascular) systemDegenerative 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

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

Effects of AgingReproductive system

Changes in the sexual responseMen—erection is more difficult to achieve and maintain;

urgency for sex may declineWomen—lubrication during intercourse may decrease

Changes in fertilityMen—may continue to be fertile throughout later adult

yearsWomen—experience menopause (cessation of reproductive

cycling) between ages 45 and 60