Transcript Document

Chapter 21
Growth and Development
Prenatal Period
 Prenatal period begins at conception and continues until birth
(about 39 weeks)
 Science of fetal growth and development called embryology
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
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
Prenatal Period
 Periods 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 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
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
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
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
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
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
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
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)
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
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
Postnatal Period
 Divisions of postnatal period
 Infancy
 Childhood
 Adolescence and adulthood
 Older adulthood
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
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
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
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
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
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
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
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
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
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
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
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 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