Growth, Development, and Aging Chapter 22 Copyright © 2016 by Elsevier Inc. All rights reserved.

Copyright © 2016 by Elsevier Inc. All rights reserved. Learning Objectives Discuss the concept of development as a biological process characterized by continuous modification and change. Discuss the major developmental changes characteristic of the prenatal stage of life from fertilization to birth. Discuss the three stages of labor that characterize a normal vaginal birth Copyright © 2016 by Elsevier Inc. All rights reserved.

Copyright © 2016 by Elsevier Inc. All rights reserved. Learning Objectives Identify the three primary germ layers and several derivatives in the adult body that develop from each layer. List and discuss the major developmental changes characteristic of the four postnatal periods of life. Discuss effects of aging on the major organ systems. Copyright © 2016 by Elsevier Inc. All rights reserved.

Development as a Biological Process Day of birth marks the end of prenatal period and beginning of postnatal period Our bodies are constantly changing; it’s an ongoing and continuous process It is important to remember, however, that life is not a series of stop-and-start events or individual and isolated periods of time. Copyright © 2016 by Elsevier Inc. All rights reserved.

Copyright © 2016 by Elsevier Inc. All rights reserved. Prenatal Period Prenatal period begins at conception and continues until birth (about 39 weeks) Science of fetal growth and development called embryology Embryology is s story of biological marvels that describes how a single microscopic cell transforms into a human being. Copyright © 2016 by Elsevier Inc. All rights reserved.

Copyright © 2016 by Elsevier Inc. All rights reserved. Prenatal Period Fertilization to implantation Requires ~10 days 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 Continued cell divisions of the morula produce a hollow ball of cells called a blastocyst Recall from Chapter 21 that each uterine tube extends outward from the uterus for about 10 centimeters. Copyright © 2016 by Elsevier Inc. All rights reserved.

Copyright © 2016 by Elsevier Inc. All rights reserved. Prenatal Period Fertilization to implantation 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 One of the specializations of the ovum is its incredible store of nutrients that help support this embryonic development until implantation has occurred. Copyright © 2016 by Elsevier Inc. All rights reserved.

Implantation and Early Development Amniotic cavity and placenta As blastocyst develops, it forms a structure with yolk sac and amniotic cavity Figure 22-4 shows implantation and early development. Copyright © 2016 by Elsevier Inc. All rights reserved.

Copyright © 2016 by Elsevier Inc. All rights reserved. Prenatal Period Periods of development Length of pregnancy, or gestation period, is about 39 weeks Embryonic phase extends from the third week after fertilization to the end of week 8 of gestation Fetal phase extends from week 8 to week 39 of gestation All organ systems are formed and functioning by month 4 of gestation The amniotic cavity becomes a fluid-filled, shock-absorbing sac, sometimes called a bag of waters. Placenta is composed of tissues from mother and child. Copyright © 2016 by Elsevier Inc. All rights reserved.

Human Embryos and Fetuses Figure 22-6 shows human embryos and fetuses at 35 days (A), 49 days (B), end of first trimester (C), and at 4 months (D). Copyright © 2016 by Elsevier Inc. All rights reserved.

Copyright © 2016 by Elsevier Inc. All rights reserved. Prenatal Period Formation of the primary germ layers Stem cells Unspecialized cells that reproduce to form specific lines of specialized cells Three primary germ layers appear in the developing embryo after implantation of the blastocyst Endoderm Inside layer Ectoderm Outside layer Mesoderm Middle layer Adult stem cells remain after early development but can only produce a few specialized kinds of cells in a particular tissue. Each germ layer gives rise to definite structures such as skin, nervous tissue, muscles, or digestive organs. Copyright © 2016 by Elsevier Inc. All rights reserved.

Primary Germ Layer Derivatives Table 22-1 shows the primary germ layer derivatives and the structures derived from each. Copyright © 2016 by Elsevier Inc. All rights reserved.

Copyright © 2016 by Elsevier Inc. All rights reserved. Prenatal Period Histogenesis and organogenesis Formation of new organs (organogenesis) and tissues (histogenesis) 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 Human development begins when two sex cells unite to form a single-celled zygote. Development of structure and function go hand in hand. Copyright © 2016 by Elsevier Inc. All rights reserved.

Copyright © 2016 by Elsevier Inc. All rights reserved. Prenatal Period Birth defects Any structural or functional abnormality present at birth May be caused by genetic factors Abnormal genes Abnormal number of chromosomes May be caused by environmental factors Environmental factors are called teratogens Include radiation, chemicals, and infections Especially harmful during the first trimester Nutritional deficiencies during pregnancy can also lead to birth defects. Copyright © 2016 by Elsevier Inc. All rights reserved.

Critical Periods of Neonatal Development Figure 22-7: The red areas show when teratogens are most likely to cause major birth defects, and the yellow areas show when minor defects are more likely to arise. Numbers refer to weeks of gestation. Copyright © 2016 by Elsevier Inc. All rights reserved.

Copyright © 2016 by Elsevier Inc. All rights reserved. Birth Parturition: Process of birth 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 A breech birth is one in which the fetus fails to turn head downward. This condition typically requires the baby to be born via cesarean section (C-section). Copyright © 2016 by Elsevier Inc. All rights reserved.

Copyright © 2016 by Elsevier Inc. All rights reserved. Stages of Labor Stage 1 Period from onset of uterine contractions until dilation of the cervix is complete Stage 2 Period from the time of maximal cervical dilation until the baby exits through the vagina Stage 3 Process of expulsion of the placenta through the vagina Labor is the process that results in the birth of a baby. To assess the general condition of a newborn, a system that scores five health criteria is used and is called an Apgar score (highest score is 10). Copyright © 2016 by Elsevier Inc. All rights reserved.

Copyright © 2016 by Elsevier Inc. All rights reserved. Postnatal Period Growth, development, and aging 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 Divisions of postnatal period Infancy Childhood Adolescence Adulthood Older adulthood Gradual changes in the physical appearance of the body as a whole and in the relative proportions of the head, trunk, and limbs are quite noticeable between birth and adolescence. Copyright © 2016 by Elsevier Inc. All rights reserved.

Changes in Proportions Figure 22-9: Notice the dramatic differences in head proportion. Courtesy Barbara Cousins. Copyright © 2016 by Elsevier Inc. All rights reserved.

Copyright © 2016 by Elsevier Inc. All rights reserved. Postnatal Period 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 (in respect to respiration and circulation) In neonatal period, the baby is referred to as the neonate. Copyright © 2016 by Elsevier Inc. All rights reserved.

Copyright © 2016 by Elsevier Inc. All rights reserved. Postnatal Period 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 Respiratory changes at birth include a deep and forceful first breath. Copyright © 2016 by Elsevier Inc. All rights reserved.

The Neonate Infant Figure 22-10 shows the neonate infant. Courtesy Marjorie M Pyle for Lifecircle, Costa Mesa, CA. Copyright © 2016 by Elsevier Inc. All rights reserved.

Spinal Curvatures Figure 22-11 shows the normal rounded curvature of the vertebral column in an infant (A) and the normal vertebral curvature in a toddler (B). A: From Hockenberry MJ, Wilson D: Wong’s essentials of pediatric nursing, ed 8, St Louis, 2009, Mosby. B: Copyright Kevin Patton, Lion Den, Inc., Weldon Spring, MO. Copyright © 2016 by Elsevier Inc. All rights reserved.

Copyright © 2016 by Elsevier Inc. All rights reserved. Postnatal Period Childhood Extends from end of infancy to sexual maturity or puberty – 12 to 14 years in girls and 14 to 16 years in boys By age 6, child appears more like a preadolescent than an infant or toddler By age 10, child has developed numerous motor and coordination skills The deciduous teeth, which began to appear at about 6 months of age, are lost during childhood, beginning at about 6 years of age. The permanent teeth, with the exception of wisdom teeth, all erupt by age 14. Copyright © 2016 by Elsevier Inc. All rights reserved.

Copyright © 2016 by Elsevier Inc. All rights reserved. Postnatal Period Adolescence Average age range varies; usually from 13−19 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 ~10 and boys at ~12 Growth plates fully close in adult; other structures such as the sinuses assume adult placement Adulthood Characterized by maintenance of existing body tissues Breast development is often the first sign of approaching puberty in girls, beginning about age 10. Most girls begin to menstruate at 12 to 13 years of age. In girls, the spurt in height begins between 10 and 12 and is complete by 14 or 15; in boys, the spurt begins between 12 and 13 and is generally complete by 16. Degeneration of body tissue begins in adulthood. Copyright © 2016 by Elsevier Inc. All rights reserved.

Copyright © 2016 by Elsevier Inc. All rights reserved. Growth in Height Figure 22-12 shows typical patterns of height gains until adulthood for boys and girls. From Mahan LK, Escott-Stump S: Krause’s food, nutrition, and diet therapy, ed 11, St Louis, 2004, Elsevier. Copyright © 2016 by Elsevier Inc. All rights reserved.

Copyright © 2016 by Elsevier Inc. All rights reserved. Postnatal Period Older adulthood Degenerative changes characterize older adulthood (also called senescence) Every organ system of the body undergoes degenerative changes Senescence culminates in death The study of aging is called gerontology. Copyright © 2016 by Elsevier Inc. All rights reserved.

Biological Changes Associated with Aging Figure 22-13 shows some biological changes associated with maturity and aging. Copyright © 2016 by Elsevier Inc. All rights reserved.

Copyright © 2016 by Elsevier Inc. All rights reserved. Effects of Aging Integumentary system With age, “sags” and becomes thin, dry, wrinkled Pigmentation problems are common Frequently thinning or loss of hair occurs 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 Physical activity can reduce loss of bone mass and mobility Older bones develop indistinct and shaggy-appearing margins with spurs (called lipping). Loss of bone mass and reduced mobility can be avoided or reduced by physical activity coupled with good nutrition. Copyright © 2016 by Elsevier Inc. All rights reserved.

Copyright © 2016 by Elsevier Inc. All rights reserved. Effects of Aging Central nervous system Advancing age: Increased risk of dementia Most have intact memories and have developed mature ability to reason and make decisions Some elderly individuals suffer from depression Dementia is the loss of memory and other functions of conscious thinking. Copyright © 2016 by Elsevier Inc. All rights reserved.

Copyright © 2016 by Elsevier Inc. All rights reserved. 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”) Loss of transparency of lens or cornea is common (cataract) Glaucoma (increase in pressure in eyeball) is often the cause of blindness in older adulthood Increased risk of retinal degeneration or detachment Increased need for bifocals to assist in accommodating near and distant vision. Copyright © 2016 by Elsevier Inc. All rights reserved.

Copyright © 2016 by Elsevier Inc. All rights reserved. Effects of Aging Special senses 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 Some degree of hearing impairment is universally present in the aged Smell and taste may be reduced; only about 40% of the taste buds present at age 30 remain at age 75 Loss of appetite may be caused partly by the replacement of taste buds with connective tissue cells. Copyright © 2016 by Elsevier Inc. All rights reserved.

Copyright © 2016 by Elsevier Inc. All rights reserved. Effects of Aging 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 With advancing years, a generalized atrophy or wasting of muscle tissue takes place as contractile muscle cells are replaced by connective tissue. Copyright © 2016 by Elsevier Inc. All rights reserved.

Copyright © 2016 by Elsevier Inc. All rights reserved. Effects of Aging Respiratory system Calcification of costal cartilages causes rib cage to remain in expanded position Wasting of respiratory muscles decreases respiratory efficiency Respiratory membrane thickens; movement of oxygen from alveoli to blood is slowed When the rib cage remains in a more expanded position, respiratory efficiency decreases, and a condition called barrel chest results. Copyright © 2016 by Elsevier Inc. All rights reserved.

Copyright © 2016 by Elsevier Inc. All rights reserved. Effects of Aging Urinary system Nephron units decrease in number by 50% between ages 30 and 75 Blood flow to kidney decreases and therefore ability to form urine decreases Bladder problems such as inability to void completely are caused by muscle wasting in the bladder wall Muscle atrophy in the bladder results in decreased capacity and inability to empty or void completely. Copyright © 2016 by Elsevier Inc. All rights reserved.