1. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 1 Chapter 33 Growth and Development

2. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 2 Introduction  Prenatal period—period beginning with conception and ending at birth  Postnatal period—period beginning with birth and continuing until death  Human developmental biology—study of changes occurring during the cycles of life from conception to death

3. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 3 A New Human Life  Production of sex cells—spermatozoa are produced by spermatogenesis; ova are produced by oogenesis  Meiosis (Figures 33-1 and 33-2) Special form of cell division that reduces the number of chromosomes in each daughter cell to one half of those in the parent cell Special form of cell division that reduces the number of chromosomes in each daughter cell to one half of those in the parent cell Mature ova and sperm contain only 23 chromosomes, half as many as other human cells Mature ova and sperm contain only 23 chromosomes, half as many as other human cells Meiotic division—two cell divisions that occur one after another in succession Meiotic division—two cell divisions that occur one after another in succession  Meiotic division I and meiotic division II  Both divisions made up of an interphase, prophase, metaphase, anaphase, and telophase During prophase I of meiosis, “cross over” occurs where genetic material is “shuffled” During prophase I of meiosis, “cross over” occurs where genetic material is “shuffled” Daughter cells formed by meiotic division I contain a haploid number of chromosomes Daughter cells formed by meiotic division I contain a haploid number of chromosomes Meiotic division II—essentially the same as mitotic division; reproduces each of the two cells formed by meiotic division I and forms four cells, each with the haploid number of chromosomes Meiotic division II—essentially the same as mitotic division; reproduces each of the two cells formed by meiotic division I and forms four cells, each with the haploid number of chromosomes

4. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 4 A New Human Life  Production of sex cells (cont.)  Spermatogenesis (Figure 33-3)—process by which primitive male sex cells become transformed into mature sperm; begins approximately at puberty and continues throughout a man’s life Meiotic division I—one primary spermatocyte forms two secondary spermatocytes, each with 23 chromosomes Meiotic division I—one primary spermatocyte forms two secondary spermatocytes, each with 23 chromosomes Meiotic division II—each of the two secondary spermatocytes form a total of four spermatids Meiotic division II—each of the two secondary spermatocytes form a total of four spermatids

5. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 5 A New Human Life  Production of sex cells (cont.)  Oogenesis (Figure 33-4)—process by which primitive female sex cells become transformed into mature ova Mitosis—oogonia reproduce to form primary oocytes; most primary oocytes begin meiosis and develop to prophase I before birth; there they stay until puberty Mitosis—oogonia reproduce to form primary oocytes; most primary oocytes begin meiosis and develop to prophase I before birth; there they stay until puberty Once during each menstrual cycle, a few primary oocytes resume meiosis and migrate toward the surface of the ovary; usually only one oocyte matures enough for ovulation, and meiosis again halts at metaphase II Once during each menstrual cycle, a few primary oocytes resume meiosis and migrate toward the surface of the ovary; usually only one oocyte matures enough for ovulation, and meiosis again halts at metaphase II Meiosis resumes only if the head of a sperm cell enters the ovum Meiosis resumes only if the head of a sperm cell enters the ovum

6. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 6 A New Human Life  Ovulation and insemination  Ovulation—expulsion of the mature ovum from the mature ovarian follicle, into the abdominopelvic cavity, and then the uterine (fallopian) tube  Insemination—expulsion of seminal fluid from male into the female vagina; sperm travel through cervix and uterus and into uterine (fallopian) tubes

7. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 7 A New Human Life  Fertilization—also known as conception (Figure 33-5)  Most often occurs in the outer one third of oviduct  Ovum attracts and “traps” sperm with special receptor molecules on its surface  When one spermatozoon enters ovum, ovum stops collecting sperm on its surface  The sperm releases its nuclear chromosomes into the ovum; proteins and RNA from the sperm enter the ovum to assist with early development  23 chromosomes from the sperm head and 23 chromosomes in the ovum comprise a total of 46 chromosomes  Zygote—fertilized ovum; genetically complete

8. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 8 Prenatal Period  Begins with conception and continues until the birth of a child  Cleavage and implantation (Figure 33-6)—once zygote is formed, it immediately begins to divide  Morula—solid mass of cells formed from zygote; takes approximately 3 days; continues to divide (Figure 33-7)  Blastocyst—by the time developing embryo reaches uterus, it has formed a hollow ball of cells, which implants into uterine lining (Figure 33-8)  Approximately 10 days pass from fertilization until implantation in uterine lining; ovum has a store of nutrients that support this embryonic development until implantation has occurred  Blastocyst has an outer layer of cells and an inner cell mass Trophoblast—outer wall of blastocyst Trophoblast—outer wall of blastocyst Inner cell mass—as blastocyst develops, yolk sac and amniotic cavity are formed (Figure 33-9) Inner cell mass—as blastocyst develops, yolk sac and amniotic cavity are formed (Figure 33-9)  In humans, yolk sac’s functions are largely nonnutritive  Amniotic cavity becomes a fluid-filled, shock-absorbing sac (bag of waters) in which embryo floats during development (Figure 33-10) Chorion develops from trophoblast to become an important fetal membrane in the placenta Chorion develops from trophoblast to become an important fetal membrane in the placenta

9. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 9 Prenatal Period  Cleavage and implantation (cont.)  Placenta (Figure 33-11) Anchors fetus to uterus and provides “bridge” for exchange of nutrients and waste products between mother and baby Anchors fetus to uterus and provides “bridge” for exchange of nutrients and waste products between mother and baby Also serves as excretory, respiratory, and endocrine organ Also serves as excretory, respiratory, and endocrine organ Placental tissue normally separates maternal and fetal blood supplies Placental tissue normally separates maternal and fetal blood supplies Has important endocrine functions—secretes large amounts of human chorionic gonadotropin (HCG), which stimulates the corpus luteum to continue its secretion of estrogen and progesterone (Figure 33-12) Has important endocrine functions—secretes large amounts of human chorionic gonadotropin (HCG), which stimulates the corpus luteum to continue its secretion of estrogen and progesterone (Figure 33-12)

10. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 10 Prenatal Period  Periods of development (Figures 33-13 through 33-15)  Gestation period—approximately 39 weeks; divided into three 3-month segments called trimesters  Embryonic phase extends from fertilization until the end of week 8 of gestation  Fetal phase—weeks 8 to 39

11. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 11 Prenatal Period  Formation of the primary germ layers  Three layers of specialized cells develop early in first trimester of pregnancy  Cells of embryonic disk differentiate and form each of the three primary germ layers  Each primary germ layer gives rise to specific organs and systems of the body (Figure 33-16)  There are three primary germ layers: Endoderm—inside layer Endoderm—inside layer Ectoderm—outside layer Ectoderm—outside layer Mesoderm—middle layer Mesoderm—middle layer

12. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 12 Prenatal Period  Histogenesis and organogenesis (Figure 33-19)  Histogenesis—process by which primary germ layers develop into different kinds of tissues  Organogenesis—how tissues arrange themselves into organs  Differentiation and development of the reproductive systems are an example Reproductive tract (Figure 33-17) Reproductive tract (Figure 33-17)  Gonads attach to mesonephric (Wolffian) ducts, which become the male reproductive tract  Gonads (unattached) and paramesonephric (Müllerian) ducts develop into the female reproductive tract External genitals (Figure 33-18) External genitals (Figure 33-18)  In the male, the genital tubercle eventually becomes the glans of the penis and the folds become the penis shaft and scrotum  In the female, the genital tubercle becomes the clitoris and the folds become the labia

13. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 13 Birth, or Parturition  Transition between prenatal and postnatal periods of life  Stages of labor (Figure 33-20)  Stage one—period from onset of uterine contractions until cervical dilation is complete  Stage two—period from maximal cervical dilation until the baby exits through the vagina  Stage three—process of expulsion of the placenta through the vagina

14. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 14 Birth, or Parturition  Multiple births—birth of two or more infants from the same pregnancy; twins are most common (Figure 33-21)  Identical twins result from the splitting of embryonic tissue from the same zygote early in development  Fraternal twins result from the fertilization of two different ova by two different spermatozoa

15. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 15 Postnatal Period  Begins at birth and continues until death; commonly divided into a number of periods (Figure 33-22)  Infancy begins at birth and lasts until approximately 18 months  Neonatal period—first 4 weeks of infancy; dramatic changes occur at a rapid rate (Figure 33-23)  Changes allow the infant to become totally self-supporting, especially respiratory and cardiovascular systems (Figure 33-24)

16. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 16 Postnatal Period  Childhood extends from end of infancy to sexual maturity, or puberty  Early childhood—growth continues at a rapid pace but slows down  By age 6, child looks more like a preadolescent than an infant or toddler  Nervous and muscular systems develop rapidly during middle years of childhood  Deciduous teeth are lost during childhood, beginning at approximately 6 years of age  Permanent teeth have erupted by age 14, except for third molars (wisdom teeth)

17. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 17 Postnatal Period  Adolescence and adulthood  Adolescence is considered to be the teenage years (from 13 to 19); marked by rapid and intense physical growth, resulting in sexual maturity Puberty—stage of adolescence during which a person becomes sexually mature Puberty—stage of adolescence during which a person becomes sexually mature Changes triggered by increases in reproductive hormones (Figure 33-25) Changes triggered by increases in reproductive hormones (Figure 33-25) Primary sexual characteristics—maturity of gonads and reproductive tract Primary sexual characteristics—maturity of gonads and reproductive tract Secondary sexual characteristics—fat and hair distribution, skeletal changes, etc. (Figure 33-26) Secondary sexual characteristics—fat and hair distribution, skeletal changes, etc. (Figure 33-26)  Adulthood—characterized by maintenance of existing body tissues

18. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 18 Postnatal Period  Older adulthood and senescence  As a person grows older, a gradual decline occurs in every major organ system in the body  Gerontologists theorize a number of different aging mechanisms, all of which may be involved in the processes of aging: Limit on cell reproduction Limit on cell reproduction Environmental factors Environmental factors Viruses Viruses Aging genes Aging genes Degeneration of mitochondria—perhaps progressive damage by oxygen free-radicals (Figure 33-27) Degeneration of mitochondria—perhaps progressive damage by oxygen free-radicals (Figure 33-27)

19. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 19 Effects of Aging—Common Degenerative Changes That Frequently Characterize Senescence (Figure 33-28)  Skeletal system (Figure 33-29)  Bones decrease in bone mineral density (BMD ) and thus change in texture, degree of calcification, and shape  Lipping occurs, which can limit range of motion  Decreased bone size and density lead to increased risk of fracture  Decreased BMD can be avoided (at least partly) by exercise and adequate calcium intake

20. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 20 Effects of Aging—Common Degenerative Changes That Frequently Characterize Senescence (Figure 33-28)  Muscular system (Figure 33-30)  Muscle mass decreases to about 90% by age 50 and around 50% by age 80  The number of muscle fibers decreases as humans age but can be offset by an increase in muscle fiber size through exercise  Ratio of “fast” to “slow” functioning in muscle fibers decreases, slowing the function of muscle organs

21. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 21 Effects of Aging—Common Degenerative Changes That Frequently Characterize Senescence (Figure 33-28)  Integumentary system (skin)  Skin becomes dry, thin, and inelastic  Pigmentation changes and thinning hair are common problems associated with aging

22. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 22 Effects of Aging—Common Degenerative Changes That Frequently Characterize Senescence (Figure 33-28)  Urinary system  Number of nephron units in the kidney decreases by almost 50% between the ages of 30 and 75  Decreased blood flow through kidneys reduces overall function and excretory capacity  Diminished muscle tone in bladder results in decreased capacity and inability to empty, or void, completely

23. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 23 Effects of Aging—Common Degenerative Changes That Frequently Characterize Senescence (Figure 33-28)  Respiratory system  Costal cartilages become calcified  Respiratory efficiency decreases  Decreased strength of respiratory muscles

24. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 24 Effects of Aging—Common Degenerative Changes That Frequently Characterize Senescence (Figure 33-28)  Cardiovascular system  Degenerative heart and blood vessel disease—one of the most common and serious effects of aging  Atherosclerosis—build-up of fatty deposits on blood vessel walls narrows the passageway for blood  Arteriosclerosis—“hardening” of the arteries  Hypertension—high blood pressure

25. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 25 Effects of Aging—Common Degenerative Changes That Frequently Characterize Senescence (Figure 33-28)  Special senses  Sense organs—gradual decline in performance and capacity with aging  Presbyopia—far-sightedness due to hardening of lens  Cataract—cloudy lens, which impairs vision  Glaucoma—increased pressure within the eyeball; if left untreated, often results in blindness  Decreased hearing  Decreased taste

26. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 26 Effects of Aging—Common Degenerative Changes That Frequently Characterize Senescence (Figure 33-28)  Reproductive systems  Mechanism of sexual response may change  Fertility decreases  In females, menopause occurs between ages of 45 and 60

27. Mosby items and derived items © 2007, 2003 by Mosby, Inc.Slide 27 Causes of Death  In developed countries such as the United States, heart disease, cancer, and stroke (CVA) are among the leading causes of death (Figure 33-31)  In developing countries, heart disease and stroke are also leading causes of death, along with infectious diseases such as HIV/AIDS, diarrheal disorders, and malaria