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CHAPTER 18 DEVELOPMENT AND AGING BEHAVIORAL OBJECTIVES 1. Describe the process of fertilization, including where and how it occurs. [18.1, pp.364-365, Fig. 18.2] 2. Describe a woman’s symptoms indicating that she is pregnant, and explain the basis of the pregnancy test. [18.1, p.365] 3. Explain what development stages occur before implantation. [18.1, p. 365, Fig. 18.3] 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. State the four processes of development. [18.2, p.366] List the three embryonic germ layers and what each gives rise to. [18.2, p. 366, Fig. 18.4, Table 18.1] Explain the significance of the primitive streak and neurula. [18.2, pp. 366-367, Fig. 18.5] Name the extraembryonic membranes stating the function of each. [18.2, p.368, Fig. 18.6] Describe the structure and function of the placenta. [18.2, p.368] Trace the path of blood in the fetus and between the fetus and the placenta. [18.2, p.368-369, Fig. 18.7] Describe genetic testing of an embryo (amniocentesis). [Health Focus, pp.370-371, Fig. 18A] Describe the weekly events of embryonic development and the monthly events of fetal development. [18.2, p.372-374, Figs. 18.8-18.11] Explain how male and female sex organs develop. [18.3, pp. 374-375, Fig. 18.12] Describe the three stages of birth. [18.4, p.376, Fig. 18.13] Describe the anatomy of the breast, and give the names and functions of the hormones that affect the breast. [18.4, p.377, Fig. 18.14] Describe the fluids produced by the breasts following birth. [18.4, p.377] State three theories of aging. [18.45, p.378] Describe the effects of aging on body systems and ways to prevent a decline in body functions. [17.5, pp.379380, Fig. 18.16] Understand and use the bold-faced and italicized terms included in this chapter. [Understanding Key Terms, p.383] EXTENDED LECTURE OUTLINE 18.1 Fertilization Fertilization normally occurs in the upper third of the oviduct. Uterine and oviduct contractions may help transport the sperm. Fertilization occurs when a sperm and egg interact. The sperm must pass through the several layers of follicular cells surrounding the egg, called the corona radiata. The egg cell also has its own plasma membrane, a vitelline membrane, and the zona pellucida. Sperm gain entry through a species-specific mechanism of contacting the vitelline membrane, then fusing with the egg plasma membrane before the sperm nucleus enters the cell. Once the sperm and egg nuclei fuse, fertilization is accomplished, and a zygote forms. The zygote travels down the oviduct, begins to undergo cell divisions, and eventually implants in the endometrium. It then secretes human chorionic gonadotropin (HCG), the presence of which is the basis for pregnancy tests. Mader VRL CD-ROM Image 0347l.jpg (Fig. 18.1) Image 0348l.jpg (Fig. 18.2) Image 0349al.jpg (Fig. 18.3) Image 0349bl.jpg (Fig. 18.3) Dynamic Human 2.0 CD-ROM Reproductive/Explorations/Oogenesis Reproductive/Explorations/Spermatogenesis Mader ESP Modules Online Animals/Development/Fertilization 97 Case Studies Online The Case of the Embryos Without Parents Frozen Embryos Transparencies 263 (Fig. 18.2) 264 (Fig. 18.3) 18.2 Development Before Birth Processes of Development Embryonic development of humans and all other animals includes the following processes: Cleavage begins right after fertilization as the zygote divides and divides again. The size of the cell does not increase during this stage. Morphogenesis is the reshaping of the embryo as cells migrate to different areas. Differentiation occurs as cells take on specific structures and then functions. Growth accompanies cell division during embryonic development. Morula During cleavage, the mass of cells is referred to as a morula. Blastula The blastula stage begins once the morula transforms into a hollow ball with an inner cell mass off to one side. The inner cell mass becomes an embryonic disk composed of two germ layers: an upper ectoderm and a lower endoderm. Gastrula During gastrulation, the bilayered disk elongates, and a primitive streak is seen at the midline of the embryo. Some of the cells within the primitive streak invaginate, giving rise to a third germ layer, the mesoderm. As differentiation continues throughout development, the three germ layers give rise to all other tissues and organs of the body (see Table 18.1). Neurula Mesoderm cells along the main axis give rise to a notochord, which is eventually replaced by the vertebral column. Neural folds fuse to form a neural tube, which gives rise to the spinal cord and brain. During neurulation, induction occurs, a process in which one tissue influences the development of another. Induction probably requires the presence of certain chemicals that turn genes on. Somites arise from the mesoderm. These become the muscles of the body and the vertebrae. A body cavity called the coelom forms and is lined by mesoderm. The coelom becomes the thoracic and abdominal cavities. Extraembryonic Membranes Extraembryonic membranes extend out beyond the embryo. The amnion envelops the fetus in protective fluid. The yolk sac is the first site of red blood cell formation, and part of this membrane eventually becomes a portion of the umbilical cord. The allantois contributes to the circulatory system, and its vessels become the umbilical blood vessels. The chorion, the outermost membrane, contributes to the placenta. Fetal Circulation The chorion contributes the placenta on the fetal side, while uterine tissues supply the placenta on the maternal side. Fetal and maternal blood do not mix. Instead, carbon dioxide and wastes diffuse from the fetal side of the placenta, and oxygen and nutrients move from the maternal side to the fetal side. The umbilical cord carries gases and nutrients to the fetus from the placenta. Harmful molecules can cross the placenta; this is especially damaging during the embryonic period. 98 Path of Fetal Blood Fetal circulation is different from adult circulation because the fetus does not breathe air. Blood passes between the atria of the heart through an oval opening because not as much blood needs to travel to the lungs. An arterial duct shunts blood between the pulmonary trunk and aorta for the same reason. Two umbilical arteries lead to the placenta; one umbilical vein takes nutrients to the baby. The umbilical vein joins a venous duct entering the vena cava. The persistence of the oval opening at birth is the most common heart defect in newborns. Embryonic Development Embryonic development lasts from fertilization to the end of the second month of gestation, at which time all organ systems have formed. Fetal development occurs from the third through the ninth months of pregnancy. First Month The zygote undergoes the morula stage, and the blastocyst implants in the uterine lining by the end of the second week. The inner cell mass is present, and extraembryonic membranes are forming. The early embryonic cells are called stem cells and may be useful in curing certain diseases. At the end of the first month, organs are developed and the placenta is forming. Limb buds are present, and eyes, ears, and a nose appear. Second Month Legs, arms, and digits are better formed, the head is large, and all internal organs have appeared. During the first two months, the mother may experience nausea, breast tenderness, fatigue, and other symptoms. At the end of two months, the embryonic stage is over. Fetal Development Fetal development extends from the third to the ninth month. Third and Fourth Months During the third and fourth months, the body increases in size, and epidermal refinements (eyelashes, nipples) become apparent. Bone is replacing cartilage. During this time, it becomes possible to distinguish males from females. Fifth through Seventh Months The mother can feel fetal movement. The fetus’s thin skin is covered with lanugo, and the eyelids open fully. At the end of seven months, the fetus can survive if born prematurely. Its lungs may lack surfactant, however, putting the baby at risk. Eighth and Ninth Months During the last two months, the fetus grows greatly in size. It rotates its head down toward the cervix. Mader VRL CD-ROM Image 0350l.jpg (Fig. 18.4) Image 0351l.jpg (Fig. 18.5) Image 0352l.jpg (Fig. 18.6) Image 0353al.jpg (Fig. 18.7) Image 0353bl.jpg (Fig. 18.7) Image 0353cl.jpg (Fig. 18.7) Image 0353dl.jpg (Fig. 18.7) Image 0354al.jpg (Fig. 18A) Image 0354bl.jpg (Fig. 18B) Image 0354cl.jpg (Fig. 18C) Image 0355l.jpg (Fig. 18.8) Image 0356l.jpg (Fig. 18.9) Image 0357l.jpg (Fig. 18.10) Image 0358l.jpg (Fig. 18.11) 99 Dynamic Human 2.0 CD-ROM Reproductive/Explorations/Amniocentesis Life Science Animations VRL 2.0 Animal Biology/Reproduction and Development/ Human Development Before Implantation Animal Biology/Reproduction and Development/ Human Embryonic Development Mader ESP Modules Online Case Studies Online Animals/Development/Early Development Animals/Development/Human Development Animals/Development/Hormones and Pregnancy Development Artificial Womb Hormones and Multiple Births Transparencies 265 (Fig. 18.4) 266 (Fig. 18.5) 267 (Fig. 18.6) 268 (Fig. 18.7) 269 (Fig. 18A) 270 (Fig. 18.8) 18.3 Development of Male and Female Sex Organs Gonads begin developing during the seventh week of gestation. Genes on the Y chromosome code for testes development. In the absence of the Y chromosome, fetuses are female and develop a vagina, uterus, and ovaries. Males and females have somewhat analogous development during various fetal stages. Mader VRL CD-ROM Image 0359al.jpg (Fig. 18.12) Image 0359bl.jpg (Fig. 18.12) Image 0359cl.jpg (Fig. 18.12) Image 0359dl.jpg (Fig. 18.12) Image 0359el.jpg (Fig. 18.12) Image 0359fl.jpg (Fig. 18.12) Transparencies 271 (Fig. 18.12a) 272 (Fig. 18.12b) 18.4 Birth Estrogen, prostaglandins, and oxytocin cause the uterus to contact and expel the fetus. Stage 1 Stage 1 labor involves contractions that move the baby’s head downward, enhancing effacement and dilation of the cervix. The amnion breaks, releasing amniotic fluid. This stage ends when the cervix is completely dilated. Stage 2 Stage 2 labor has frequent contractions of longer duration. The mother experiences a desire to push. An episiotomy is often performed to prevent tearing. The baby is pushed out during this stage. Stage 3 Stage 3 is the delivery of the afterbirth. 100 Female Breast and Lactation No milk is produced during pregnancy, but milk ducts and alveoli proliferate during that time, and the breasts enlarge. Once the baby is delivered, the pituitary secretes prolactin, and milk is produced. Suckling of the baby at the breast enhances milk production. Mader VRL CD-ROM Image 0360l.jpg (Fig. 18.13) Image 0361l.jpg (Fig. 18.14) Dynamic Human 2.0 CD-ROM Reproductive/Histology/Mammary Gland Reproductive/Clinical Concepts/Breast Cancer Mader ESP Modules Online Case Studies Online Animals/Development/Hormones and Pregnancy Treatment of Critically Ill Newborns Should You Need a License to Be a Parent? Transparencies 273 (Fig. 18.13) 274 (Fig. 18.14) 18.5 Development After Birth Development is a lifelong process into adulthood. After that period, aging occurs. Gerontology is the study of aging. Theories of Aging Genetic in Origin One theory of aging suggests that aging has a genetic basis. Cells can divide only so many times. As we grow older, it may be that more cells age and die. Also, some cell lines may die before that maximum number of cell divisions has been reached. In addition, offspring of long-lived people also tend to be long-lived. Some people may have genes that code for efficient enzymes that remove free radicals, causing the individuals to live longer. Whole-Body Process A second theory of aging suggests that a hormonal decline can affect many different organ systems. The immune system no longer performs as well, which is perhaps why cancer is more prevalent in the elderly. Aging may be due to the failure of a particular tissue type found throughout the body. Extrinsic Factors A third theory on aging suggests that years of poor health habits contribute most to aging. Osteoporosis is a good example. Effect of Age on Body Systems Skin Skin loses elasticity and becomes thinner with age, resulting in sagging and wrinkling. Fewer sweat glands are present, so temperature regulation is less efficient. Processing and Transporting Deterioration of the cardiovascular system is the leading cause of death among the elderly. The heart shrinks with age, and fatty deposits clog arteries. Low-cholesterol, low-fat diets slow degenerative changes. Lungs lose some elasticity, so ventilation is reduced. A reduced blood supply to the kidneys results in the kidneys becoming smaller and less efficient. The digestive tract may lose muscle tone but still absorbs nutrients efficiently. Integration and Coordination Normal aging results in the loss of few nerve cells. Short- term memory may decline, but overall cognitive skills remain. After age 50, there is a slow decline in the ability to hear higher frequencies, and the lens of the eye does not accommodate as well. Loss of skeletal muscle mass is common but can be controlled through exercise. Bone density declines, which can be slowed by adequate calcium intake and exercise. The Reproductive System 101 Females undergo menopause and are no longer reproductive. In males, sperm production continues until death. Aging Well Good health habits started when young slow the aging process and contribute to a long, healthy life span. Mader VRL CD-ROM Image 0362l.jpg (Fig. 18.15) Image 0363l.jpg (Fig. 18.16) Image 0364l.jpg (Fig. 18B) Image 0365l.jpg (Fig. TA18.1) Case Studies Online Is Dr. Melissa Walker Too Old to Have a Baby? Transparencies 275 (Fig. TA18.1) SEVENTH EDITION CHANGES New/Revised Text: This was chapter 18 in the previous edition. The chapter has been reorganized. The human life cycle, including mitosis and meiosis, now begins the chapter. The chapter ends with a discussion of chromosomal inheritance abnormalities. 19.2 Mitosis contains a new topic Cytokinesis, which discusses cytokinesis and formation of a cleavage furrow. 19.4 Chromosomal Inheritance. The discussion of nondisjunction now precedes an expanded explanation of nondisjunction, how it occurs, and its resulting chromosomal abnormalities. Down syndrome and other syndromes caused by abnormalities in chromosome makeup follow the discussion of nondisjunction. The term triplo-X syndrome has been changed to poly-X syndrome. New Bioethical Focus: Cloning in Humans New/Revised Figures: 19.1 Life cycle of humans; 19.8 Spermatogenesis and oogenesis; 19.9 Human karyotype preparation New/Revised Tables: 19.1 Meiosis I Versus Mitosis; 19.2 Meiosis II Versus Mitosis; These new tables help summarize the information given in the chapter. STUDENT ACTIVITIES Quality of life for the elderly 1. Ask the social director (or equivalent person) of a residential care facility for the elderly to visit the class and discuss the care taken to insure a high quality of life. What are the factors that determine the quality of life for an individual resident? (health, interests, exercise, religious faith, participation in social activities, etc.). What chronic medical problems are most common among the elderly? Planning Pregnancy 2. Students should read the Health Focus, “Preventing Birth Defects,” before coming to class. To introduce a sense of lively competition, divide the class into males and females. Each group is to prepare two lists: (1) decisions to be made before pregnancy occurs and (2) decisions to be made after pregnancy occurs. The Health Focus can be a source of ideas, but other sources are also helpful. Complete sentences must be used; the lists will be judged by their completeness. The group producing the longest and most sensible list receives bonus points to add to their class score. Advantages of Breast-Feeding 3. To help students make the best decisions regarding their future children, have students read the following article: Newman, J. December 1995. How breast milk protects newborns. Scientific American 273(6): 76. Breast milk is the most nutritionally sound choice for newborns and gives them antibodies that boost their immune systems. Have students discuss the social pros and cons of breast-feeding. Some students in your class may have direct experience with this topic. Alternatively, have a representative from the La Leche League speak to your class about breast-feeding and breast milk. 102