1. PowerLecture: Chapter 17 Development and Aging

2. Learning Objectives  Describe early embryonic development and distinguish each of the following: oogenesis, fertilization, cleavage, gastrulation, and organ formation.  Correlate the three germ layers—ectoderm, mesoderm, and endoderm—with the tissues that eventually form from each.  Outline the principal events of prenatal development.

3. Learning Objectives (cont’d)  Describe some of the risks to the early development of the fetus.  Describe the events of aging.

4. Impacts/Issues Fertility Factors and Mind-Boggling Births

5.  Multiple births are becoming more common; twins, triplets, quads, and so on are usually the result of the administration of fertility drugs to the prospective mother.

6. Fertility Factors and Mind-Boggling Births  The rise in higher order multiple births worries some doctors. The risk of miscarriage, premature delivery, and delivery complications is increased. The risk of miscarriage, premature delivery, and delivery complications is increased. Multiples’ birth weights are lower and mortality rates higher. Multiples’ birth weights are lower and mortality rates higher. Parents face more physical, emotional, and financial burdens. Parents face more physical, emotional, and financial burdens.

7. How Would You Vote? To conduct an instant in-class survey using a classroom response system, access “JoinIn Clicker Content” from the PowerLecture main menu.  Should we restrict the use of fertility drugs to conditions that could limit the number of embryos that form? a. Yes, multiple pregnancies are too risky and can lead to serious disabilities or death for infants. a. Yes, multiple pregnancies are too risky and can lead to serious disabilities or death for infants. b. No, reproductive decisions belong to individuals. There are other ways to reduce multiple births. b. No, reproductive decisions belong to individuals. There are other ways to reduce multiple births.

8. Section 1 The Six Stages of Early Development: An Overview

9. The Six Stages of Early Development  In the first three stages, gametes form, an egg is fertilized, and cleavage occurs. Development begins when gametes (sperm and eggs) form and mature in the prospective child’s parents. Development begins when gametes (sperm and eggs) form and mature in the prospective child’s parents. Fertilization occurs when a sperm penetrates an egg; after a series of steps, fertilization produces a zygote. Fertilization occurs when a sperm penetrates an egg; after a series of steps, fertilization produces a zygote. Cleavage converts the zygote into a ball of cells called a morula. Cleavage converts the zygote into a ball of cells called a morula.

10. Fig. 17.1, p. 314 zygote after first cleavage beginning of the ball of cells called a morula

11. The Six Stages of Early Development The number of cells increases but not individual cell size.The number of cells increases but not individual cell size. Each new cell (blastomere) contains a particular portion of the egg’s cytoplasm, which will determine its developmental fate.Each new cell (blastomere) contains a particular portion of the egg’s cytoplasm, which will determine its developmental fate.  In stage four, three primary tissues form. Gastrulation lays out the organizational framework for the body as the cells are arranged into three primary germ layers. Gastrulation lays out the organizational framework for the body as the cells are arranged into three primary germ layers.

12. The Six Stages of Early Development Ectoderm is the outer layer; it gives rise to the nervous system and the outer layers of the integument.Ectoderm is the outer layer; it gives rise to the nervous system and the outer layers of the integument. Mesoderm is the middle layer; muscles as well as organs of circulation, reproduction, excretion, and the skeleton are derived from it.Mesoderm is the middle layer; muscles as well as organs of circulation, reproduction, excretion, and the skeleton are derived from it. Endoderm is the inner layer; it gives rise to the lining of the digestive tube and organs derived from it.Endoderm is the inner layer; it gives rise to the lining of the digestive tube and organs derived from it. Each layer will split into subgroups to give rise to the body’s various tissues and organs. Each layer will split into subgroups to give rise to the body’s various tissues and organs.

14. The Six Stages of Early Development  In stages five and six, organs begin to form, then grow and become specialized. Organogenesis begins as germ layers subdivide into populations of cells destined to become organs and tissues that are unique in structure and function. Organogenesis begins as germ layers subdivide into populations of cells destined to become organs and tissues that are unique in structure and function. Growth and tissue specialization allow organs to grow and acquire functional capabilities. Growth and tissue specialization allow organs to grow and acquire functional capabilities.

15. The Six Stages of Early Development During the first several weeks of development three key processes are at work: During the first several weeks of development three key processes are at work: During cell determination, the eventual developmental path is established.During cell determination, the eventual developmental path is established. In cell differentiation, cells come to have specific structures, products, and functions associated with a specific purpose in the body.In cell differentiation, cells come to have specific structures, products, and functions associated with a specific purpose in the body. Morphogenesis is the organization of differentiated cells into tissues and organs by means of localized cell division, movements of tissues, folding, and the like.Morphogenesis is the organization of differentiated cells into tissues and organs by means of localized cell division, movements of tissues, folding, and the like.

16. Fig. 17.2, p. 315 top view Gamete Formation FertilizationCleavage Gastrulation Organ Formation Growth, Tissue Specialization a Eggs form and mature in female reproductive organs. Sperm form and mature in male reproductive organs. c Cell divisions carve up different regions of egg cytoplasm for daughter cells. d Cell divisions, migrations, and rearrangements produce two or three primary tissues, the start of specialized tissues and organs. e Subpopulations of cells are sculpted into specialized organs and tissues in spatial patterns at prescribed times. f Organs increase in size and gradually assume their specialized functions. b A sperm and an egg fuse at their plasma membrane. Then the nucleus of one fuses with the nucleus of the other to form the zygote

17. Fig. 17.2, p. 315 top view Gamete Formation Fertilization Cleavage Gastrulation Organ Formation Growth, Tissue Specialization a Eggs form and mature in female reproductive organs. Sperm form and mature in male reproductive organs. c Cell divisions carve up different regions of egg cytoplasm for daughter cells. d Cell divisions, migrations, and rearrangements produce two or three primary tissues, the start of specialized tissues and organs. e Subpopulations of cells are sculpted into specialized organs and tissues in spatial patterns at prescribed times. f Organs increase in size and gradually assume their specialized functions. b A sperm and an egg fuse at their plasma membrane. Then the nucleus of one fuses with the nucleus of the other to form the zygote Stepped Art

18. Section 2 The Beginnings of You— Fertilization to Implantation

19.  Fertilization unites sperm and oocyte. Of the millions of sperm deposited in the vagina during coitus, only a few hundred ever reach the upper region of the oviduct where fertilization occurs. Of the millions of sperm deposited in the vagina during coitus, only a few hundred ever reach the upper region of the oviduct where fertilization occurs. The acrosome of the sperm becomes structurally unstable in a process called capacitation.The acrosome of the sperm becomes structurally unstable in a process called capacitation. Many sperm will bind to the zona pellucida of the egg.Many sperm will bind to the zona pellucida of the egg. The Beginnings of You – Fertilization to Implantation

20. Only one sperm will successfully enter the cytoplasm of the secondary oocyte because of changes to the egg’s membrane that prevent entry by additional sperm. Only one sperm will successfully enter the cytoplasm of the secondary oocyte because of changes to the egg’s membrane that prevent entry by additional sperm. The arrival of that sperm inside stimulates the completion of meiosis II in the secondary oocyte, which yields a mature ovum and a second polar body.The arrival of that sperm inside stimulates the completion of meiosis II in the secondary oocyte, which yields a mature ovum and a second polar body. The sperm nucleus fuses with the egg nucleus to restore the human diploid chromosome number of 46.The sperm nucleus fuses with the egg nucleus to restore the human diploid chromosome number of 46. The Beginnings of You – Fertilization to Implantation

21. zona pellucida follicle cell fusion of sperm nucleus with egg nucleus FERTILIZATION OVULATION oviduct ovary uterus opening of cervix vagina sperm enter vagina Fig. 17.3a-d, p. 316 nuclei fuse egg nucleus a b d c

22.  Cleavage produces a multicellular embryo. Repeated divisions of the zygote produce the morula; the cells are not necessarily larger but differ in size, shape, and activity. Repeated divisions of the zygote produce the morula; the cells are not necessarily larger but differ in size, shape, and activity. When the morula reaches the uterus, it transforms into a blastocyst, consisting of a surface layer of cells—the trophoblast—and an inner cell mass, from which the embryo develops. When the morula reaches the uterus, it transforms into a blastocyst, consisting of a surface layer of cells—the trophoblast—and an inner cell mass, from which the embryo develops. Identical twins are the result of a separation of the two cells produced by the first cleavage; fraternal twins are not identical because they are the result of two separate fertilizations. Identical twins are the result of a separation of the two cells produced by the first cleavage; fraternal twins are not identical because they are the result of two separate fertilizations. The Beginnings of You – Fertilization to Implantation

23.  Implantation gives a foothold in the uterus. Implantation into the wall of the uterus takes place about a week after fertilization. Implantation into the wall of the uterus takes place about a week after fertilization. The blastocyst contacts and invades the endometrium; eventually the endometrium willThe blastocyst contacts and invades the endometrium; eventually the endometrium will close over it. Sometimes an ectopic (tubal)Sometimes an ectopic (tubal) pregnancy occurs; this is where the fertilized egg implants outside of the uterus, often in the oviduct, and must be surgically removed. The Beginnings of You – Fertilization to Implantation Figure 17.25

24. The implanted embryo releases HCG (human chorionic gonadotropin), which stimulates the corpus luteum to continue secreting estrogen and progesterone to maintain the uterine lining; the presence of HCG in the mother’s urine is the basis for home pregnancy tests. The implanted embryo releases HCG (human chorionic gonadotropin), which stimulates the corpus luteum to continue secreting estrogen and progesterone to maintain the uterine lining; the presence of HCG in the mother’s urine is the basis for home pregnancy tests. The Beginnings of You – Fertilization to Implantation

25. Days 1-2Day 3Day 4 inner cell mass Day 5 endometrium implantation fertilization Fig. 17.4, p. 317 abcdDays 6-7e endometrium blastocoel trophoblast (surface layer of cells of the blastocyst) uterine cavity inner cell mass fluid The first cleavage furrow extends between the two polar bodies. After the third cleavage, cells form a compact ball By 96 hours there is a ball of 16 to 32 cells. This is the morula. Cells of the surface layer will function in implantation and will give rise to a membrane, the chorion. A fluid-filled cavity forms in the morula. By the 32-cell stage, differentiation is occurring in an inner cell mass that will give rise to the embryo. This embryonic stage is the blastocyst. Some of the blastocyst’s surface cells attach themselves to the endometrium and start to burrow into it. Implantation has started.

26. Days 1-2Day 3Day 4 inner cell mass Day 5 endometrium implantation fertilization Fig. 17.4, p. 317 abcdDays 6-7e endometrium blastocoel trophoblast (surface layer of cells of the blastocyst) uterine cavity inner cell mass fluid Stepped Art

27. Section 3 How the Early Embryo Takes Shape

28.  First, the basic body plan is established. By the time of implantation, the inner cell mass has transformed into a pancake-shaped embryonic disk. By the time of implantation, the inner cell mass has transformed into a pancake-shaped embryonic disk. Gastrulation rearranges the cells into the three germ layers and the primitive streak; ectoderm thickens around the streak to establish the neural tube and notochord, which eventually forms the brain, spinal cord, and vertebral column. Gastrulation rearranges the cells into the three germ layers and the primitive streak; ectoderm thickens around the streak to establish the neural tube and notochord, which eventually forms the brain, spinal cord, and vertebral column.

29. epidermis lined body cavity (coelom); lining also holds internal organs in place peritoneum gut cavity Fig. 17.5a, p. 318

30. How the Early Embryo Takes Shape By week three, blocks of mesoderm called somites form and will give rise to connective tissues, bones, and muscles; pharyngeal arches (face, neck, and associated parts) and the coelom (body cavity) also begin to form. By week three, blocks of mesoderm called somites form and will give rise to connective tissues, bones, and muscles; pharyngeal arches (face, neck, and associated parts) and the coelom (body cavity) also begin to form.

31. primitive streak yolk sac embryonic disk amniotic cavity chorionic cavity a DAY 15. A primitive streak appears along the axis of the embryonic disk. This thickened band of cells marks the onset of gastrulation. Fig. 17.5b, p. 318 future brain somites b DAYS 19-23. Cell migrations, tissue folding, and other morphogenic events lead to the formation of a hollow neural tube and to somites (bumps of mesoderm). The neural tube gives rise to the brain and spinal cord. Somites give rise to most of the axial skeleton, skeletal muscles, and much of the dermis. pharyngeal arches c DAYS 24-25. By now, some cells have given rise to pharyngeal arches, which contribute to the face, neck, mouth, nasal cavities, larynx, and pharynx. neural tube

32. How the Early Embryo Takes Shape  Next, organs develop and take on the proper shape and proportions. Neurulation is the first stage in the development of the nervous system. Neurulation is the first stage in the development of the nervous system. Ectodermal cells at the midline of the embryo elongate to form a neural plate.Ectodermal cells at the midline of the embryo elongate to form a neural plate. Cells of the neural plate fold over and meet at the midline to form a neural tube that will eventually form the spinal cord and brain.Cells of the neural plate fold over and meet at the midline to form a neural tube that will eventually form the spinal cord and brain.

33. How the Early Embryo Takes Shape The folding of sheets of cells is an important part of morphogenesis. The folding of sheets of cells is an important part of morphogenesis. Cells migrate from one place to another by sending out pseudopods that guide them along prescribed routes using adhesive and chemical cues.Cells migrate from one place to another by sending out pseudopods that guide them along prescribed routes using adhesive and chemical cues. Body parts are sculpted by apoptosis, a mechanism of genetically programmed cell death.Body parts are sculpted by apoptosis, a mechanism of genetically programmed cell death. Figures 17.6b and 17.7

34. neural tube Fig. 17.6, p. 319 ectoderm at gastrula stage neural plate formation a b “climbing” nerve cell

35. Section 4 Vital Membranes Outside the Embryo

36.  Four extraembryonic membranes form. The inner cell mass becomes the embryonic disk; some cells will give rise to the embryo, others to the extraembryonic membranes. The inner cell mass becomes the embryonic disk; some cells will give rise to the embryo, others to the extraembryonic membranes. The yolk sac gives rise to the digestive tube and is a source of early blood cells.The yolk sac gives rise to the digestive tube and is a source of early blood cells. The amnion is a fluid-filled sac that keeps the embryo from drying out and acts as a shock absorber; the fluid is amniotic fluid.The amnion is a fluid-filled sac that keeps the embryo from drying out and acts as a shock absorber; the fluid is amniotic fluid. Vital Membranes Outside the Embryo

37. The allantois gives rise to the blood vessels that will become enclosed in the umbilical cord, linking the embryo to the placenta.The allantois gives rise to the blood vessels that will become enclosed in the umbilical cord, linking the embryo to the placenta. The chorion, a protective membrane around the embryo, secretes HCG to maintain the uterine lining after implantation.The chorion, a protective membrane around the embryo, secretes HCG to maintain the uterine lining after implantation. Vital Membranes Outside the Embryo

38. start of amniotic cavity start of embryonic disk start of yolk sac a DAYS 10-11. The yolk sac, embryonic disk, and amniotic cavity have started to form from parts of the blastocyst. Fig. 17.8, p. 320 b DAY. 12 Blood filled spaces form in maternal tissue. The chorionic cavity starts to form. c Day 14 A connecting stalk has formed between the embryonic disk and chorion. Chorionic villi which will be features of a placenta start to form. blood-filled spaces start of chorionic cavity yolk sac chorionic cavity chorionic villi chorion amniotic cavity connecting stalk

39.  The placenta is a pipeline for oxygen, nutrients, and other substances. The placenta is a combination of endometrial tissue and embryonic chorion. The placenta is a combination of endometrial tissue and embryonic chorion. The maternal tissue consists of tissues rich in arterioles and venules.The maternal tissue consists of tissues rich in arterioles and venules. The embryo’s chorion extends into the maternal tissue as tiny chorionic villi.The embryo’s chorion extends into the maternal tissue as tiny chorionic villi. Vital Membranes Outside the Embryo

40. Materials are exchanged between the blood capillaries of mother and fetus where these vessels associate in the blood-filled spaces of the endometrium; exchange is by diffusion. Materials are exchanged between the blood capillaries of mother and fetus where these vessels associate in the blood-filled spaces of the endometrium; exchange is by diffusion. Maternal and fetal bloods do not mix.Maternal and fetal bloods do not mix. Harmful substances, such as alcohol, caffeine, drugs, and even infectious agents such as HIVHarmful substances, such as alcohol, caffeine, drugs, and even infectious agents such as HIV can also cross the placenta. Vital Membranes Outside the Embryo

41. 4 weeks 8 weeks 12 weeks appearance of the placenta at full term Fig. 17.9 (1), p. 321 MATERNAL CIRCULATION mother’s blood vessels tissues of uterus FETAL CIRCULATION embryonic blood vessels umbilical cord space between chorionic villi chorionic villus fused amniotic and chorionic membranes AMNIOTIC FLUID blood passes to and from mother’s vessels

42. Section 5 The First Eight Weeks— Human Features Emerge

43.  The embryonic stage ends as the eighth week draws to a close; by this time morphogenesis has begun to form the features that show us to be human. Figure 17.10 The First Eight Weeks – Human Features Emerge

44. Fig. 17.10a, p. 322 WEEK 4 tail lower limb bud neural tube forming somites upper limb bud developing heart pharyngeal arches future lens forebrain embryo connecting stalk yolk sac a

45. Fig. 17.10b, p. 322 head growth exceeds growth of other regions umbilical cord forms between weeks 4 and 8 (amnion expands, forms tube that encloses the connecting stalk and a duct for blood vessels) upper limb differentiation (hand plates develop, then digital rays of future fingers;wrist, elbow start forming) foot plate future external ear retinal pigment WEEKS 5–6 b

46. Fig. 17.10c, p. 322 WEEK 8 final week of embryonic period; embryo looks distinctly human compared to other vertebrate embryos upper and lower limbs well formed; fingers and then toes have separated early tissues of all internal, external structures now developed tail has become stubby

47.  Gonad development begins by the second half of the first trimester. An embryo with a Y chromosome will have a sex-determining region on the chromosome that triggers the development of testes; testes will produce male hormones that will influence further sex differentiation. An embryo with a Y chromosome will have a sex-determining region on the chromosome that triggers the development of testes; testes will produce male hormones that will influence further sex differentiation. An XX embryo will become a female because of the absence of testosterone; no other hormones are necessary at this point. An XX embryo will become a female because of the absence of testosterone; no other hormones are necessary at this point. The First Eight Weeks – Human Features Emerge

48. 10 weeks Y chromosome present Y chromosome absent 7 weeks birth approaching penis vaginal opening Fig. 17.11, p. 323 birth approaching

49. 10 weeks Y chromosome present Y chromosome absent 7 weeks birth approaching Fig. 17.11, p. 323 vaginal opening birth approaching penis Stepped Art

50.  At the end of eight weeks of development, the embryo is designated a fetus; a heart monitor at this point can detect the fetal heartbeat.  Miscarriage is the spontaneous expulsion of an embryo or fetus. This occurs in about 20% of all conceptions, usually during the first trimester. This occurs in about 20% of all conceptions, usually during the first trimester. More than half of all spontaneous abortions occur because of genetic disorders in the embryo/fetus. More than half of all spontaneous abortions occur because of genetic disorders in the embryo/fetus. The First Eight Weeks – Human Features Emerge

51. Section 6 Development of the Fetus

52. Development of the Fetus  In the second trimester movements begin. The second trimester encompasses the fourth through sixth months. The second trimester encompasses the fourth through sixth months. Fuzzy hair (lanugo) and a cheesy coating (vernix caseosa) cover the body. Fuzzy hair (lanugo) and a cheesy coating (vernix caseosa) cover the body. The sucking reflex is evident, as is movement of the arms and legs; the fetus is about 4-5 inches long at this point. The sucking reflex is evident, as is movement of the arms and legs; the fetus is about 4-5 inches long at this point.

53. Development of the Fetus  Organ systems mature during the third trimester. The third trimester extends from month seven until birth; the earliest delivery in which survival on its own is possible is the middle of this trimester. The third trimester extends from month seven until birth; the earliest delivery in which survival on its own is possible is the middle of this trimester. Babies born before seven months’ gestation often suffer from respiratory distress syndrome. Babies born before seven months’ gestation often suffer from respiratory distress syndrome. Figure 17.12

54. Fig. 17.12(1), p. 324 placenta WEEK 16 Length: 16 cm (6.4 inches) Weight: 200 gm (7 ounces) WEEK 38 (full term) Length: Weight: 50 centimeters (20 inches) 3,400 grams (7.5 pounds) WEEK 29 Length:27.5 centimeters (11 inches) Weight:1,300 grams (46 ounces) placenta

55. Development of the Fetus  The blood and circulatory system of a fetus have special features. Deoxygenated blood is carried from the fetus to the placenta in two umbilical arteries; oxygenated blood is returned to the fetus via the umbilical vein. Deoxygenated blood is carried from the fetus to the placenta in two umbilical arteries; oxygenated blood is returned to the fetus via the umbilical vein. The lungs are bypassed due to the foramen ovale and the ductus arteriosus. The lungs are bypassed due to the foramen ovale and the ductus arteriosus. The ductus venosus allows blood to proceed directly from the placenta to the heart, bypassing the liver. The ductus venosus allows blood to proceed directly from the placenta to the heart, bypassing the liver.

56. aorta superior vena cava foramen ovale liver umbilical vein umbilical cord placenta arterial duct (ductus arteriosus) pulmonary vessels heart venous duct (ductus venous) inferior vena cava allantois umbilical arteries urinary bladder Fig. 17.13a, p. 325

57. closed foramen ovale (fossa ovalis) hepatic vein umbilicus (navel) ligament umbilical ligaments ligamentpulmonary artery pulmonary veins hepatic portal vein serving the liver degenerated allantois (urinary bladder) Fig. 17.13b, p. 325

58. Section 7 Birth and Beyond

59.  Hormones trigger birth. Birth (parturition) usually takes place about 39 weeks after fertilization. Birth (parturition) usually takes place about 39 weeks after fertilization. The process of “labor” begins when the smooth muscles of the uterus begin to contract, stimulated by the hormones oxytocin and prostaglandin. The process of “labor” begins when the smooth muscles of the uterus begin to contract, stimulated by the hormones oxytocin and prostaglandin.  Labor has three stages.

60. Birth and Beyond In the first stage, contractions of the uterine muscles push the fetus against the cervix; the cervical canal dilates to about 10 centimeters, and the amniotic sac ruptures. In the first stage, contractions of the uterine muscles push the fetus against the cervix; the cervical canal dilates to about 10 centimeters, and the amniotic sac ruptures. In the second stage, birth occurs and the fetus is forcefully expelled from the uterus because of contractions and the mother’s urge to push; the baby usually comes out head first (bottom first is called breech position). In the second stage, birth occurs and the fetus is forcefully expelled from the uterus because of contractions and the mother’s urge to push; the baby usually comes out head first (bottom first is called breech position). The third stage occurs after birth; continued contractions force fluid, blood, and the placenta (afterbirth) from the mother’s body and the umbilical cord is severed. The third stage occurs after birth; continued contractions force fluid, blood, and the placenta (afterbirth) from the mother’s body and the umbilical cord is severed.

61. detaching placenta umbilical cord Fig. 17.14, p. 326 placentauterus umbilical cord dilating cervix abc

62. Birth and Beyond  Hormones also control milk production in a mother’s mammary glands. The mammary glands produce a special fluid (colostrum) for the newborn for the first few days; then, under the influence of prolactin, milk production (lactation) occurs. The mammary glands produce a special fluid (colostrum) for the newborn for the first few days; then, under the influence of prolactin, milk production (lactation) occurs. Suckling by the baby stimulates the pituitary to release oxytocin, which in turn forces milk into the ducts of the breast tissue in a positive feedback circuit. Suckling by the baby stimulates the pituitary to release oxytocin, which in turn forces milk into the ducts of the breast tissue in a positive feedback circuit.

63. adipose tissue nipple (a) Breast anatomy. milk-producing mammary gland milk duct (b) Breast of lactating female. Fig. 17.15, p. 327

64. Section 8 Potential Disorders of Early Development

65.  Good maternal nutrition is vital. Maternal diet, especially vitamins and minerals, is important throughout pregnancy for the proper development of the fetal tissues. Maternal diet, especially vitamins and minerals, is important throughout pregnancy for the proper development of the fetal tissues. Folic acid (folate) is vital for preventing spina bifida, a condition where the neural tube does not form properly and the baby is born with an exposed spine. Folic acid (folate) is vital for preventing spina bifida, a condition where the neural tube does not form properly and the baby is born with an exposed spine. Severe restriction of the maternal diet can result in underweight babies; a pregnant woman should expect to gain between 20 and 35 pounds, on average, during pregnancy. Severe restriction of the maternal diet can result in underweight babies; a pregnant woman should expect to gain between 20 and 35 pounds, on average, during pregnancy. Potential Disorders of Early Development

66.  Infections present risks. Risk of infection in the fetus is minimized by maternal antibodies that cross over into the fetal blood. Risk of infection in the fetus is minimized by maternal antibodies that cross over into the fetal blood. However, viral diseases in the mother (such as rubella, or German measles) can cause fetal malformations; such agents act as teratogens. However, viral diseases in the mother (such as rubella, or German measles) can cause fetal malformations; such agents act as teratogens. Potential Disorders of Early Development

67.  Prescription drugs can harm. Thalidomide can cause limb deformities; retinoic acid, such as is found in anti-acne creams, increases the risk of facial and cranial deformities. Thalidomide can cause limb deformities; retinoic acid, such as is found in anti-acne creams, increases the risk of facial and cranial deformities. Antibiotics can be a problem also: tetracycline causes yellowed teeth, and streptomycin causes hearing problems. Antibiotics can be a problem also: tetracycline causes yellowed teeth, and streptomycin causes hearing problems. Potential Disorders of Early Development

68.  Alcohol and other drugs can also harm. Alcohol can cross the Alcohol can cross the placenta and cause many effects collectively known as fetal alcohol syndrome (FAS), which is one of the most common causes of mental retardation in the U.S.; children with FAS never catch up, physically or mentally. Potential Disorders of Early Development Figure 17.18

69. Cocaine, especially crack cocaine, prevents a child’s nervous system from developing normally; affected children are chronically irritable and small for their chronological age. Cocaine, especially crack cocaine, prevents a child’s nervous system from developing normally; affected children are chronically irritable and small for their chronological age. Cigarette smoking can cause miscarriage, stillbirth, and premature delivery; long term studies show that toxic substances build up in the fetuses of nonsmokers who are exposed to second-hand smoke. Cigarette smoking can cause miscarriage, stillbirth, and premature delivery; long term studies show that toxic substances build up in the fetuses of nonsmokers who are exposed to second-hand smoke. Potential Disorders of Early Development

70. Sensitivity to Teratogens Figure 17.17

71. Section 9 Prenatal Diagnosis: Detecting Birth Defects

72.  Medical technology now allows us to detect more than 100 genetic disorders before birth. Amniocentesis samples the fluid within the amnion surrounding the fetus to retrieve sloughed off cells, which can be analyzed for genetic abnormalities. Amniocentesis samples the fluid within the amnion surrounding the fetus to retrieve sloughed off cells, which can be analyzed for genetic abnormalities. Prenatal Diagnosis: Detecting Birth Defects

73. Fig. 17.19a, p. 330

74. Centrifugation Growth for weeks in culture medium Fetal cells A few biochemical analyses with some of the amniotic fluid Quick determination of fetal sex and analysis of purified DNA Biochemical analyses for the presence of genes that cause many different metabolic disorders Removal of about 20ml of amniotic fluid containing suspended cells that were sloughed off from the fetus Additional analysis Fig. 17.19b, p. 330

75. Chorionic villus sampling (CVS) carefully harvests tissue from the placenta for cell analysis. Chorionic villus sampling (CVS) carefully harvests tissue from the placenta for cell analysis. In preimplantation diagnosis, an embryo conceived by IVF is analyzed for genetic defects before it is implanted into the uterus to begin gestation. In preimplantation diagnosis, an embryo conceived by IVF is analyzed for genetic defects before it is implanted into the uterus to begin gestation. Prenatal Diagnosis: Detecting Birth Defects

76. Fetoscopy allows Fetoscopy allows direct visualization of the developing fetus using a fiber-optic device.  All of these procedures carry risks to the unborn fetus. Prenatal Diagnosis: Detecting Birth Defects Figure 17.20

77. Video: Pre-implantation Genetics  This video clip is available in CNN Today Videos for Genetics, 2005, Volume VII. Instructors, contact your local sales representative to order this volume, while supplies last.

78. Section 10 From Birth to Adulthood

79.  There are many transitions from birth to adulthood. Prenatal development occurs before birth; a newborn is referred to as a neonate. Prenatal development occurs before birth; a newborn is referred to as a neonate. The stages of postnatal development are: neonate (first two weeks) >>> infant (two weeks to 15 months) >>> child (to 12 years) >>> pubescent (individual at puberty) >>> adolescent (from puberty to 3–4 years later) >>> adult >>> old age. The stages of postnatal development are: neonate (first two weeks) >>> infant (two weeks to 15 months) >>> child (to 12 years) >>> pubescent (individual at puberty) >>> adolescent (from puberty to 3–4 years later) >>> adult >>> old age.

80. From Birth to Adulthood Certain of these stages are characterized by more noticeable changes such as the growth spurt and the reproductive changes of puberty. Certain of these stages are characterized by more noticeable changes such as the growth spurt and the reproductive changes of puberty. Figure 17.21

81. From Birth to Adulthood  Adulthood is also a time of bodily change. Aging (senescence) is the progressive cellular and bodily deterioration built into the life cycle of all organisms. Aging (senescence) is the progressive cellular and bodily deterioration built into the life cycle of all organisms. Beginning around age 40 there is a gradual decline in bone and muscle mass, increased skin wrinkling, and more fat deposition.Beginning around age 40 there is a gradual decline in bone and muscle mass, increased skin wrinkling, and more fat deposition. Metabolic rates decline, reflexes become slower, and reduced collagen contents make tissues all over the body less elastic.Metabolic rates decline, reflexes become slower, and reduced collagen contents make tissues all over the body less elastic. The definitive causes of aging are not known. The definitive causes of aging are not known.

82. Stages of Human Development

83. Section 11 Time’s Toll: Everybody Ages

84.  Aging is the gradual loss of vitality as body functions become less and less efficient. Skin begins to noticeably wrinkle and sag; body fat accumulates; injuries Skin begins to noticeably wrinkle and sag; body fat accumulates; injuries are more frequent and harder to heal. In the connective tissues, In the connective tissues, more crosslinks form in the collagen, making it less pliable. Time’s Toll: Everybody Ages Figure 17.22

85.  Genes may determine the maximum human life span. Cells may have some internal, biological clock with a predetermined life span. Cells may have some internal, biological clock with a predetermined life span. Support for this idea comes from our knowledge of telomeres, which cap the ends of chromosomes; at each cell division a small bit of telomere is lost until none is left and cell division is no longer possible. Support for this idea comes from our knowledge of telomeres, which cap the ends of chromosomes; at each cell division a small bit of telomere is lost until none is left and cell division is no longer possible. Time’s Toll: Everybody Ages

86.  Cumulative damage to DNA may also play a role in aging. A “cumulative assaults” hypothesis suggests that aging results from mounting damage to DNA combined with a lack of DNA repair. A “cumulative assaults” hypothesis suggests that aging results from mounting damage to DNA combined with a lack of DNA repair. Free radicals of oxygen could cause damage to proteins and mitochondrial DNA.Free radicals of oxygen could cause damage to proteins and mitochondrial DNA. There may be a decline in the ability of cells to repair DNA.There may be a decline in the ability of cells to repair DNA. Aging may ultimately be due to a wide range of controlling factors. Aging may ultimately be due to a wide range of controlling factors. Time’s Toll: Everybody Ages

87. Section 12 Aging Skin, Muscle, Bones, and Reproductive Systems

88.  Changes in connective tissue affect skin, muscles, and bones. Changes in the skin include: slower replacement of epidermis; elastin fibers are replaced with more rigid collagen; fewer oil and sweat glands are present, resulting in drier skin; and loss of hair pigment. Changes in the skin include: slower replacement of epidermis; elastin fibers are replaced with more rigid collagen; fewer oil and sweat glands are present, resulting in drier skin; and loss of hair pigment. Changes in muscle include: loss of mass and strength; muscle replacement by fat. Changes in muscle include: loss of mass and strength; muscle replacement by fat. Aging Skin, Muscle, Bones, and Reproductive Systems

89. Changes in the skeleton are Changes in the skeleton are also seen: bones become weaker, more porous, and brittle due to loss of calcium; intervertebral disks deteriorate, leading to loss of height; joints deteriorate from wear and tear.  Reproductive systems and sexuality change. Aging Skin, Muscle, Bones, and Reproductive Systems Figure 17.23

90. Falling secretions of estrogen and progesterone trigger menopause in women, whereas declining testosterone in men causes reduced fertility. Falling secretions of estrogen and progesterone trigger menopause in women, whereas declining testosterone in men causes reduced fertility. Because the effects of declining hormones may be more troublesome in women, hormone replacement therapy (HRT) may be recommended. Because the effects of declining hormones may be more troublesome in women, hormone replacement therapy (HRT) may be recommended. Despite declines in hormones and other potential problems, men and women both retain their capacity for sexual response well into old age. Despite declines in hormones and other potential problems, men and women both retain their capacity for sexual response well into old age. Aging Skin, Muscle, Bones, and Reproductive Systems

91. Section 13 Age-Related Changes in Some Other Body Systems

92.  The nervous system and senses decline. Neurons are generally not replaced when they die, regardless of age. Neurons are generally not replaced when they die, regardless of age. Neurofibrillary tangles may Neurofibrillary tangles may form inside the neurons, and beta amyloid plagues may form between neurons; both of these are present in people with Alzheimer’s disease (AD). Age-Related Changes in Some Other Body Systems Figure 17.24a-b

93. AD manifests with progressive memoryAD manifests with progressive memory loss and disruptive personality changes. Low levels of acetylcholine and chronicLow levels of acetylcholine and chronic inflammation of brain tissue may also be part of the cause of AD. No effective treatment for AD currentlyNo effective treatment for AD currentlyexists. Persons who inherit one version of a gene that codes for apolipoprotein E are at significantly higher risk for Alzheimer’s disease.Persons who inherit one version of a gene that codes for apolipoprotein E are at significantly higher risk for Alzheimer’s disease. All of us will experience some short-term memory loss as we age, as well as less efficient responses to many stimuli. All of us will experience some short-term memory loss as we age, as well as less efficient responses to many stimuli. Age-Related Changes in Some Other Body Systems Figure 17.24c

94.  The cardiovascular and respiratory systems deteriorate. Changes to the respiratory system are mainly due to the breakdown of the alveoli, resulting in less respiratory surface. Changes to the respiratory system are mainly due to the breakdown of the alveoli, resulting in less respiratory surface. Changes in the cardiovascular system include reduction in heart pumping capacity, stiffening of blood vessels, and deposition of plaque in the vessels. Changes in the cardiovascular system include reduction in heart pumping capacity, stiffening of blood vessels, and deposition of plaque in the vessels. The combined effect of deterioration of these systems is less efficient blood transport. The combined effect of deterioration of these systems is less efficient blood transport. Age-Related Changes in Some Other Body Systems

95.  The immune, digestive, and urinary systems become less efficient. The numbers of T cells drops, B cells become less active, and autoimmune diseases can occur, possibly due to mutations in self- markers. The numbers of T cells drops, B cells become less active, and autoimmune diseases can occur, possibly due to mutations in self- markers. Fewer digestive enzymes are produced in the intestines and basal metabolic rate falls, resulting in weight gain if not compensated for by changes to diet and exercise. Fewer digestive enzymes are produced in the intestines and basal metabolic rate falls, resulting in weight gain if not compensated for by changes to diet and exercise. Urinary incontinence may also occur, particularly in women who have borne children. Urinary incontinence may also occur, particularly in women who have borne children. Age-Related Changes in Some Other Body Systems