Inquiry Into Life 17th Edition Chapter 22 Development And Aging Lecture Outline PDF

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Because learning changes everything. ® INQUIRY INTO LIFE Seventeenth Edition Sylvia S. Mader Michael Windelspecht Chapter 22 Development and Aging Lecture Outline © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC.  22.1 Fertilization and Early Stages of Development Animal development begins with a single cell that multiplies and changes in structure and function to form a complete organism. © McGraw Hill LLC 2  Fertilization 1 Fertilization is the union of a sperm and an oocyte, resulting in a zygote. A sperm cell has three parts: Head, middle piece, and tail. The head contains a nucleus capped by a membrane-bounded acrosome. The oocyte plasma membrane is surrounded by an extracellular matrix, zona pellucida. The zona pellucida is in turn surrounded by layers of adhering follicle cells called the corona radiata. © McGraw Hill LLC 3  Fertilization 2 Stages of fertilization. 1. Sperm squeezes through corona radiata. 2. Sperm releases acrosomal enzymes so it can penetrate the zona pellucida. 3. Sperm cell membrane fuses with oocyte cell membrane. 4. Sperm nucleus enters oocyte, chromatin is released. 5. Cortical granules of oocyte secrete enzymes that turn the zona pellucida into a fertilization membrane. 6. Sperm chromatin reorganizes into a sperm pronucleus that fuses with egg pronucleus. © McGraw Hill LLC 4  Fertilization 3 Figure 22.1 Access the text alternative for slide images. © McGraw Hill LLC 5  Fertilization 4 Normally, one out of hundreds of sperm that reach the oocyte is able to penetrate the egg. Polyspermy is an event that occurs if more than one sperm penetrates the egg. Would result in abnormal chromosome number with abnormal development. Oocyte’s plasma membrane depolarizes (from −65 millivolts to 10 millivolts), and this prevents binding of any other sperm. In addition, the zona pellucida lifts away from oocyte surface, which prevents sperm from binding. © McGraw Hill LLC 6  Early Stages of Animal Development The early stages of animal development occur at the cellular, tissue, and organ levels of organization. © McGraw Hill LLC 7  Cellular Stages of Development 1 The cellular stages of development are cleavage and blastula formation. Cleavage results in a multicellular embryo. Cell divisions without growth in size. Increases number of cells but not total volume of cytoplasm. Divisions of zygote are equal. Forms a multicellular stage called a morula (ball of cells). Formation of the blastula follows. Hollow ball of cells. Fluid-filled cavity is called a blastocoel. © McGraw Hill LLC 8  Lancelet Early Development Figure 22.2 Access the text alternative for slide images. © McGraw Hill LLC (a): Patrick J. Lynch/Science Source 9  Cellular Stages of Development 2 Zygotes of other animals undergo cleavage and form a morula. In frogs, cleavage is not equal because of a yolk. When yolk is present, the zygote and embryo exhibit polarity because the embryo has an animal pole and a vegetal pole. A chicken lays a hard-shelled egg with a large amount of yolk. In a developing chick, the yolk does not participate in cleavage. © McGraw Hill LLC 10  Cellular Stages of Development 3 All vertebrates have a blastula stage, but the appearance may be different. In chicks, the blastula forms a layer of cells that spreads over the yolk. Human blastulas resemble chick blastulas even though we have little yolk. © McGraw Hill LLC (chick): iStock/Getty Images 11  Tissue Stages of Development 1 Two tissue stages of development: 1) Early gastrula—when certain cells begin to push into blastocoel. Creates a double layer of cells. Cells migrate to destinations. 2) Late gastrula. © McGraw Hill LLC 12  Tissue Stages of Development 2 Gastrulation. Involves formation of three layers of cells that will develop into organs. Early gastrula—has two cell layers. Ectoderm—outer layer of cells. Endoderm—inner layer of cells. Lines the archenteron, or primitive gut. Pore created by invagination is the blastopore. Late gastrula—has three layers of cells. A middle mesoderm layer is formed. © McGraw Hill LLC 13  Comparative Development of Mesoderm 1 In the lancelet, the Figure 22.3a mesoderm forms by an outpocketing of the archenteron. Outpocketings grow until they meet and fuse, forming two layers of mesoderm. Space between the layers is a body cavity called the coelom. Access the text alternative for slide images. © McGraw Hill LLC 14  Comparative Development of Mesoderm 2 In the frog, the yolk cells do Figure 22.3b not invaginate; cells remaining are yolk plug. Animal pole cells move over yolk and form slit-like blastopore. The mesoderm forms by migration of cells between the ectoderm and endoderm. Mesoderm split creates coelom. Access the text alternative for slide images. © McGraw Hill LLC 15  Comparative Development of Mesoderm 3 In the chicken egg, the Figure 22.3c endoderm is not formed by invagination due to yolk. Upper cell layer becomes ectoderm; lower cell layer becomes endoderm. The mesoderm forms by invagination along longitudinal furrow. Furrow is primitive streak. Mesoderm later splits to form coelom. Access the text alternative for slide images. © McGraw Hill LLC 16  Comparative Development of Mesoderm 4 Figure 22.3 Gastrulation forms the three germ layers: Ectoderm. Mesoderm. Endoderm. Access the text alternative for slide images. © McGraw Hill LLC 17  Embryonic Germ Layers TABLE 22.1 Embryonic Germ Layers Embryonic Germ Layer Vertebrate Adult Structures Ectoderm (outer layer) Nervous system; epidermis of skin; epithelial lining of oral cavity and rectum Mesoderm (middle layer) Musculoskeletal system; dermis of skin; cardiovascular system; urinary system; reproductive system—including most epithelial linings; outer layers of respiratory and digestive systems Endoderm (inner layer) Epithelial lining of digestive tract and respiratory tract, associated glands of these systems, epithelial lining of urinary bladder © McGraw Hill LLC 18  Organ Stages of Development 1 Germ layers—organs of an animal develop from three embryonic germ layers. Notochord. Supporting rod formed from mesoderm. Forms as mesodermal cells along longitudinal axis of the embryo coalesce. Persists in the lancelet, but is replaced by the vertebral column in vertebrates. © McGraw Hill LLC 19  Organ Stages of Development 2 The nervous system develops from the ectoderm above notochord. Neural plate—thickening of ectoderm above notochord forms neural plate. Neural tube—neural folds moving upward and joining form the neural tube. The embryo is now referred to as a neurula. In later stages, the anterior end of the neural tube becomes the brain, and the rest of the neural tube becomes the spinal cord. © McGraw Hill LLC 20  Development of Neural Tube and Coelom in a Frog Embryo 1 Figure 22.4a–c Access the text alternative for slide images. © McGraw Hill LLC 21  Development of Neural Tube and Coelom in a Frog Embryo 2 Figure 22.4a Access the text alternative for slide images. © McGraw Hill LLC 22  Development of Neural Tube and Coelom in a Frog Embryo 3 Figure 22.4b Access the text alternative for slide images. © McGraw Hill LLC 23  Development of Neural Tube and Coelom in a Frog Embryo 4 Figure 22.4c Access the text alternative for slide images. © McGraw Hill LLC 24  Organ Stages of Development 3 Additional developments. The neural crest is a band of cells that forms where the neural tube pinches off from the ectoderm. Neural crest cells migrate to contribute to skin and muscles, in addition to the adrenal medulla and ganglia of the peripheral nervous system. © McGraw Hill LLC 25  Vertebrate Embryo (Cross-Section) Figure 22.5 Access the text alternative for slide images. © McGraw Hill LLC 26  Organ Stages of Development 4 Midline mesodermal cells that did not contribute to notochord formation become two longitudinal masses of tissue. These masses become blocks called somites, arranged along both sides of the notochord. Somites give rise to muscles associated with the axial skeleton and vertebrae. A primitive gut tube is formed by the endoderm as the body folds into a tube. The heart begins as a simple tubular pump. © McGraw Hill LLC 27  22.2 Processes of Development In addition to growth, the process of development requires three things. Cellular differentiation. Cells become specialized in structure and function. Morphogenesis. Produces the shape and form of the body. Includes pattern formation. How tissues and organs are arranged in the body. © McGraw Hill LLC 28  Cellular Differentiation 1 Somatic cell cloning shows that every cell in the body contains all the genes necessary to develop into an organism. The process of differentiation is made clearer when we consider that specialized cells produce only certain proteins. Genes are not parceled out; rather, differential gene expression accounts for cellular differentiation. Certain genes and not others are turned on in differentiated cells. © McGraw Hill LLC 29  Cellular Differentiation 2 Investigations show that frog egg cytoplasm is different in different regions. Egg has polarity—both a dorsal/ventral and anterior/posterior axis. Axes correlated to gray crescent: visible after fertilization. Classic experiment: gray crescent contains chemical signals. If egg is divided so both halves get gray crescent, then two complete embryos develop. If egg is divided so only half gets gray crescent, then that half develops into an embryo and the other half stops developing. © McGraw Hill LLC 30  Experimental Determination of Cytoplasmic Influence on Development Figure 22.6 Access the text alternative for slide images. © McGraw Hill LLC 31  Cytoplasmic Segregation 1 Frog experiment demonstrates existence of maternal determinants that influence development. Maternal determinants are RNAs and proteins synthesized by maternal genome and stored in egg. Cytoplasmic segregation is the parceling out of maternal determinants (like the gray crescent) that occurs during mitosis. Determines how cells of the morula will develop. Specialization of cells is influenced by maternal determinants and signals from neighboring cells. © McGraw Hill LLC 32  Cytoplasmic Segregation 2 Access the text alternative for slide images. © McGraw Hill LLC 33  Induction Induction is the ability of one embryonic tissue to influence another by chemical signals. Inducers are the chemical signals. Alter metabolism of receiving cell. Activate particular genes. © McGraw Hill LLC 34  Induction and Frog Experiments 1 Gray crescent becomes dorsal lip of blastopore, where gastrulation begins. Dorsal blastopore lip in frog is the primary organizer because it is necessary for complete development. Cells closest to the primary organizer become endoderm, those farthest become ectoderm, and those in the middle become mesoderm. Molecular concentration gradient may act as inducer. © McGraw Hill LLC 35  Induction and Frog Experiments 2 Location of the gray crescent indicates the dorsal surface. Mesoderm here forms the notochord. Ectoderm here becomes nervous system. Notochord induces ectoderm to become the neural plate. Transplanted presumptive notochord tissue causes ectoderm beneath it to differentiate into nervous tissue. Signals from presumptive notochord cause ectoderm to differentiate into nervous tissue. © McGraw Hill LLC 36  Induction and Frog Experiments 3 Another example of induction. Vertebrate eye. Optic vesicle, a lateral outgrowth of the developing brain, induces overlying ectoderm to thicken and become the lens. Lens then induces the optic vesicle to form an optic cup, where the retina forms. © McGraw Hill LLC 37  Induction and Roundworm Experiments 1 Work with Caenorhabditis elegans has shown that induction is necessary for differentiation. Investigators have been able to easily examine the developmental process from beginning to end as the roundworm is transparent. A good model—easily raised, contains only 959 cells in adult, measures only 1 millimeter long. © McGraw Hill LLC 38  Induction and Roundworm Experiments 2 Fate maps are diagrams that trace the differentiation of developing cells. Maps have been developed to show the destiny of each cell of C. elegans as it arises. Detailed studies of the vulva (pore through which eggs are laid) have been performed. A cell called the anchor cell induces the vulva to form. The cell closest to the anchor cell receives the most inducer to become the inner vulva. This cell, in turn, produces another inducer to act on its neighboring cells that become the outer vulva. © McGraw Hill LLC 39  Development of C. Elegans, a Nematode Figure 22.7 Access the text alternative for slide images. © McGraw Hill LLC 40  Morphogenesis Morphogenesis produces the shape and form of the body. Pattern formation is the ultimate in morphogenesis. Refers to how arrangement of body parts come about during development. Fruit fly experiments have contributed to our knowledge of pattern formation. © McGraw Hill LLC 41  Morphogen Genes Morphogen genes determine relationship of individual parts. Some genes control which end becomes the head and which becomes the tail. Other morphogen genes determine how many segments the body will have. © McGraw Hill LLC 42  Morphogen Gradients Morphogen genes code for proteins that are present in a morphogen gradient. Cells at one end contain high levels of the protein; cells at the other end have low levels. Morphogen gradients determine the shape of the organism. Efficient because it can have a range of effects depending on concentration in a portion. Sequential sets of master genes code for morphogen gradients that activate the next set of master genes, etc. © McGraw Hill LLC 43  Morphogen Gradients in the Fruit Fly Protein gradient in Figure 22.8 (a) determines which end is head and which is tail. Gradient in (b) of another protein determines number of segments. Access the text alternative for slide images. © McGraw Hill LLC (both): Steve Paddock, Howard Hughes Medical Research Institute 44  Homeotic Genes 1 Homeotic genes (example: Hox family of genes) control identity of each segment. Encode master regulatory proteins that control expression of other genes, which encode segment-specific structures. Found in many organisms. All share a sequence of nucleotides called a homeobox. Codes for a sequence of 60 amino acids called a homeodomain. Homeodomain protein binds to DNA and determines which genes are turned on. © McGraw Hill LLC 45  Pattern Formation in Drosophila 1 Figure 22.9a Mutations in homeotic genes cause structures to develop where they should not. © McGraw Hill LLC (a): David Scharf/ Science Source 46  Pattern Formation in Drosophila 2 Figure 22.9b top Homologous homeotic genes occur on a fly chromosome and on four mouse chromosomes in the same order (black boxes indicate genes that aren’t identical). © McGraw Hill LLC 47  Pattern Formation in Drosophila 3 Figure 22.9b bottom Color-coded regions correspond to where each homeotic gene regulates pattern formation in the embryo and adult. Access the text alternative for slide images. © McGraw Hill LLC 48  Homeotic Genes 2 Drosophila homeotic genes are located on a single chromosome. In mice and humans, four clusters of homeotic genes are located on four chromosomes. Access the text alternative for slide images. © McGraw Hill LLC 49  Homeotic Genes 3 Homeotic genes are expressed from anterior to posterior in the same order. First clusters determine development of anterior segments. Later clusters determine development of posterior segments. Homeotic genes of many different organisms contain the same homeodomain: indicates this sequence originated early in evolutionary history. © McGraw Hill LLC 50  Apoptosis Apoptosis plays a role in pattern formation. Human hands and feet are shaped by apoptosis. Fate maps of C. elegans indicate that apoptosis occurs in 131 cells. The cell receives a death signal. An inhibiting protein becomes inactivated. A cell-death cascade is allowed to proceed. Enzymes destroy the cell. © McGraw Hill LLC 51  22.3 Human Embryonic and Fetal Development In humans, about 9 months elapse from conception to birth. Development before birth is divided into two phases. Embryonic development—months 1 and 2. Development of major organs. Fetal development—months 3 to 9. Refinement of organ systems. © McGraw Hill LLC 52  Extraembryonic Membranes 1 Extraembryonic membranes lie outside of the embryo. For land animals, they provide oxygen, waste removal, prevention of desiccation, and a protective cushion. Chicks have four extraembryonic membranes. Chorion: lies next to the shell; functions in gas exchange. Amnion: contains amniotic fluid that bathes embryo. Allantois: collects nitrogenous wastes. Yolk sac: surrounds yolk, which provides nourishment. © McGraw Hill LLC 53  Extraembryonic Membranes 2 Figure 22.10a Access the text alternative for slide images. © McGraw Hill LLC 54  Extraembryonic Membranes 3 Humans and other mammals also have extraembryonic membranes. They have been modified to suit internal development, unlike birds and reptiles. Their presence indicates the human relationship to birds and reptiles. All chordate animals develop in water, either bodies of water or within amniotic fluid. © McGraw Hill LLC 55  Extraembryonic Membranes 4 Figure 22.10b Access the text alternative for slide images. © McGraw Hill LLC 56  Embryonic Development 1 The First Week. Fertilization occurs within the distal third of a uterine tube. The zygote undergoes the first cleavage divisions as it migrates through the uterine tube toward the uterus. After about 3 days, embryo is in the morula stage and reaches the uterus. At day 5, embryo has become a blastocyst. Outer layer of trophoblast cells (will become the chorion later). The inner cell mass becomes the embryo. © McGraw Hill LLC 57  Embryonic Development 2 The Second Week. Implantation begins as trophoblast cells secrete digestive enzymes to digest away some of the endometrium. Trophoblast cells begin to secrete human chorionic gonadotropin (HCG). As the week progresses, the inner cell mass detaches itself from the trophoblast. Two more extraembryonic membranes form. Yolk sac: site of first blood cell formation. Amnion: has cavity where embryo develops in amniotic fluid. © McGraw Hill LLC 58  Human Development Before Implantation 4 Figure 22.11 Access the text alternative for slide images. © McGraw Hill LLC 59  Embryonic Development 3 The Second Week. Gastrulation occurs—the inner cell mass has flattened into the embryonic disk. At this stage, ectoderm above and endoderm below. The embryonic disk elongates to form the primitive streak. Mesoderm forms by invagination along the streak. Trophoblast is reinforced by mesoderm and becomes the chorion. © McGraw Hill LLC 60  Human Embryonic Development 1 Figure 22.12a Access the text alternative for slide images. © McGraw Hill LLC 61  Human Embryonic Development 2 Figure 22.12b Access the text alternative for slide images. © McGraw Hill LLC 62  Embryonic Development 4 The Third Week. The nervous system becomes visually evident. Thickening appears along dorsal length of embryo. Invagination occurs as neural folds appear. The neural folds meet at the midline, forming the neural tube, which will later develop into the brain and spinal cord. Development of the heart begins. At first there are right and left heart tubes. After the tubes fuse, the heart begins pumping blood. © McGraw Hill LLC 63  Human Embryonic Development 3 Figure 22.12c Access the text alternative for slide images. © McGraw Hill LLC 64  Human Embryonic Development 4 Figure 22.12d Access the text alternative for slide images. © McGraw Hill LLC 65  Embryonic Development 5 The Fourth and Fifth Weeks. The body stalk (mesoderm) connects the caudal (tail) end of the embryo with the chorion. The chorion has tree-like projections called chorionic villi. The fourth extraembryonic membrane (allantois) is contained within the stalk. Its blood vessels become umbilical blood vessels. The umbilical cord forms, which connects the embryo to the placenta. Limb buds appear. Head enlarges; sense organs are distinguishable. © McGraw Hill LLC 66  Human Embryonic Development 5 Figure 22.12e Access the text alternative for slide images. © McGraw Hill LLC 67  Human Embryo at Beginning of Fifth Week Figure 22.13 Access the text alternative for slide images. © McGraw Hill LLC (a): Anatomical Travelogue/Science Source 68  Embryonic Development 6 The Sixth Through Eighth Weeks. The embryo becomes recognizable as a human. The head achieves its normal relationship to the body as the neck develops. The nervous system continues to develop. Reflexes are present. All organ systems are now established even though the embryo weighs less than 1 gram. © McGraw Hill LLC 69  Fetal Development 1 The Third and Fourth Months. The head is relatively large, the nose is flat, and the eyes are far apart. Epidermal structures develop. Eyelashes, hair on head, eyebrows, fingernails, and nipples Cartilage begins to be replaced by bones. Sex of the individual may be determined. In the fourth month, the heartbeat can be heard. © McGraw Hill LLC 70  Three- to Four-Month-Old Fetus Figure 22.14 © McGraw Hill LLC John Watney/Science Source 71  Fetal Development 2 The Fifth Through Seventh Months. The mother begins to feel movement. Fetal skin is covered by fine hair called lanugo. The skin is also covered with a thick, cheesy coating called the vernix caseosa. Eyelids are open. Survival is now possible if birth occurs prematurely. © McGraw Hill LLC 72  Fetal Development 3 Fetal Circulation. A fetus does not use its lungs for gas exchange. Blood entering the right atrium is shunted through the left atrium through the oval opening (foramen ovale). Any blood that enters the right ventricle ends up being shunted into the aorta by way of the arterial duct (ductus arteriosus). Blood in the aorta is distributed to iliac arteries, which connect to the umbilical arteries leading to the placenta. © McGraw Hill LLC 73  Fetal Development 4 Fetal Circulation. The exchange of gases and nutrients between the fetus and mother occurs in the placenta. Blood leaves the placenta via the umbilical vein. The umbilical vein carries blood to the fetal liver and joins the venous duct (ductus venosus), which merges with the inferior vena cava. The inferior vena cava returns blood to the heart. © McGraw Hill LLC 74  Fetal Circulation and the Placenta 1 Figure 22.15a Access the text alternative for slide images. © McGraw Hill LLC 75  Fetal Circulation and the Placenta 2 Figure 22.15b Access the text alternative for slide images. © McGraw Hill LLC 76  Fetal Development 5 Fetal Circulation. The umbilical arteries and vein are contained in the umbilical cord, which is cut at birth. At birth, the lungs expand, blood enters the lungs, and blood returning to the left atrium should cause a flap to close off the foramen ovale. Failure to close can usually be corrected. The ductus arteriosus closes as endothelial cells proliferate. Remains of the arterial duct and umbilical vessels are converted to connective tissue. © McGraw Hill LLC 77  Fetal Development 6 Structure and Function of the Placenta. The placenta is attached to the uterine wall by the allantois and chorionic villi. The placenta begins to form after embryo is fully implanted. The placenta is fully formed by the tenth week. Produces progesterone and estrogen. Hormones function to prevent new follicles from maturing and maintain lining of uterus. Functions in gas, nutrient, and waste exchange between the fetal and maternal circulatory systems. © McGraw Hill LLC 78  Fetal Development 7 Structure and Function of the Placenta. Placenta has a fetal side contributed by the chorion and a maternal side of uterine tissues. Fetal and maternal blood do not mix. Exchange occurs across the chorionic villi surrounded by maternal blood. The umbilical cord functions to take fetal blood to and from the placenta. Harmful substances (example: alcohol, some medications) can cross the placenta and cause irreversible birth defects. © McGraw Hill LLC 79  22.4 Human Pregnancy, Birth, and Lactation Pregnancy. Many changes occur in the mother’s body during pregnancy due to the hormones progesterone and estrogen. Other factors are due to an increase in size of the uterus from 60 to 80 grams to 900 to 1,200 grams at term. © McGraw Hill LLC 80 Morning Sickness and Energy Level Nausea, vomiting, loss of appetite, and fatigue may be experienced by the mother about 6 weeks into the pregnancy. These symptoms usually subside by the twelfth week. Subsequently, some mothers feel more energetic or have a general sense of well-being. The weight gain is due to breast and uterine enlargement, fetal weight, amniotic fluid, size of placenta, and body fluid increase. © McGraw Hill LLC 81  Effects on Smooth Muscle Progesterone relaxes smooth muscle in uterus and artery walls. Arteries expand, leading to low blood pressure. Sets in motion the renin–angiotensin–aldosterone mechanisms that promotes sodium and water retention. Blood volume increases by 40%; red blood cells increase; cardiac output increases; blood flow to kidneys, placenta, skin, and breasts rises. Smooth muscle relaxation of esophageal sphincter leads to reflux and heartburn. Constipation may result from decreased intestinal tract motility. © McGraw Hill LLC 82  Other Effects Enlarged uterus causes compression of ureters and bladder, which can result in incontinence. Inferior vena cava also compressed, leading to edema and varicose veins. Placenta produces some peptide hormones. May make cells resistant to insulin, leading to gestational diabetes. May cause stretch marks over abdomen and lower breast area. Melanocyte activity increases, causing darkening of certain areas of the skin. © McGraw Hill LLC 83  Birth 1 During the last trimester. Contractions occur that are light at first (15 to 20 minutes) but become stronger and more frequent toward the end of pregnancy. At onset of true labor, contractions occur every 10 to 15 minutes, and last 40 seconds or longer. A positive feedback mechanism is involved. Stretching of the cervix causes oxytocin release and uterine contractions. Oxytocin stimulates further uterine contractions, which push fetus downward and stretch cervix more. More oxytocin is then released. © McGraw Hill LLC 84  Birth 2 Events occur that indicate delivery will soon occur: Uterine contractions occur about every 5 minutes and become stronger. The “water breaks,” meaning the amnion has ruptured and the amniotic fluid is released. A mucus plug (from the cervix) is expelled. The plug prevents bacteria and sperm from entering the vagina during pregnancy. © McGraw Hill LLC 85  Birth 3 Parturition, process of giving birth, can be divided into three stages. Stage 1. At first, uterine contractions occur such that the cervical canal slowly disappears as the lower part of the uterus is pulled toward the baby’s head (effacement). The baby’s head acts as a wedge to assist in cervical dilation during subsequent contractions. The amniotic membrane will rupture, releasing amniotic fluid. This stage ends when the cervix is fully dilated. © McGraw Hill LLC 86  Birth 4 Stage 2. Uterine contractions occur every 1 to 2 minutes and last about a minute. The baby’s head gradually descends into the vagina, with an increased desire to push. The baby’s head reaches the exterior and turns so that the back of the head is uppermost. An incision called an episiotomy may be needed. As soon as the head is delivered, the baby’s shoulders rotate so that the baby faces left or right. The rest of the baby follows easily. © McGraw Hill LLC 87  Birth 5 After the baby is breathing, the umbilical cord is cut and tied. The stump of the cord shrivels and leaves a scar, the umbilicus (navel). Stage 3. The placenta (afterbirth) is delivered. About 15 minutes after delivery, uterine muscular contractions shrink the uterus to dislodge the placenta and membranes. The placenta is expelled into the vagina and then delivered. © McGraw Hill LLC 88  Three Stages of Parturition (Birth) Figure 22.16 Access the text alternative for slide images. © McGraw Hill LLC 89  Female Breast and Lactation 1 Each breast contains 15 to 25 lobules. Each lobule has a milk duct that branches from the nipple into numerous smaller ducts that terminate in alveoli. During pregnancy, the breasts enlarge as the number of ducts and alveoli increase. Prolactin stimulates milk synthesis. Inhibited by estrogen and progesterone during pregnancy. When placenta is delivered, the anterior pituitary produces prolactin. © McGraw Hill LLC 90  Female Breast and Lactation 2 First secretions are colostrum, which is a thin, milky fluid rich in protein and antibodies. The stimulus from suckling causes oxytocin release. Oxytocin causes milk letdown into the ducts. Breast milk contains antibodies produced by the mother that help prevent infections and illnesses in the baby. Breast-feeding can help the uterus return to its normal size. © McGraw Hill LLC 91  Female Breast Anatomy Figure 22.17 © McGraw Hill LLC 92  22.5 Aging 1 Development continues even after birth. Infancy, toddler, preschooler—birth to 5 years. Acquire gross and fine motor skills, language use begins, maturation of senses, socialization. Childhood and preadolescence—6 to 12 years. Continued rapid growth; identity apart from parents; peer approval. Adolescence—onset of puberty; sexual maturation occurs. Begins at ages 10 to 14 in girls; 12 to 16 years in males. Adulthood—social and psychological changes in transition to adulthood. © McGraw Hill LLC 93  22.5 Aging 2 Aging encompasses these progressive changes, which contribute to an increased risk of infirmity, disease, and death. Gerontology is the study of aging—of great interest in a society that includes more older individuals than ever. Goal is not to necessarily increase life span, but rather health span, the number of years that an individual has full functions of all body parts and processes. © McGraw Hill LLC 94  Factors Influencing Aging 1 Aging is a complex process affected by multiple factors. Aging is partly genetically preprogrammed. Longevity runs in families. Identical twins have a similar life span. © McGraw Hill LLC 95  Factors Influencing Aging 2 Hormones. Single-gene mutations have been shown to influence the life span. C. elegans studies have shown that single-gene mutations can influence life span. Mutations of a hormone receptor gene more than doubled the life span of the worms. Small-breed dogs have lower levels of an analogous receptor and live longer than large-breed dogs. © McGraw Hill LLC 96  Factors Influencing Aging 3 Telomeres are sequences of DNA that protect the ends of chromosomes from deteriorating or fusing with other chromosomes. Each time a cell divides, the telomeres normally shorten. Telomerase replenishes the length of the telomeres in some cells. Studies show that using stem cells and cancer cells that both possess telomerase have slowed down the aging process in mice. © McGraw Hill LLC 97  Factors Influencing Aging 4 Mitochondria and diet: Mitochondria generate free radicals that damage nutrient molecules and cause the cell to lose internal functions. Free radicals damage DNA and proteins. High-calorie diets increase the level of free radicals and accelerate cell aging. Low-calorie diets and consumption of antioxidants can extend the life span. © McGraw Hill LLC 98  Factors Influencing Aging 5 Damage accumulation: Aging involves the accumulation of damage over time. Life expectancy has changed from 45 years in 1900 to an average of 78 currently. Human genes have not changed in such a short time. Increased life expectancy is mostly due to better medical care. Increased life expectancy is also due to the application of scientific knowledge about how to prolong lives. © McGraw Hill LLC 99  Factors Influencing Aging 6 There are two basic types of cellular damage that accumulate over time. The first type—unavoidable agents. Accumulation of harmful DNA mutations or buildup of harmful metabolites. Proteins may become increasingly cross-linked. Blood vessels, the heart, and lungs function less effectively when their collagen is cross-linked. Glucose has the tendency to attach to any type of protein, beginning cross-linking. The second type—avoidable agents: poor diet, exposure to sun. © McGraw Hill LLC 100  The Effects of Aging on Organ Systems 1 Integumentary System. Skin becomes thinner, less elastic, and has less subcutaneous fat. Causes wrinkles, decreased insulation. Sweat glands become less active, resulting in decreased tolerance to high temperatures. Fewer hair follicles: the hair thins out. Fewer melanocytes: hair gray and skin pale. Remaining pigmented cells are larger and result in pigmented blotches (age spots). © McGraw Hill LLC 101  The Effects of Aging on Organ Systems 2 Cardiovascular System. Cardiovascular problems are usually related to disease, especially atherosclerosis. Heart weakens and may increase in size. Heart rate decreases. Resting heart rate and blood pressure return more slowly following stress. Blood pressure increases as vessels become more rigid and decrease in internal diameter. © McGraw Hill LLC 102  The Effects of Aging on Organ Systems 3 Immune System. As people age, many of their immune system functions become compromised. The reduced ability to protect against infections, toxins, and some types of cancer is thought to play a role in the aging process. Thymus involutes and decreases in size. The thymus of a 60-year-old is about 5% the size of a newborn, leading to reduced T cell responses. Antibody responses consequently decline because most B cell responses depend on T cells. © McGraw Hill LLC 103  The Effects of Aging on Organ Systems 4 Digestive System. Less affected by aging than other systems. Saliva secretion decreases, which causes more bacteria to adhere to the teeth. This results in more tooth decay and periodontal disease. Blood flow to the liver is reduced, and the liver does not metabolize drugs as efficiently. Smaller doses of medications are needed. © McGraw Hill LLC 104  The Effects of Aging on Organ Systems 5 Respiratory System. Respiratory disorders often accompany cardiovascular disease. Decreasing elasticity of lung tissues leads to a reduction in ventilation. Because the entire vital capacity is rarely used, the effects are noticed only when demand for oxygen increases. © McGraw Hill LLC 105  The Effects of Aging on Organ Systems 6 Excretory System. Blood supply to the kidneys is reduced. The kidneys become smaller and less efficient at filtering wastes. Salt and water balance are difficult to maintain. The elderly become dehydrated easier than young people. Urinary incontinence increases with age. In males, an enlarged prostate gland may reduce the diameter of the urethra. © McGraw Hill LLC 106  The Effects of Aging on Organ Systems 7 Nervous System. Between the ages of 20 to 90, the brain loses weight and volume. Neuron death may be due to reduced blood flow and oxygen deficiency, not from aging itself. Loss of brain function may occur due to alterations in complex chemical reactions or increased inflammation. Animal studies suggest that reduced calorie intake may lead to fewer Alzheimer’s-like changes in the brain. © McGraw Hill LLC 107  The Effects of Aging on Organ Systems 8 Sensory Systems. Generally, more stimulation is needed for taste, smell, and hearing receptors to respond as before. About 15% of individuals over 80 suffer from anosmia (inability to smell). Potentially serious because of inability to smell smoke, gas leaks, or spoiled food. After age 50, we lose the ability to hear tones at higher frequencies. Starting at age 40, the eye lens does not accommodate as well, making it difficult to focus on near objects. © McGraw Hill LLC 108  The Effects of Aging on Organ Systems 9 Musculoskeletal System. Beginning in the 20s or 30s, but accelerating with increasing age, muscle mass decreases. Due to decreases in both the size and number of muscle fibers. Decrease of 50% from age 20 to 90. Loss of skeletal muscle mass may be slowed by exercise. © McGraw Hill LLC 109  The Effects of Aging on Organ Systems 10 Musculoskeletal System. Bones tend to shrink in size and density with age. Loss of height is common due to vertebrae compression and changes in posture. After menopause, women tend to lose bone mass more rapidly than men. Osteoporosis is a common disease in the elderly. Proper diet and exercise may slow down the progression of osteoporosis. © McGraw Hill LLC 110  The Effects of Aging on Organ Systems 11 Endocrine System. Aging of the hormonal system can affect many different organs. Some hormones increase, others decrease with age. Thyroid activity generally declines, resulting in lower basal metabolic rate. Cells become less sensitive to insulin. Human growth hormone (HGH) levels decline. © McGraw Hill LLC 111  The Effects of Aging on Organ Systems 12 Reproductive System. Testosterone production in males falls 1% per year after age 30. This decline leads to decreased sex drive, excessive weight gain, loss of muscle mass, osteoporosis, general fatigue, and depression. Testosterone treatment is controversial. Females undergo menopause, the loss of ovarian and uterine cycles, usually between ages 45 and 55. At onset, menstruation may still occur and it is still possible to conceive. Menopause is not complete until menstruation is absent for a year. © McGraw Hill LLC 112 Because learning changes everything.® www.mheducation.com © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC.