Biology Sylvia S. Mader Michael Windelspecht Chapter 42 Animal Development and Aging Lecture Outline Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. See separate FlexArt PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes. 1

Outline 42.1 Early Developmental Stages 42.2 Developmental Processes 42.3 Human Embryonic and Fetal Development 42.4 The Aging Process 2

42.1 Early Developmental Stages Fertilization requires that sperm and egg unite to form a zygote Details of Fertilization in Humans  A human sperm cell has three parts: The head –Contains a haploid nucleus covered by acrosome containing enzymes, allowing the sperm to penetrate the egg. A middle piece –Contains ATP ‑ producing mitochondria The tail –A flagellum that allows the sperm to swim 3

Early Developmental Stages Details of Fertilization in Humans (cont.)  An egg Actually a secondary oocyte Surrounded by layers of adhering follicular cells termed the corona radiata –Nourish oocyte and follicle Surrounded by the zona pellucida –Sandwiched between the plasma membrane of the oocyte and the corona radiata 4

Early Developmental Stages Details of Fertilization in Humans (cont.)  Several hundred sperm reach the oocyte  Sperm secrete enzymes to weaken the corona radiata and bind to the zona pellucida  Acrosome releases digestive enzymes to allow the sperm to pass through the zona pellucida to the plasma membrane of the oocyte 5

Early Developmental Stages Details of Fertilization in Humans (cont.)  One sperm enters the egg Membrane depolarizes to prevent polyspermy  Fertilization membrane forms  The secondary oocyte completes meiosis  The sperm nucleus releases chromatin  A single nuclear envelope surrounds the egg and sperm pronuclei  First cell division occurs 6

Fertilization 7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. corona radiata zona pellucida oocyte plasma membrane egg pronucleus cortical granule fertilization membrane tail head acrosome sperm pronucleus microvilli of oocyte plasma membrane sperm 1. Sperm makes its way through the corona radiata. 2. Acrosomal enzymes digest a portion of zona pellucida. 3. Sperm binds to and fuses with oocyte plasma membrane. 4. Sperm nucleus enters cytoplasm of oocyte. 5. Cortical granules release enzymes; zona pellucida becomes fertilization membrane. 6. Sperm and egg pronuclei are enclosed in a nuclear envelope. © David M. Phillips/Visuals Unlimited; (Chick, p. 779): © Photodisc/Getty Images middle piece plasma membrane nucleus

Early Developmental Stages Embryonic Development  Development – all the changes that occur during the life cycle of an organism  During first stages of development, an organism is called an embryo  Following fertilization, the zygote undergoes cleavage Cleavage is cell division without growth Morula forms a blastula with a hollow blastocoel Appearance of blastula differs between organisms –In chickens the blastula resembles a layer of cells spread out over yolk –In frogs, the presence of the yolk causes uneven division, forming both an animal and vegetal pole 8

Lancelet Early Development 9 a. Zygote Morula blastocoel Blastula Late gastrula mesoderm ectoderm endoderm b. blastocoel archenteron Cleavage is occurring. Gastrulation Is occurring. Early gastrula ectoderm endoderm blastopore (a): © William Jorgensen/Visuals Unlimited Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Chick Blastula 10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. blastocoel yolk Chick blastula (cross section) (chick): © Photodisc/Getty RF

Early Developmental Stages Tissue Stages of Development  Gastrulation – formation of a gastrula Germ layer formation and differentiation –Ectoderm – outer layer –Mesoderm – middle layer of cells –Endoderm – inner layer Blastopore –Pore created by the inward folding of cells –Eventually becomes the anus 11

Embryonic Germ Layers 12

Comparative Development of Mesoderm 13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. archenteron mesoderm primitive streak archenteron mesoderm archenteron mesoderm b. Frog late gastrula c. Chick late gastrula ectodermyolkyolk plugendoderm longitudinal section a. Lancelet late gastrula ectodermendoderm cross section ectodermendoderm

Early Developmental Stages Organ Stages of Development  Nervous system Develops from midline ectoderm located just above the notochord –Notochord = dorsal supporting rod Thickening of neural plate is seen along dorsal surface of the embryo Neural folds develop on either side of neural groove Neural grove becomes the neural tube 14

Development of Neural Tube and Coelom in a Frog Embryo 15 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. presumptive notochord neural plate notochord0 notochord neural groove yolk a. b. c. d. gut coelom neural tube ectoderm mesoderm endoderm archenteron coelom gut b: Courtesy Kathryn Tosney

Vertebrate Embryo, Cross Section 16 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ectodermmesodermendoderm neural tube somite notochord gut coelom

42.2 Developmental Processes Development requires:  Growth  Cellular Differentiation Cells become specialized in structure and function  Morphogenesis Produces the shape and form of the body Includes pattern formation –Arrangement of tissues and organs within the body –Involves apoptosis »Programmed cell death 17

Developmental Processes Cellular Differentiation  The zygote is totipotent Has the ability to generate the entire organism  Adult body cells lose their totipotency, but do not lose genetic information  Each contains all the instructions needed by any other specialized cell in the body 18

Developmental Processes Cellular Differentiation (continued)  Cytoplasmic Segregation Maternal determinants are parceled out during mitosis Cytoplasm of a frog’s egg is not uniform 19

Cytoplasmic Segregation 20 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cytoplasmic segregation maternal determinants

Developmental Processes Cellular Differentiation (continued)  Induction and Frog Experiments Induction –The ability of one embryonic tissue to influence the development of another tissue Molecular concentration gradients may act as chemical signals to induce germ layer differentiation Developmental path of cells is influenced by neighboring cells 21

Cytoplasmic Influence on Development 22 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. animal pole Dorsal Posterior vegetal pole Dorsal Anterior VentralPosterior a. Zygote of a frog is polar and has axes. plane of first division gray crescent site of sperm fusion b. Each cell receives a part of the gray crescent c. Only the cell on the left receives the gray crescent Ventral

Control of Nervous System Development 23 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Host embryo undergoes neurulation b. a. Host embryo has undergone gastrulation. ectoderm presumptive ectoderm Host embryo has undergone gastrulation. Host embryo undergoes neurulation. normal host neural plate presumptive mesoderm presumptive endoderm tissue transplant Presumptive nervous tissue is removed from a donor embryo. After removal of host tissue, donor presumptive nervous tissue is transplanted to belly region of host embryo. Due to normal induction process, a host neural plate develops. But donated tissue is not induced to develop into a neural normal host neural plate induced neural plate Presumptive notochord tissue is removed from a donor embryo. Host develops two neural plates—one induced by host notochord tissue, the second induced by transplanted notochord tissue. Donor presumptive notochord tissue is transplanted to a host embryo. Host belly tissue (which was removed) is returned to the host.

Developmental Processes Induction in Caenorhabditis elegans  Roundworm that develops in three days  Fate maps have been developed using this organism Show the destiny of each cell as it arises  Studies with this species demonstrate that induction requires the transcriptional regulation of genes in a particular sequence 24

Development of C. elegans, a Nematode 25 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. gonad egg sperm cuticle vulva intestine nervous system pharynx gonad (8–16 divisions) cuticle (8–11 divisions) vulva (10–13 divisions) intestine (3–6 divisions) nervous system (6–8 divisions) pharynx (9–11 divisions)

Developmental Processes Morphogenesis  Process by which an animal achieves its ordered and complex body form Requires that cells associate to form tissues, which give rise to organs Pattern formation –Cells of the embryo divide and differentiate, taking up orderly positions in tissues and organs 26

Developmental Processes Morphogenesis in Drosophila melanogaster  Fruit Fly  Pattern formation Embryonic cells express genes differently in graded, periodic, and striped arrangements Anteroposterior polarity is established in the egg before fertilization Gap genes divide the anteroposterior axis into broad regions 27

Development in Drosophila, a Fruit Fly 28 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. Protein products of gap genes b. Protein products of pair-rule genes c. Protein products of segment-polarity genes (All): Courtesy Steve Paddock, Howard Hughes Medical Research Institute

Developmental Processes Homeotic Genes control pattern formation  Organization of differentiated cells into specific three-dimensional structures  In Drosophila, certain genes control whether a particular segment will bear antennae, legs, or wings Homeotic genes all contain the same particular sequence of nucleotides, the homeobox, that encodes a 60-amino-acid sequence called a homeodomain 29

Pattern Formation in Drosophila 30 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. fly chromosome Hox-2 Hox-1 Hox-3 Hox-4 fruit fly fruit fly embryo mouse a. b. mouse chromosomes mouse embryo Courtesy E.B. Lewis

42.3 Human Embryonic and Fetal Development Human gestation time - time from conception to birth - is approximately nine months  Embryonic Development - Months 1-2 Formation of major organs  Fetal Development - Months 3-9 Major organs become larger and refined 31

Human Embryonic and Fetal Development Extraembryonic Membranes  Chorion – responsible for gas exchange  Amnion – contains the protective amniotic fluid, which functions to bathe the developing embryo  Allantois – collects nitrogenous wastes  Yolk sac – provides nourishment  Presence of embryonic membranes in humans demonstrates our evolutionary relationship to reptiles 32

Extraembryonic Membranes 33 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. chorion Human Chick amnion embryo allantois yolk sac chorion amnion yolk sac embryo allantois maternal portion of placenta fetal portion of placenta umbilical cord

Human Embryonic and Fetal Development Embryonic Development  First Week Morula transformed into blastocyst Blastocyst consists of –A fluid-filled cavity –A single layer of outer cells called the trophoblast »gives rise to chorion –Inner cell mass - develops into a fetus 34

Human Embryonic and Fetal Development Embryonic Development (continued)  Second Week Implantation begins –Trophoblast secretes human chorionic gonadotropin (HCG) »Maintains corpus luteum, therefore maintaining the endometrium and preventing menstruation »Hormone that is the basis of the pregnancy test Gastrulation occurs –Inner cell mass flattened into embryonic disk –Ectoderm, mesoderm, and endoderm differentiate 35

Human Development Before Implantation 36 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. secondary oocyte single cell = zygote 2-cell stage 4-cell stage 8-cell stage 4. Morula 3. Cleavage 2. Fertilization egg nucleus sperm nucleus secondary oocyte zona pellucida corona radiata 5. Early blastocyst 1. Ovulation fimbriae ovary oviduct inner cell mass 6. Implantation early chorion (fertilization): © Don W. Fawcett/Photo Researchers,Inc.; (2-cell): © Rawlins-CMSP/GettyImages;(morula): © RBM Online/epa/Corbis; (implantation): © Bettmann/Corbis

Human Embryonic Development 37 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. amniotic cavity embryonic disk yolk sac blastocyst cavity trophoblast a. 14 days b. 18 days c. 21 days umbilical cord digestive tract allantois amnion chorion d. 25 days e. 35+ days body stalk amniotic cavity embryo yolk sac chorionic villi chorion amniotic cavity embryo yolk sac chorionic villi amniotic cavity amnion chorion chorionic villi

Human Embryonic and Fetal Development Embryonic Development (continued)  Third Week Nervous system and circulatory system appear  Fourth and Fifth Weeks Umbilical cord is fully formed Limb buds appear Head enlarges Sense organs more apparent –Discernable eyes, ears, and nose 38

Human Embryo at Beginning of Fifth Week 39 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. brain tail limb bud somite a. liver gastrointestinal tract heart limb bud brain tail limb bud b. pharyngeal pouch optic vesicle region of heart, liver umbilical vessel optic vesicle umbilical vessel pharyngeal pouch a: © Lennart Nilsson, A Child is Born, Dell Publishing

Human Embryonic and Fetal Development Embryonic Development (continued)  Sixth Through Eighth Weeks Head achieves normal relationship with the body as a neck region develops Nervous system is developed enough to permit reflex actions 40

Human Embryonic and Fetal Development The Structure and Function of the Placenta  Placenta a mammalian structure that functions in gas, nutrient, and waste exchange between embryonic and maternal cardiovascular systems. Begins formation once the embryo is fully planted 41

Human Embryonic and Fetal Development The Structure and Function of the Placenta (cont.)  Chorionic villi Project into the maternal tissues Surrounded by maternal blood sinuses The maternal and fetal blood do not mix Exchange between the fetal and maternal blood takes place across the walls of the chorionic villi –CO 2 and wastes move across from the fetus –O 2 and nutrients flow from the maternal side  By the tenth week, the placenta is fully formed 42

Anatomy of the Placenta in a Fetus at Six to Seven Months 43 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. amniotic fluid Placenta chorionic villi umbilical cord umbilical blood vessel placenta endometrium vagina umbilical cord maternal blood vessels

Human Embryonic and Fetal Development Fetal Development and Birth  Fetal development (months 3–9) involves: Extreme increase in size  The genitalia appear in the third month  A fetus soon acquires hair, eyebrows, eyelashes, and nails  A fetus at first only flexes its limbs and nods its head Later it moves its limbs vigorously A mother feels movements from the fourth month on  After 16 weeks, a fetal heartbeat is heard through a stethoscope.  A fetus born at 24 weeks may survive 44

Preventing and Testing for Birth Defects It is believed that at least 1 in 16 newborns has a birth defect Hereditary defects can sometimes be detected before birth  Amniocentesis allows the fetus to be tested for abnormalities of development;  Chorionic villi sampling allows the embryo to be tested;  During preimplantation genetic diagnosis, eggs are screened prior to in vitro fertilization 45

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. amniotic cavity a. Amniocentesis amniotic fluid and fetal cells ultrasound scanner suction tube b. Chorionic villi sampling laparoscope aspirator ovary uterus large intestine bladder c. Preimplantation genetic diagnosis Three Methods for Genetic Defect Testing Before Birth 46

Preventing and Testing for Birth Defects Have Good Health Habits  Nutritious diet  Avoid potentially harmful substances, radiation, and pathogens Avoid Alcohol, Smoking, and Drugs of Abuse  Alcohol consumption during pregnancy is a leading cause of birth defects  Many preventable birth defects are caused by cigarette smoking Avoid Certain Medications and Supplements  Even prescription drugs may cause birth defects Avoid Having X-rays  Penetrating forms of radiation such as X-rays can hinder cell division and damage DNA,  A particular concern for the rapidly dividing and differentiating cells of a fetus. 47

Human Embryonic and Fetal Development Stages of Birth  When the fetal brain matures, the hypothalamus causes the pituitary to stimulate the adrenal cortex so that androgens are released.  The placenta uses androgens as precursors for estrogens that stimulate the production of prostaglandin and oxytocin  The hormones estrogen, prostaglandin, and oxytocin all cause the uterus to contract and expel the fetus  The process of birth (parturition) has three stages: dilation of the cervix, birth of the baby, and expulsion of the placenta 48

Three Stages of Parturition 49 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ruptured amniotic sac a. First stage of birth: cervix dilates placenta b. Second stage of birth: baby emerges placenta uterus umbilical cord c. Third stage of birth: expelling afterbirth

42.4 The Aging Process The Effects of Aging on Organ Systems  Integumentary System Skin becomes thinner and less elastic leading to sagging and wrinkling of the skin Less adipose tissue in subcutaneous layer leading to tendency to be cold Sweat glands become less active leading to decreased tolerance of high temperatures Decreased number of hair follicles and reduction in number of melanocytes 50

The Aging Process The Effects of Aging on Organ Systems (cont.)  Cardiovascular System Weakening of heart muscles Decrease in maximum heart rate and increased time for heart rate and blood pressure to return to normal resting levels after stress Gradual increase in blood pressure with age, leading to hypertension 51

The Aging Process The Effects of Aging on Organ Systems (cont.)  Immune System Immune system function becomes compromised with age Reduction in size of thymus –Results in a decreased ability to generate T-cell responses to new antigens Decline in antibody responses –Reduces responses to vaccinations in elderly individuals 52

The Aging Process The Effects of Aging on Organ Systems (cont.)  Digestive System Reduced secretion of saliva leads to an increase in bacteria adhering to teeth –Causes tooth decay and periodontal disease Reduced blood flow to liver resulting in less efficient metabolism of drugs or toxins  Respiratory System Decreased elasticity of lung tissue results in reduced ventilation 53

The Aging Process The Effects of Aging on Organ Systems (cont.)  Excretory System Reduced blood supply to the kidneys Kidneys become smaller and less efficient at filtering wastes. Difficulties maintaining salt and water balance Urinary incontinence increases with age 54

The Aging Process The Effects of Aging on Organ Systems (cont.)  Nervous System Reduction in brain size and volume  Sensory Systems More stimulation needed for taste, smell, and hearing receptors to function Cataracts and other eye disorders common Presbyopia –Difficulty focusing on near objects 55

The Aging Process The Effects of Aging on Organ Systems (cont.)  Musculoskeletal System Decrease in muscle mass Reduction in size and density of bone  Endocrine System Reduced activity of thyroid gland Reduction in levels of human growth hormone 56

The Aging Process The Effects of Aging on Organ Systems (cont.)  Reproductive System Reduction in testosterone levels –Leads to decreased sex drive, excessive weight gain, loss of muscle mass, osteoporosis, fatigue, and depression Menopause –Ovaries no longer secrete estrogen and progesterone –Hot flashes »Dizziness, headaches, insomnia, sleepiness, depression caused by circulatory irregularities 57

The Aging Process Hypotheses About Why We Age  Preprogrammed Theories Aging is genetically preprogrammed –Evidence: »Longevity runs in families »Similar lifespan of identical twins »Mutations influence lifespan »Telomere reduction over time  Damage Accumulation Theories Aging involves the accumulation of damage over time –Accumulation of harmful DNA mutations –Poor diet, exposure to the sun 58