Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Biology Sylvia S. Mader Michael Windelspecht Chapter 42 Animal Development and Aging Lecture Outline See separate FlexArt PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes. 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. microvilli of oocyte plasma membrane 2. Acrosomal enzymes digest a portion of zona pellucida. tail 1. Sperm makes its way through the corona radiata. 3. Sperm binds to and fuses with oocyte plasma membrane. sperm 4. Sperm nucleus enters cytoplasm of oocyte. corona radiata plasma membrane nucleus middle piece 5. Cortical granules release enzymes; zona pellucida becomes fertilization membrane. head acrosome fertilization membrane cortical granule sperm pronucleus 6. Sperm and egg pronuclei are enclosed in a nuclear envelope. oocyte plasma membrane zona pellucida egg pronucleus © David M. Phillips/Visuals Unlimited; (Chick, p. 779): © Photodisc/Getty Images 7 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. Zygote Late gastrula mesoderm Morula Cleavage is occurring. blastocoel endoderm ectoderm Gastrulation Is occurring. Early gastrula Blastula ectoderm endoderm blastopore b. archenteron blastocoel (a): © William Jorgensen/Visuals Unlimited 9 Chick Blastula Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chick blastula (cross section) blastocoel yolk (chick): © Photodisc/Getty RF 10 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. archenteron ectoderm mesoderm endoderm cross section a. Lancelet late gastrula archenteron mesoderm ectoderm yolk plug endoderm longitudinal section b. Frog late gastrula archenteron primitive streak mesoderm ectoderm yolk endoderm cross section c. Chick late gastrula 13 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. presumptive notochord neural plate neural groove ectoderm coelom mesoderm gut gut endoderm notochord archenteron a. neural tube notochord0 coelom b. yolk c. d. b: Courtesy Kathryn Tosney 15 Vertebrate Embryo, Cross Section Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. neural tube somite notochord gut coelom ectoderm mesoderm endoderm 16 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 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 20 Development of C. elegans, a Nematode Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. egg gonad (8–16 divisions) cuticle (8–11 divisions) gonad vulva (10–13 divisions) cuticle egg intestine (3–6 divisions) nervous system (6–8 divisions) vulva sperm intestine nervous system pharynx (9–11 divisions) pharynx 21 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 22 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 23 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 24 Pattern Formation in Drosophila Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. Hox-2 Hox-1 mouse chromosomes Hox-3 Hox-4 fly chromosome mouse embryo b. fruit fly embryo mouse fruit fly Courtesy E.B. Lewis 25 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 26 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 27 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 28 Human Embryonic Development Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. amniotic cavity embryonic disk yolk sac blastocyst cavity trophoblast a. 14 days amniotic cavity embryo yolk sac chorionic villi chorion b. 18 days body stalk amniotic cavity embryo allantois yolk sac chorionic villi c. 21 days chorion amniotic cavity allantois yolk sac amnion chorionic villi d. 25 days amniotic cavity chorion digestive tract chorionic villi amnion umbilical cord e. 35+ days 29 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 30 Human Embryo at Beginning of Fifth Week Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. tail brain brain optic vesicle optic vesicle tail pharyngeal pouch pharyngeal pouch heart region of heart, liver liver limb bud limb bud umbilical vessel umbilical vessel a. somite b. gastrointestinal tract limb bud a: © Lennart Nilsson, A Child is Born, Dell Publishing 31 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 32 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 33 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 – CO2 and wastes move across from the fetus – O2 and nutrients flow from the maternal side By the tenth week, the placenta is fully formed 34 Anatomy of the Placenta in a Fetus at Six to Seven Months Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. amniotic fluid placenta umbilical cord endometrium vagina umbilical cord umbilical blood vessel chorionic villi maternal blood vessels Placenta 35 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 36 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 37