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ANIMAL DEVELOPMENT CH 47 FERTILIZATION THROUGH ORGANOGENESIS 1 Slide 2 STAGES OF HUMAN DEVELOPMENT 1.Fertilization 1.Zona pellucida 2.First cell division 2.Cleavage 1.Blastomere 2.Holoblastic cleavage 3.Meroblastic cleavage 4.regulation 3.Morophogenesis 1.Gastrulation 2.Organogenesis 2 Slide 3 FERTILIZATION Female secretions increase sperm motility and change structure to cause fertilization potential (capacitation) Moist environment necessary for sperm First six hours 3 Slide 4 FERTILIZATION Zona pellucida contain receptor cite and acrosomal reaction which binds sperm to egg Changes cause slow polyspermy to prevent additional sperm from entering egg No fast polyspermy reactions in mammals 4 Slide 5 FIGURE 47.5 Zona pellucida Follicle cell Sperm basal body Sperm nucleus Cortical granules 5 Slide 6 FERTILIZATION First Cell Division Mitosis forms true nuclei in daughter cells 12-36 hours after sperm bonding Each cell is now a blastomere http://www.hhmi.org/biointeractive/human-embryonic-HHMI embryonic developmentHHMI embryonic development 6 Slide 7 CLEAVAGE Rapid cell division with almost continuous S and M phases of cell cycle Little or no protein synthesis (G 1 or G 2 ) Blastula- Hollow ball of cells form with blastocoel cavity 7 Slide 8 FIGURE 47.6 (a) Fertilized egg (b) Four-cell stage (c) Early blastula (d) Later blastula 50 m 8 Slide 9 CLEAVAGE In frogs and mammals is holoblastic holo means complete Humans have 3 divisions in first three days with little yolk forming Birds and reptiles cleavage is meroblastic (incomplete) to get extensive yolk formation The ends of the blastula are called the animal pole and vegetal pole Gray crescent is the area on the opposite side from sperm binding 9 Slide 10 FIGURE 47.7 Zygote 2-cell stage forming 4-cell stage forming 8-cell stage Vegetal pole Blastula (cross section) Gray crescent Animal pole Blastocoel 0.25 mm 8-cell stage (viewed from the animal pole) Blastula (at least 128 cells) 10 Slide 11 REGULATION OF CLEAVAGE The total mass of the structure does not change from zygote to blastula, the cells just get smaller Cells divide until the ratio of material in each nucleus to cytoplasm is sufficiently large Small cells balance the amount of DNA to mRNA for protein synthesis (think surface are to volume ratio) 11 Slide 12 MORPHOGENESIS Transformation of embryo orientation and shape Important is the cell shape, position and survival Two important phases: 1.Gastrulation- establishment of cell layers 2.Organogenesis- formation of organs 12 Slide 13 MORPHOGENESIS: GASTRULATION During gastrulation there is a mass movement of cells which results in the blastula becoming a gastrula Three germ layers develop ectoderm- outside layer mesoderm- middle layer endoderm- inside layer Some organisms (cniderians) do not have a mesoderm HHMI Differentiation and Cell Fate http://www.hhmi.org/biointeractive/differentiation-and-fate- cells 13 Slide 14 FIGURE 47.8 ECTODERM (outer layer of embryo) MESODERM (middle layer of embryo) ENDODERM (inner layer of embryo) Epidermis of skin and its derivatives (including sweat glands, hair follicles) Epithelial lining of digestive tract and associated organs (liver, pancreas) Epithelial lining of respiratory, excretory, and reproductive tracts and ducts Germ cells Jaws and teeth Pituitary gland, adrenal medulla Nervous and sensory systems Skeletal and muscular systems Circulatory and lymphatic systems Excretory and reproductive systems (except germ cells) Dermis of skin Adrenal cortex Thymus, thyroid, and parathyroid glands 14 Slide 15 FIGURE 47.9 Animal pole Blastocoel Mesenchyme cells Vegetal plate Vegetal pole Blastocoel Filopodia Mesenchyme cells Blastopore Archenteron 50 m Ectoderm Mouth Mesenchyme (mesoderm forms future skeleton) Blastopore Blastocoel Archenteron Digestive tube (endoderm) Anus (from blastopore) Key Future ectoderm Future mesoderm Future endoderm Gastrulation in Sea Urchin 15 Slide 16 FIGURE 47.10 Key Future ectoderm Future mesoderm Future endoderm SURFACE VIEW CROSS SECTION Animal pole Vegetal pole Early gastrula Blastocoel Dorsal lip of blasto- pore Blastopore Dorsal lip of blastopore Blastocoel shrinking Archenteron Blastocoel remnant Ectoderm Mesoderm Endoderm Blastopore Yolk plug Blastopore Late gastrula 321 Gastrulation in Frog 16 Slide 17 FIGURE 47.11 Future ectoderm Migrating cells (mesoderm) Blastocoel Epiblast YOLK Endoderm Hypoblast Primitive streak Fertilized egg Primitive streak Embryo Yolk Gastrulation in Chick 17 Slide 18 FIGURE 47.12 Blastocyst reaches uterus. 1234 Blastocyst implants (7 days after fertilization). Extraembryonic membranes start to form (1011 days), and gastrulation begins (13 days). Gastrulation has produced a three-layered embryo with four extraembryonic membranes. Uterus Maternal blood vessel Endometrial epithelium (uterine lining) Inner cell mass Trophoblast Blastocoel Expanding region of trophoblast Epiblast Hypoblast Trophoblast Expanding region of trophoblast Amniotic cavity Epiblast Hypoblast Yolk sac (from hypoblast) Extraembryonic mesoderm cells (from epiblast) Chorion (from trophoblast) Amnion Chorion Ectoderm Mesoderm Endoderm Yolk sac Extraembryonic mesoderm Allantois Gastrulation in Human 18 Slide 19 MORPHOGENESIS: GASTRULATION IN HUMANS 1. Blastocyst first 6 days Fertilization occurs in the oviduct Inner cell mass becomes the embryo which is the source for stem cells Little yolk (stored nutrients) Blastocyst reaches uterus. Inner cell mass 19 Slide 20 MORPHOGENESIS: GASTRULATION IN HUMANS 2. Trophoblast 7 days after fertilization Outer epithelium secretes enzymes for implantation which allows for blood to surround trophoblast Epiblast-upper layer becomes the embryo Hypoblast- lower layer Maternal blood vessel 20 Slide 21 MORPHOGENESIS: GASTRULATION IN HUMANS 3. Extraembryonic membranes 10-11 days Formed by embryo Enclose special structures outside the embryo Gastrulation begins day 13 when implantation is complete Cell migration occurs as cells move inward from epiblast through primitive streak to form mesoderm and endoderm Chick gastrulation 21 Slide 22 FIGURE 47.12C Extraembryonic membranes start to form (1011 days), and gastrulation begins (13 days). Expanding region of trophoblast Amniotic cavity Epiblast Hypoblast Yolk sac (from hypoblast) Extraembryonic mesoderm cells (from epiblast) Chorion (from trophoblast) 3 22 Slide 23 MORPHOGENESIS: GASTRULATION IN HUMANS 4. End of gastrulation Three germ layers are formed Extraembryonic layers from placenta These layers are an evolutionary necessity in land (dry) environments 23 Slide 24 FIGURE 47.12D Gastrulation has produced a three-layered embryo with four extraembryonic membranes. Amnion Chorion Ectoderm Mesoderm Endoderm Yolk sac Extraembryonic mesoderm Allantois 4 24 Slide 25 ORGANOGENESIS More localized changes Research brainintestine Spinal cordliver Bones (or specific)Muscles (or specific) skineyes heartears 25 HHMI