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Early Development Gametes
Egg Lecithal = Yolk
Microlecithal egg Small amount of yolk Amphioxus Eutherians
Mesolecithal egg Medium amount of yolk Amphibians
Macrolecithal egg Large amount of yolk Bird and reptiles Most fish
Isolecithal Even yolk distribution In microlecithal eggs
Telolecithal Uneven yolk distributionMacrolecithal and Mesolecithal eggs Vegetal Pole – yolk region Animal Pole – relatively yolk-free, high metabolic activity/embryo
Amniote eggs Amnion Allantoic cavity Amnionic cavity Allantois AlbuminChorion Yolk
Layers around egg Vitelline membrane Jelly Capsule Shell AlbuminCorona Radiata Zona Pellucida
Internal FertilizationApodans Urodeles Amniotes
External FertilizationFish Frogs
Cleavage & Blastula Microlecithal EggsCleavage – Mitosis divisions Blastomeres Blastocoel
Cleavage & Blastula Blastocyst in mammals Inner cell mass in mammalsTrophoblast cells in mammals
Cleavage & Blastula Mesolecithal eggs
Cleavage & Blastula Macrolecithal EggsBlastoderm Blastocoel
Gastrulation Germ layers form from which ALL future organs formNotochord forms Bilateral symmetry established
Gastrulation/Microlecithal eggsInvolution Blastopore Archenteron
Germ layers Ectoderm –outer layer Mesoderm – middle layerForms notochord Splits to form coelom Endoderm – inner layer around archenteron
Gastrulation Mesolecithal eggsEpiboly
Ectoderm Nervous System Sensory structuresNeural crest cells that become melanocytes, adrenal gland… Epidermis of skin Epithelium of mouth/nose and anus
Endoderm Lungs & Swim bladders Digestive viscera
Mesoderm Chordomesoderm becomes notochord
Mesoderm Dorsal Mesoderm = Epimere Segmented bands called somitesDivides into Dermatome Myotome Sclerotome
Mesoderm Lateral plate mesoderm = hypomereSplits into Somatic and Splanchnic layers Coelom between these layers
Hypomere Somatic Mesoderm plus Ectoderm = SomatopleureSplanchnic Mesoderm plus Endoderm = Splanchnopleure
Mesoderm Intermediate mesoderm = MesomereKidney tubules and associated ducts
Key Points Which germ layer (ectoderm, endoderm, mesoderm) gives rise to the following structures: Heart Liver Lung Biceps muscle Notochord Brain Kidney Spinal cord Skin
Gastrulation in Macrolecithal eggsDelamination Blastoderm forms upper sheet of cells called Epiblast and Lower sheet of cells called Hypoblast Epiblast becomes Ectoderm Hypoblast becomes Endoderm
Gastrulation in Macrolecithal eggsMesoderm forms by Primitive Streak Cells stream inward from posterior to anterior Gives rise to notochord
Gastrulation in macrolecithal eggsSome mesoderm is unorganized and migrates, called MESENCHYME
Gastrulation in macrolecithal eggsBody stalk Connection from body to yolk
Gastrulation in mammalBlastoderm Delamination to form hypoblast & epiblast Primitive streak forms mesoderm Notochord Mesenchyme Coelom from splitting of lateral plate mesoderm
Neurulation Dorsal hollow nerve cord Neural crest cells branch off
Organogenesis Beginning of all major organs of the body
Extraembryonic membranesFish Body stalk Yolk sac
Extraembryonic membranesAMNIOTES Yolk sac (from splanchnopleure)
Amniotes Amnion From somatopleure Amniotic Fluid
Amniotes Chorion From somatopleureFor communication with oxygen source Helps form placenta in mammals Against shell in birds
Amniotes Allantois From splanchnopleure Gas exchange in reptilesWaste receptacle in eutherians
Placenta in EutheriansExcellent waste removal & nutrient uptake Mom’s uterus plus baby’s extraembryonic membrane Attaches to baby via umbilical cord Yolk sac functions as placenta in marsupials
Today’s Objective: 2.1 The student will list the germ layers and their derivatives The student will be able to sequence the stages of animal development.
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