Early Development Gametes. Sperm Egg Lecithal = Yolk.
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Transcript of Early Development Gametes. Sperm Egg Lecithal = Yolk.
Early Development
Gametes
Sperm
Egg
Lecithal = Yolk
Microlecithal egg
Small amount of yolk
Amphioxus
Eutherians
Mesolecithal egg
Medium amount of yolkAmphibians
Macrolecithal egg
Large amount of yolkBird and reptilesMost fish
Isolecithal
Even yolk distributionIn microlecithal eggs
Telolecithal
Uneven yolk distributionMacrolecithal and Mesolecithal eggsVegetal Pole – yolk regionAnimal Pole – relatively yolk-free, high
metabolic activity/embryo
AmnionAmnion
Amnioniccavity
Amnioniccavity
AllantoisAllantois
AllantoiccavityAllantoiccavity
ChorionChorionYolkYolk
Amniote eggsAmniote eggs
AlbuminAlbumin
Layers around egg
Vitelline membraneJellyCapsuleShellAlbuminCorona RadiataZona Pellucida
Oviparous
Viviparous
Ovoviviparous
Fertilization
Internal Fertilization
ApodansUrodelesAmniotes
External Fertilization
FishFrogs
Zygote
Cleavage & BlastulaMicrolecithal Eggs
Cleavage – Mitosis divisions
Blastomeres
Blastocoel
Cleavage & Blastula
Blastocyst in mammalsInner cell mass in mammalsTrophoblast cells in mammals
Cleavage & BlastulaMesolecithal eggs
Cleavage & BlastulaMacrolecithal Eggs
BlastodermBlastocoel
Gastrulation
Germ layers form from which ALL future organs form
Notochord formsBilateral symmetry established
Gastrulation/Microlecithal eggs
InvolutionBlastoporeArchenteron
Germ layers
Ectoderm –outer layerMesoderm – middle layer
– Forms notochord– Splits to form coelom
Endoderm – inner layer around archenteron
GastrulationMesolecithal eggs
Epiboly
Ectoderm
Nervous SystemSensory structuresNeural crest cells that become melanocytes,
adrenal gland…Epidermis of skinEpithelium of mouth/nose and anus
Endoderm
Lungs & Swim bladdersDigestive viscera
Mesoderm
Chordomesoderm becomes notochord
Mesoderm
Dorsal Mesoderm = EpimereSegmented bands called somitesDivides into
– Dermatome– Myotome– Sclerotome
Mesoderm
Lateral plate mesoderm = hypomereSplits into Somatic and Splanchnic layersCoelom 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 eggs
DelaminationBlastoderm forms upper sheet of cells
called Epiblast andLower sheet of cells called HypoblastEpiblast becomes EctodermHypoblast becomes Endoderm
Gastrulation in Macrolecithal eggs
Mesoderm forms by Primitive StreakCells stream inward from posterior to
anteriorGives rise to notochord
Gastrulation in macrolecithal eggs
Some mesoderm is unorganized and migrates, called MESENCHYME
Gastrulation in macrolecithal eggs
Body stalkConnection from body to yolk
Gastrulation in mammal
BlastodermDelamination to form hypoblast & epiblastPrimitive streak forms mesoderm
– Notochord– Mesenchyme– Coelom from splitting of lateral plate
mesoderm
Neurulation
Dorsal hollow nerve cordNeural crest cells branch off
Organogenesis
Beginning of all major organs of the body
Extraembryonic membranes
Fish– Body stalk– Yolk sac
Amphibians
Extraembryonic membranes
AMNIOTES– Yolk sac (from splanchnopleure)
Amniotes
AmnionFrom somatopleureAmniotic Fluid
Amniotes
ChorionFrom somatopleureFor communication with oxygen sourceHelps form placenta in mammalsAgainst shell in birds
Amniotes
AllantoisFrom splanchnopleureGas exchange in reptilesWaste receptacle in eutherians
Placenta in Eutherians
Excellent waste removal & nutrient uptakeMom’s uterus plus baby’s extraembryonic
membraneAttaches to baby via umbilical cordYolk sac functions as placenta in marsupials