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
Mar 27, 2015
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
Embryology
Study of development from fertilized egg until all major organ systems are formed.
Fertilization
Sperm must penetrate gel coat of an egg.
Sperm Cells on Egg Surface
Types of Eggs
Macrolecithal MesolecithalMicrolecithal
Egg Activation
Fusion of acrosomal membrane and egg membrane
Acrosome Reaction
Stages of Egg Activation
Egg membrane wraps microvilli around sperm head
Sperm is drawn into egg cytoplasm Formation of fertilization membrane Vitelline layer lifts off of the egg Vitelline layer strengthens and thickens Cortical changes take place (gray
crescent in amphibians)
Fast Electrical Block to Multiple Fertilizations
Other changes with fertilization
Formation of animal poleFormation of vegetal pole
Cleavage
Holoblastic
Meroblastic
Primary Germ Layers
Ectoderm
Nervous tissueSkin epidermisSensory organs
EndodermGut liningDigestive glandsLining of respiratory tract
MesodermConnective tissuesExcretory structuresReproductive structuresMuscles
Echinoderm Embryology
Echinoderm – “spiny skin”
Sea stars, sea urchins, etc.
Initial CleavageEggs are microlecithalCleavage is holoblasticCleavage (2 cell, 4 cell,
etc.) initially forms the morula
Blastula FormationInterior of morula is pulled
awayForms blastocoelHollow ball = BLASTULA
(layer is one cell thick)
Gastrula formation - morphogenesis Invagination begins at vegetal pole
(blastopore – becomes the anus) Archenteron is formed – embryonic gut Embryo lengthens – forms
anterioposterior axis Coelom devlops from outpockets of
archenteron Mouth formed when gut breaks through
anterior wall
Vertebrate Embryology
All Chordates Possess
Dorsal hollow nerve tubeNotochordPharyngeal gill slitsPostanal tail
Amphibian Embryology
Initial CleavageEggs fertilized externallyAnimal pole (gray)Vegetal pole (white) – lots of
yolkCleavage forms a morula that
rests ON TOP of the vegetal pole
Gastrulation
Amphibian Gastrulation
Groove forms between gray crescent and vegetal pole
Involution occurs Cells spread from blastopore toward
animal pole Forms a “yolk plug.”
Yolk Plug
Results of Gastrulation
Cells spread from animal pole toward the dorsal lip of the blastopore – layers thin
Archenteron formation Epiboly – ectoderm spreads
over entire embryo
Mesoderm Roll over the dorsal lip of blastopore Detach from endoderm and forms
CHORDOMESODERM Spreads anteriorly Thickens along the sides of the
embryo – form SOMITES Forms body cavidy - COELOM
Somites
Neural Tube Formation
NeurulationNerual plate on dorsal
ectoderm begins to roll inward
Neural Tube Formation
Closing the Neural Fold
Avian Embryology
Structure of Avian Egg
Initial CleavageMeroblasticFormation of BLASTODERMBlastoderm begins to move and
sorts cells into two layers:–Epiblast
–Hypoblast
Initial Cleavage
GastrulationForms a primitive streak Henson’s node Eventually forms the
notochord and neural tube
Avian Egg MembranesYolk sac – holds nutients for
embryoAmnion – shock absorberChorion – gas exchangeAllantois – grows off gut, holds
waste products and gas exchange