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