1. 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

2. Embryology
Study of development from fertilized egg until all major organ systems are formed.

3. Sperm must penetrate gel coat of an egg.
Fertilization
Sperm must penetrate gel coat of an egg.

4. Sperm Cells on Egg Surface

5. Types of Eggs
Macrolecithal
Mesolecithal
Microlecithal

6. Fusion of acrosomal membrane and egg membrane
Egg Activation
Fusion of acrosomal membrane and egg membrane

7. Acrosome Reaction

8. 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)

9. Fast Electrical Block to Multiple Fertilizations

10. Other changes with fertilization
Formation of animal pole
Formation of vegetal pole

11. Holoblastic Meroblastic
Cleavage
Holoblastic
Meroblastic

12. Primary Germ Layers

13. Ectoderm
Nervous tissue
Skin epidermis
Sensory organs

14. Endoderm
Gut lining
Digestive glands
Lining of respiratory tract

15. Mesoderm Connective tissues Excretory structures
Reproductive structures
Muscles

16. Echinoderm Embryology
Echinoderm – “spiny skin”
Sea stars, sea urchins, etc.

17. Initial Cleavage Eggs are microlecithal Cleavage is holoblastic
Cleavage (2 cell, 4 cell, etc.) initially forms the morula

18. Blastula Formation Interior of morula is pulled away Forms blastocoel
Hollow ball = BLASTULA (layer is one cell thick)

19. 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

20. Vertebrate Embryology

21. All Chordates Possess Dorsal hollow nerve tube Notochord
Pharyngeal gill slits
Postanal tail

22. Amphibian Embryology

23. Initial Cleavage Eggs fertilized externally Animal pole (gray)
Vegetal pole (white) – lots of yolk
Cleavage forms a morula that rests ON TOP of the vegetal pole

24. Gastrulation

25. Amphibian Gastrulation
Groove forms between gray crescent and vegetal pole
Involution occurs
Cells spread from blastopore toward animal pole
Forms a “yolk plug.”

26. Yolk Plug

27. 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

28. 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

29. Somites

30. Neural Tube Formation Neurulation
Nerual plate on dorsal ectoderm begins to roll inward

31. Neural Tube Formation

32. Closing the Neural Fold

33. Avian Embryology

34. Structure of Avian Egg

35. Initial Cleavage Meroblastic Formation of BLASTODERM
Blastoderm begins to move and sorts cells into two layers:
Epiblast
Hypoblast

36. Initial Cleavage

37. Gastrulation Forms a primitive streak Henson’s node
Eventually forms the notochord and neural tube

38. Avian Egg Membranes Yolk sac – holds nutients for embryo
Amnion – shock absorber
Chorion – gas exchange
Allantois – grows off gut, holds waste products and gas exchange