1. Fertilization Fertilization activates the egg
Activation of the egg triggers embryonic development

2. Acrosomal Reaction
The acrosomal reaction occurs in echinoderms Ex. sea urchins
Receptors on the vitelline egg layer are specific
The reaction is the fast block to polyspermy
A depolarization of the membrane stops other sperm from penetrating

3. The acrosomal and cortical reactions during sea urchin fertilization

4. Timeline for the fertilization of sea urchin eggs

5. Activation of The Egg
Increase in calcium also triggers increase in metabolic reaction in the egg
Artificial activation of egg can occur by injecting calcium ions

6. A wave of Ca2+ release during the cortical reaction

7. Mammalian Fertilization
Most mammals show internal fertilization
Sperm has to reach zona pellucida by penetrating follicle cells
An acrosomal reaction occurs and sperm cell enters egg
Zona pellucida hardens which blocks polyspermy
Centrosomes originate from sperm cell
Chromosomes share a common spindle during first mitotic division

8. Fertilization in Mammals

9. Early Embryonic Development
6 days
2 weeks

10. Figure 47.6 Cleavage in an echinoderm (sea urchin) embryo

11. Cross Section of a Frog Blastula

12. Cleavage Fast mitotic divisions without G1 and G2 phases
Results in smaller blastomeres
Polar planes of division occur with animal and vegetal poles
Holoblastic cleavage is complete division of eggs with little yolk ex: frogs
Meroblastic = incomplete division with moderate amt of yolk ex: birds

13. Gastrulation in a Frog Embryo

14. Body Symmetry
Exhibit
cephalization

15. Organisms without body cavities are considered acoelomates
Body covering
(from ectoderm)
Tissue-
filled region
(from
mesoderm)
Digestive tract
(from endoderm)
Acoelomate. Acoelomates such as flatworms lack a body cavity between the digestive tract and outer body wall.
(c)
Figure 32.8c

16. A pseudocoelom
Is a body cavity derived from the blastocoel, rather than from mesoderm
Pseudocoelom
Muscle layer
(from
mesoderm)
Body covering
(from ectoderm)
Digestive tract
Pseudocoelomate. Pseudocoelomates such as nematodes have a body cavity only partially lined by tissue derived from mesoderm.
(b)
Figure 32.8b

17. A true body cavity is called a coelom and is derived from mesoderm; these animals
are called coelomates
Figure 32.8a
Coelom
Body covering
(from ectoderm)
Digestive tract
(from endoderm)
Tissue layer
lining coelom
and suspending
internal organs
(from mesoderm)
Coelomate. Coelomates such as annelids have a true coelom, a body cavity completely lined by tissue derived from mesoderm.
(a)

18. Cleavage in a Frog Embryo

19. Sea urchin development, from single cell to larva

20. The Establishment of the Body Axes and the First Cleavage Plane in an Amphibian
Becomes Posterior End
Becomes
Dorsal Side
Becomes
Anterior End

21. Many different structures are derived from the three embryonic germ layers during organogenesis
Figure 47.16
ECTODERM
MESODERM
ENDODERM
• Epidermis of skin and its derivatives (including sweat glands, hair follicles)
• Epithelial lining of mouth and rectum
• Sense receptors in epidermis
• Cornea and lens of eye
• Nervous system
• Adrenal medulla
• Tooth enamel
• Epithelium or pineal and pituitary glands
• Notochord
• Skeletal system
• Muscular system
• Muscular layer of
stomach, intestine, etc.
• Excretory system
• Circulatory and lymphatic systems
• Reproductive system (except germ cells)
• Dermis of skin
• Lining of body cavity
• Adrenal cortex
• Epithelial lining of digestive tract
• Epithelial lining of respiratory system
• Lining of urethra, urinary bladder, and reproductive system
• Liver
• Pancreas
• Thymus
• Thyroid and parathyroid glands

23. Organogenesis
Folding, splitting and clustering of cells begins organogenesis
Ectoderm rolls into neural tube
Mesodermal blocks form somites along axis of notochord:
Gives rise to vertebrae and muscles of backbone
Neural plate folds into the neural tube and becomes central nervous system

24. Chorion - gas exchange and waste storage, lines the egg shell
Allantois – gas exchange and waste storage connects embryo to chorion
Yolk sac – food storage vitelline vessels embed into the yolk
Amnion – protective fluid filled sac
                                                                                

27. Human Embryo
Brain
Heart

28. Figure 47.11 Organogenesis in a frog embryo

29. Figure 47.12 Cleavage, gastrulation, and early organogenesis in a chick embryo

30. Organogenesis in a chick embryo
About
56 Hours
Old
Eye
Forebrain
Heart
Blood
Vessels
Somites
Neural
Tube

31. Figure 47.14 The development of extraembryonic membranes in a chick

32. Figure 47.15 Early development of a human embryo and its extraembryonic membranes

33. 24 Hour Chick Embryo

34. 48 Hour Chick Embryo

35. 72 Hour Chick Embryo

36. http://www. bioscience. drexel

37. Figure 32.7 A comparison of early development in protostomes and deuterostomes