Embryology and Body Cavities

Lecture 3

Tissue Development• Zygote (fertilized egg) undergoes rapid cell

divisions called cleavage• Forms a hollow ball of cells called the

blastula

Blastula

Tissue Development Continued• The blastula

INVAGINATES (folds inward at one point)• Called Gastrulation• The opening is called

the blastopore• The center is the

primitive gut or Archenteron blastopore

Archenteron

Gastrula

Embryonic Development

Tissue Development• Protostomes-mouth forms from

blastopore–Mollusks, Annelids, Arthropods

• Deuterostomes- anus forms from blastopore–Echinodermata, Chordata

Germ Layers• Germ layers forms tissues, organs, and

systems

• 3 Types of Germ Layers1. Ectoderm2. Mesoderm3. Endoderm

3 Germ Layers1. Ectoderm- outer most layer– Gives rise to: • Epidermis (skin)• Nervous system

• 2. Mesoderm-middle layer–Gives rise to:•Muscles•Skeleton•Blood System

• Endoderm- inner most layer–Gives rise to:•Digestive Organs•Lungs•Bladder

Three Types of Organisms1. Multicellular-have no tissue layers at all–Sponges

2. Diploblastic-have only Ectoderm and Endoderm–Cnidarians (jellyfish, sea anemones)

3. Triploblastic-have all three layers–Mollusks, arthropods, echinoderms,

chordates, etc.

Benefit of Having a Body Cavity?

• Provides room for organ development• Provides more surface area for

gas exchange and nutrient absorption• Provides for storage area

Benefits Cont’d

• Can act as a hydrostatic skeleton• Allows for waste removal• Allows for increased body size

Triploblastic Organisms

• Have three Coelom (body cavity) patterns–Acoelomate–Pseudocoelomate–Coelomate

Acoelomates

• Have a solid mass of Mesoderm cells between the Endoderm and Ectoderm layers• Ex. Flatworms

Pseudocoelomates

• The cavity is not entirely lined by mesoderm• Ex. Nematode (worm)

Coelomates

• The body cavity is completely surrounded by mesoderm.• Ex. Human

Triploblastic Body Plans

Acoelomate Pseudocoelomate Coelomate