What kind of car are you?

“In Nature, Nothing Is Superfluous, Nothing Is Wasted” - Leonardo DaVinci

Animal Body Plans Symmetry Number of Tissue Layers Gastric Design

Asymmetry

Bilateral Symmetry

Radial Symmetry Generally found only in aquatic animals

Number of Tissue Layers Acoelomatic = generally two tissue layers (i.e. flatworms) Pseudocoelomatic = three tissue layers with fluid filled body cavity (i.e. nematodes) Coelomatic = three or more tissue layers with lined body cavity

Gastric Design PROTOSTOMES Mouth forms first Simplest animals (i.e. Porifera, Nematoda) up through Annelida May give rise to a two-way feeding system DEUTEROSTOMES Anus forms first Insects Through Mammals Ensures a one-way feeding system

How Do Organisms Develop From A Zygote Into Their Final Forms?

Determinative Embryology

Human Fertilization Fusion of ovum and sperm Generally in the ampullary region of the fallopian tube Sperm bind to corona radiata, and penetrate the zona pellucida by using acrosomal enzymes Once sperm has penetrated and delivered DNA, egg hardens outside, preventing further sperm from fertilizing (cortical reaction)

Zygote Fertilized ovum Formed by union of two haploid gametes (ovum & sperm)

Early Animal Development Cleavage = rapid mitotic divisions –Holoblastic –Meroblastic Rate of cleavage depends upon the amount of yolk in the zygote (more = slower)

Why is cleavage necessary?

Reasons For Cell Division Provide raw materials for other cells Improve their surface area to volume ratios Create an open space for cells to move into

MORULA Latin for “mulberry” Earliest stage of embryonic development Ball of blastomeres Post 16 cell stage/Days 2-4

BLASTULA / BLASTOCYST The resulting ball of cells produced by meroblastic cleavage is called a BLASTULA or BLASTOCYST DAY 5 Center of blastula is fluid-filled BLASTOCOEL

Differences In Blastula Formation In radially symmetrical animals, the blastocoel is large In bilaterally symmetrical animals, there are two, unequally sized poles –Animal –Vegetal

Morphogenesis

What is the most important organ in the human body?

GASTRULATION Blastula undergoes meroblastic cleavage (unequal divisions) at one pole As a result of these unequal divisions, one pole of the blastula begins to invaginate (‘cave in’) The opening to the invagination is called the archenteron and the cavity is called the GASTRULA

Organogenesis Some of the cells of the original blastula are now pushed inside, lining the gastrula Other cells migrate into the space previously occupied by blastocoel As a result, three tissue layers are produced –ECTODERM –ENDODERM –MESODERM

DERMAL LAYERS ECTODERM (outside): brain, spinal cord, nerves, nose, ears, eye, skin ENDODERM (inside): lining of digestive tract, pancreas, liver, lungs MESODERM (middle): skeleton, muscle, gonads, kidneys

DIFFERENTIATION Changes that result in the formation of specialized organs or structures Example: A second invagination of the ectoderm creates the neural tube (i.e. spinal cord and column)