Post on 27-Dec-2015
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
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?
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)
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
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)