Somites set up central axis of body key role in segmentation of other parts of body
neural tube (brain) heart (just beating) gut 1. Need a nervous system (folds into a tube) 2. Need segments 3. Need a gut and body cavity (other tubes) How do we get from 3 cell lines to something that looks like an organism? 4th week, ventral view
The mesoderm lateral to the somites also differentiates Paraxial somites (vertebrae & associated muscles) Neural tube Intermediate (urogenital system) notochord Body wall Gut wall Circulatory system Limbs Lateral plate
Splanchnic (gut) the story is a little tricky The lateral plate mesoderm splits into two layers: somatic (body) and splanchnic (gut) Paraxial Intermediate Lateral plate Somatic (body)
Gut tube Neural tube THESE BEGIN TO FOLD AROUND THE FUTURE FRONT (VENTRAL) SIDE OF THE EMBRYO
THESE FOLD AND MEET IN THE MIDLINE, FORMING A CENTRAL BODY CAVITY (COELOM*) *pronounced “seelom” COELOM* Gut tube Neural tube Paraxial mesoderm Splanchnic mesoderm Somatic mesoderm
THE BODY CAVITY IS A USEFUL PLACE TO PUT ALL SORTS OF ORGANS…
So, now, we have basically a segmented worm THIS IS THE BASIC BODY PLAN OF CHORDATES! Central nervous system Central axis Segmented body Gut
Phylotypic stage Which is the fish, salamander, turtle, pig, dog, bird, monkey or human?
fish s ala ma nd er turtl e bir d pig dog monkey human Phylotypic stage
1. body is largely a set of folding tubes and sheets , each of which derives from three initial layers of cells REMEMBER THIS INTRODUCTORY STATEMENT? Three germ layers Tubes and sheets Simple embryo
BUT, WE HAVE: limbs hair, milk Skeletons, heads All of these novelties are modifications of basic chordate plan! (next week) mammals reptiles amphibians fish lancelets
10:00 MAC Steps ALL LEVELS WELCOME ESPECIALLY NON-RUNNERS! Come Run! SUNDAY!!!! How did evolution modify development of the basic body plan so that we got: NEXT LECTURE (Wednesday) - bones, muscles, nerves all connected - limbs - heads with big, complex brains
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- Fall '10
- Developmental Biology, Neural tube, Mesoderm, basic body plan