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General Embryology 6/1/12

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Embryology helpful because
a tool for anatomy. There are common developmental schemes, nearly all of modern clinical research is based on non human animal models.
Haekels law
ontogeny recapitulates phylogeny. Growth from a zygote to a multicellular adult mimics evolution.
Embryos do not evolve so this doesn't work well
Von Baer's Law
Each stage of embryologic development resembles the embryos of phylogenetically related species.
The closer the relationship the longer the resemblence is in development
Fertilization happens in the
ampulla
Stages of development
1.) Zygote
2.Morula
3. Blastocyst
4.Bilaminar Germ Disk (Still Technically a Blastocyst)
5. Embryo
5a. Gastrula
5b. Trilaminar Germ Disk
5c. Neurula
6.Fetus
7.Bill, or George, or Henry, or anything but Sue!
amnion
the watery sac that the embryo develops into
yolk sac
food stuffs live off of if you were an egg developing critter
lining of the sac develops into the germ cells of the next generation
ectoderm
everything you see on the outside of a person and the nervous system
mesoderm basic
muscle, blood, bone
endoderm
linings of inner tube-lungs, stomach, small and large intestine, liver, pancreas
neuralation
ectoderm surface folds in on itself and forms the neural tube
spina bifida
failed closure of a caudal neuropore (relatively benign condition sometimes hair above butt. Can be insignificant and can be life threatening
meningomyelocele
when the entire CNS is exposed with spina bifida
anencephaly
failed closure of the rostral end of the neural pore
Lateral plate mesoderm
most distant from the notochord
develops into the body wall and limb skeletons, smooth muscle of the gut, and coelomic cavity
Intermediate mesoderm
develops into the urogenital system (kidneys and gonads)
Paraxial mesoderm
either side of the notochord-gives rise to the somites
Somite
1.) with completion of neurulation each somite pair becomes associated with the mixed spinal nerve that stems off the neural tube
2.) Every structure from that somie recieves innervation from that spinal level
3.) enlargements of paraxial mesoderm
what is significant about timing of somites
they develop and first appera on the cranial end of the embryo so by the time the final somites appear on the tail end the first somites have already differentiated into other structures
Somites first differentiate into
sclerotomes and dermomyotomes
dermomyotome differentiates into
dermatome and myotome
Dermatome (sensory component of the skin)
myotome (most of the voluntary musculature of the body)-motor problems
Cervical region transverse element
posterior costal bar (epaxial)
cervical region costal element
costal lamella and anterior costal bar
Thoracic transverse element
transverse process
Thoracic costal element
ribs
Lumbar transverse element
acessory process
Lumbar costal element
transverse process
Two methods of bone formation
Mebranous osscification and endochondral ossification
mesenchyme
generic name for disorganized web of unspecialized connective tissue
Membranous ossification
1.) starts with a mesenchymal model that transforms directly into bone
2.) More common in flat bones (skull frontal etc)
3.) creates very dense bone
4.) Adult mechanism of bone repair
Endochondral ossification
1.) Starts with a mesenchymal model
2.) Gradually this is replaced by cartilage which is usually hyline
3.) Associated more with long bones
4.) normal consequence of vascularization of cartilage
5.) Can be a pathological process (bone spurs)
Hyaline cartilage
most common type, has no fibers which are visible at the light microscope level
Fibrocartilage
contains large amounts of collagen fibers and is an important structural cartilage (intervertebral disks)
Elastic cartilage
contains large amounts of elastin, and is thus capable of being stretched and distorted and will regain its shape (ears and sides of nose)
Periosteum
"the outside lining"
Compact bone
solid structure associated with the shaft or ends (typically remodeled with osteons)
woven bone
typically young compact bone that has not yet developed in haversian systems
trabecular (spongy bone)
series of bone beams found near ends of bone
medullary cavity
the inside space with marrow
Immovable joints
favors stability of structure. movement occurs only during extreme stress or in special physiolocial circumstances
Highly moveable joints
favors free movement between the bones. Stability occurs through restrictive ligaments or muscular action.
slightly moveable joints
compromise between the movement and stability. Movement generally occurs only over small and specialized range
Two joint categories
synarthroses (solid joints) and diarthroses (cavitated joints)
Synarthroses
Osseous joints (bone on bone), fibrous joints (two bones with ligament linking them togethers), Cartilaginous joints
Diarthroses
synovial joints
Synovial joints (things always present)
1.) Capsular ligaments
2.) Articular cavity
3.) Articular (hyaline) cartilage
4.) Synovium (synovial fluid)
Synovial sometimes present
1.) Intrinsic ligaments
2.) Tendons
3.) Fat pads
4.) Fibrocartilaginous disks
5.) Bursae
Ways in which a bone can move relative to another
Translation and spin
Translation
Anterior/posterior
Superior/inferior
medial/lateral
Spin
Bone spins along vertical axis-rotation
Medial-lateral axis-Flexion/extension
anterior-posterior directed axis-abduction/adduction
Disk Herniation Least likely
to go through the posterior side because of the posterior longitudinal ligament
Disk herniation another unlikely
anterior-unlikely
most likely disk herniation
dorso-laterally can encroach on the dorsal root ganglion creating a dermatomal pain pattern