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

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