11. Embryology of the Limbs Flashcards
What is induction?
Stimulation of specific development by communication between inducing and responding tissue
What is gastrulation?
Process of establishing germ layers
What happens at the paraxial mesoderm?
Cells close to the midline form a thickened plate
What happens at the lateral plate?
Remains thin
Divides into somatic and splanchnic layers
What are somites?
Segmented series of tissue blocks on each side of neural tube in paraxial mesoderm
Send signals to induce lateral plate mesoderm to condense and grow outwards
What is the apical ectodermal ridge?
Ectoderm along apex of bud differentiates into a ridge-like thickening which is raised at the tip
Induces differentiation of underlying mesoderm
What two ways can ossification take place?
Intramembranous
Endochondrial
Describe the process of endochondrial ossification
- Chondrocytes enlarge in centre of model, matrix forms struts which are calcified
- Blood vessels enter perichondrium, inner cells differentiate to osteoblasts
- Blood vessels and stem cells into middle of calcified cartilage, eroded by multinucleated cells, primary centre of ossification is formed and spreads towards ends
- Growth in length and diameter by osteoblasts and hyaline cartilage
- Centre of epiphysis develops secondary ossification centres
- Epiphysis filled with spongy bone, ossification centres fuse
Which way does the upper limb rotate?
Laterally
Which way does the lower limb rotate?
Medially
C5 dermatome
Over deltoid
C6
Over thumb
C7
Middle finger
C8
Medial forearm
T1
Over axilla
