Embryology of MSK system

Question 1

Hox genes

Answer 1

Control segmentation i.e.

• type of limb that develops from a limb bud
• vertebrae

Question 2

Homeotic mutation

Answer 2

Mutation of Hox genes e.g extra vertebrae, fingers ribs

Question 3

Thoracic outlet syndrome

Answer 3

Extra cervical ribs compress arteries and nerves

Question 4

When do limb buds first appear

Answer 4

4th week of development

Appear as small projections on the lateral body wall

Question 5

What are limb buds

Answer 5

Mass of mesenchyme covered by ectoderm

At the tip of the bud, ectoderm cells divide forming an apical ectodermal ridge.

Elongation- proliferation of mesenchyme

The apical ectodermal ridge promotes growth and development

Question 6

Does the upper or lower limb develop first?

Answer 6

Upper limb

Question 7

Upper limb rotation

Answer 7

Upper limb rotates laterally (externally) - 90 degrees on its longitudinal axis

(elbow is posterior)
(extensors are lateral and posterior)

Question 8

Lower limb

Answer 8

Lower limb rotates medially (internally) - 90 degrees

Knees are anterior
extensors are anterior