Embryology

Question 1

At what week do the early stages of MSK development occur?

Answer 1

Near the end of the 4th week

Question 2

Activations of what cells and where, lead to the development of the MSK system?

Answer 2

Mesenchymal cells in the somatic lateral mesoderm

Question 3

What regulates the patterning of MSK development?

Answer 3

Homeobox genes

Question 4

At what days do the limb buds appear?

Answer 4

24 days - upper limb bud

25-26 days - lower limb bud

Question 5

HOX genes are regionally expressed in what parts of the body?

Answer 5

The limbs

Question 6

What HOX genes are involved in the development of the upper limb?

Answer 6

HOXd9-13

Question 7

How do limb buds elongate?

Answer 7

From proliferation of mesenchyme

Question 8

What part of the spine do the upper limb buds grow next to?

Answer 8

The caudal cervical segments

Question 9

What part of the spine do the lower limb buds grow next to?

Answer 9

The lower lumbar/sacral segments

Question 10

At the apex of each bud is a thickening of what surface?

Answer 10

Ectoderm

Question 11

What is the thickening of ectoderm at the apex of each limb bud called?

Answer 11

Apical ectodermal ridge (AER)

Question 12

What type of influence does the AER have on the mesenchyme of the limb buds?

Answer 12

Inductive

Question 13

Describe the cell structure of those cells adjacent to the AER

Answer 13

Consists of undifferentiated and rapidly dividing cells

Question 14

Describe the cell structure of those cells proximal to the AER

Answer 14

Differentiate into blood vessels and cartilage-bone models

Question 15

By the 6th week, the paddle like flattened mesenchyme of the hand plate does what?

Answer 15

Condenses into digital rays

Question 16

How long does it take for the foot plates to develop digital rays?

Answer 16

7 weeks

Question 17

Between weeks 4-8, the hand and foot plates undergo what process and what does this result in?

Answer 17

Apoptosis of the interdigital regions defines fingers and toes

Question 18

What happens to cartilaginous precursors to bone in the 6th week of gestation?

Answer 18

Undergo chondrification within the mesoderm

Question 19

In response to what mediators do primary bone centres appear in the 8th-12th weeks of gestation?

Answer 19

Growth factors

Question 20

Endochondral ossification occurs for what bones of the limbs?

Answer 20

All except the clavicle

Question 21

What type of ossification does the clavicle undergo?

Answer 21

Membraneous

Question 22

Describe the rotation of the upper limbs

Answer 22

Rotate 90 degrees laterally so that the extensors are on the posterior and lateral (in the case of the thumb) surfaces

Question 23

Describe the rotation of the lower limbs

Answer 23

Rotate 90 degrees medially so that the extensors are on the anterior and medial (in the case of the big toe) surfaces

Question 24

Outline the process of dermatome formation

Answer 24

In the 5th week, the primordial limb plexus (brachial and lumbosacral) invades the limb mesenchyme

Question 25

Describe the birth defect known as aemelia

Answer 25

Total absence of limbs

Question 26

Describe the birth defect known as meromelia

Answer 26

Partial absence of limbs

Question 27

Describe the birth defect known as phocomelia

Answer 27

Some long bone absence

Question 28

Describe the birth defect known as micromelia

Answer 28

Bones are present but smaller

Question 29

Describe the birth defect known as polydactyly

Answer 29

More than 5 digits on a given (or multiple) limbs. Lacks muscularity and is incompletely formed

Question 30

Describe the birth defect known as syndactyly

Answer 30

Fusion of digits

Question 31

What are the two types of syndactyly?

Answer 31

Cutaneous - simple webbing of the digits

Osseous - bone fusion

Question 32

How does osseous syndactyly occur?

Answer 32

When the notches between the digital rays don’t form (more common in foot)

Question 33

What limb birth defect occurs due to maternal thalidomide ingestion? What non-limb defects can it cause?

Answer 33

Meromelia (partial absence of bones, particularly long bones)
Intestinal atresia, cardiac anomalies

Question 34

What is the common name of Talipes Equinovarus?

Answer 34

Congenital clubfoot

Question 35

What bone is specifically affected in developmental hip dysplasia?

Answer 35

Acetabulum

Question 36

What are the associated risk factors for developmental hip dysplasia?

Answer 36

Congenital in 15% of cases

Breech birth