Embryology of the Musculoskeletal System

Question 1

Development of the limbs begins when

Answer 1

Near the end of the 4th week

Question 2

When does the upper limb bud appear

Answer 2

Day 24

Question 3

When does the lower limb bud appear

Answer 3

Day 26

Question 4

What results in the development of the limb buds

Answer 4

Activation of mesenchymal cells in the somatic lateral mesoderm

Question 5

What genes are responsible for the formation and patterning of limbs

Answer 5

HOX genes

Question 6

How do the limb buds elongate

Answer 6

Proliferation of mesenchyme

Question 7

The upper limb bud develops opposite

Answer 7

The caudal cervical segments

Question 8

The lower limb bud develops opposite

Answer 8

The lumbar and sacral segments

Question 9

What happens at the apex of each limb bud

Answer 9

Ectoderm thickens to form an apical ectoderm ridge

Question 10

Describe the apical ectodermal ridge

Answer 10

Multi-layered epithelial structure which exerts an inductive influence on the limb mesenchyme

Question 11

Mesenchyme adjacent to the apical ectodermal consists of

Answer 11

undifferentiated rapidly proliferating cells

Question 12

Mesenchyme proximal to the apical ectodermal ridge consists of

Answer 12

Cells that differentiate into blood vessels, cartilage and bone models

Question 13

Describe the development of hand and foot plates

Answer 13

The distal ends of the limb buds flatten into paddle like hand plates and flipper like foot plates. By the end of the 6th week the mesenchyla tissue in the hand plates has condensed to form fingers and by the 7th week the same happens in the feet

Question 14

How are interdigital regions formed

Answer 14

Programmed cell death mediated by bone morphogenic proteins

Question 15

How are bone precursors developed in the limbs

Answer 15

Cartilaginous precursors of the limb bones develop by condrification within the mesoderm in the 6th weeks, primary centres of ossification appear in weeks 8-12 in response to growth factors.

Question 16

The upper limbs rotate by

Answer 16

90 degrees laterally so that the extensors are on the lateral and posterior surfaces

Question 17

The lower limbs rotate by

Answer 17

90 degrees medially so that the extensors are on the anterior surface and the big toe is medial

Question 18

During which week do peripheral nerves grow from the developing limb plexus into the mesenchyme of the limbs

Answer 18

The 5th week

Question 19

Amelia

Answer 19

Total absence of a limb

Question 20

Meromelia

Answer 20

Partial absence of a limb

Question 21

Phocomelia

Answer 21

Some long bone absence

Question 22

Micromelia

Answer 22

All parts of the limb present apart from the long bones

Question 23

Polydactyly

Answer 23

This is the presence of more than 5 digits on the hands or the feet. The extra digit is incompletely formed and lacks muscular development

Question 24

Syndactyly

Answer 24

This is either cutaneous (webbing between the digits) or osseus (fusion of digital bones

Question 25

Congenital clubfoot

Answer 25

Talipes Equinovarus is when the sole of the foot is turned medially and the foot is inverted. Causes include genetics and lack of movement in the womb

Question 26

Developmental Dysplasia of the Hip

Answer 26

this is abnormal development of the acetabulum. This occurs in 15% of infants with conegenital dislocation of the hip.