Limb Embryology Flashcards Preview

MSK Anatomy > Limb Embryology > Flashcards

Flashcards in Limb Embryology Deck (26):
1

What genes regulate proximodistal patterning?

Homeobox genes

2

When does the upper and lower limb bud appear?

Upper = day 24

Lower = 1-2 days later

3

HOX gene expression results from a combination of the expression of what?

(3 things)

SHH
FGF's
WNT-7a

4

What HOX genes are expressed by upper limb?

HOXd 9-13

5

Limb buds elongate by the proliferation of what?

Mesenchyme

6

The upper limb buds develop opposite what?

The lower limb buds develop opposite what?

Caudal cervical segments

Lumbar and sacral segments

7

At the apex of each limb bud the ectoderm thickens to form what?

An apical ectodermal ridge (AER)

8

What is the apical ectodermal ridge (AER)?

Multilayered epithelial structure

Exerts an inductive influence on the limb mesenchyme

The mesenchyme adjacent to the AER consists of undifferentiated rapidly proliferating cells whereas mesenchymal cells proximal to it differentaite into blood vessels and cartilage bone models

9

How do hand and foot plates develop?

Distal ends of the limb buds flatten into paddle-like hand plates and flipper like foot plates

By the end of the 6th week, mesenchymal tissue has condensed to form digital rays

During the 7th week digital rays are formed in the foot plates

10

Apoptosis is responsible for the tissue breakdown in the interdigital regions.

What is this mediated by?

Bone morphogenetic proteins

11

Cartilaginous precursors of the limb bones develop by chondrification within the mesoderm in what week?

6th week

12

primary centres of ossification appear in which weeks in response to what?

8-12th week

Response to growth factors

13

Endochondral ossification occurs for all bones of the limbs except what?

Clavicle
(membranous ossification)

14

How do the upper and lower limbs rotate?

Upper limbs rotate 90 degrees laterally so that extensors are on the lateral and posterior surfaces (and the thumb us lateral)

Lower limbs rotate 90 degrees medially so that the extensors are on the anterior surface (and the big toe is medial)

15

Peripheral nerves grow from the developing limb plexus into the mesenchyme of the limbs during which week?

5th

16

What is a total absence of limbs called?

Amelia

17

What is a partial absence of limbs called?

meromelia

18

What is it called when some long bones are absent?

Phocomelia

19

What is it called when all bones and parts are present but they are small?

Micromelia

20

What is the genotype of lobster claw foot?

Autosomal dominant

21

What is polydactyly?

What causes it?

Presence of more than 5 digits on the hands or feet

Extra digit is incompletely formed and lacks muscular development

May be inherited or teratogen indiced

22

What is syndactyly?

What are its two types?

Common birth defect of the hand or foot

Cutaneous syndactyly (simple webbing between the digits) is a common limb defect

More frequent in the foot than in the hand.

Osseous syndactyly (fusion of bones) occurs when notches between the digital rays fail to develop

23

What is club foot also known by?

Talipes Equinovarus

24

What does club foot look like?

Sole of foot is turned medially and the foot is inverted

25

What are the causes of club foot?

Multifactorial (genetic and environmental factors)

?Abnormal positioning or resticted movement of the fetus's lower limb in the utero

26

What causes congenital dislocation od the hip in 15% of infants?

Abnormal development of acetabulum