Development Of The Limbs

Question 1

During which time period of gestation do the limb buds appear?

Answer 1

The end of the 4th week

Question 2

Describe the overall structure of the limb bud

Answer 2

Made up of mesenchymal cells from the lateral mesoderm covered in ectoderm

Question 3

What is the name given to the thickened ectoderm at the apex of the limb bud?

Answer 3

Apical ectodermal ridge (AER)

Question 4

The apical ectodermal ridge (AER) is responsible for determining which axis during development of limbs?

Answer 4

Proximal to distal

Question 5

The zone of polarising activity (ZPA) forms which axis during development of limbs?

Answer 5

Anterior to posterior

Question 6

What feature is responsible for determining the dorsal to ventral axis during limb development?

Answer 6

The ectoderm

Question 7

The zone of polarising activity (ZPA) has what role during development of the limbs?

Answer 7

Signalling centre for patterning and maintaining the AER

Generation of asymmetry in the limbs

Question 8

How are digital rays produced in the hand and foot plates?

Answer 8

Condensation of the mesenchyme within the plates beginning with the border rays

Question 9

What substance forms models of the proximal bones during limb development?

Answer 9

Hyaline cartilage

Question 10

What happens between the digits in order to get rid of the tissue that is not needed?

Answer 10

Apoptosis

Question 11

As the AER regresses by apoptosis, does it remain anywhere during development of the limbs?

Answer 11

At the tips of the digital rays

Question 12

What is syndactyly?

Answer 12

Fusion of digits (either just connective tissue or bone also)

Question 13

What is polydactyly?

Answer 13

Extra digits

Question 14

What is amelia?

Answer 14

Complete absence of a limb

Question 15

What is meromelia?

Answer 15

Partial absence of one or more limb structures

Question 16

What is phocomelia?

Answer 16

Where the hands or feet are attached directly to the trunk- limbs are grossly underdeveloped or absent

Question 17

An intrinsic error in the coordination of morphogenesis during limb development is known as what?

Answer 17

Malformation

Question 18

Deformation in morphogenesis is formed by what process during limb development?

Answer 18

Constriction bands (entrapment of fatal parts in utero)

Question 19

How might disruption of morphogenesis during limb development occur?

Answer 19

Via external agents such as thalidomide or infections (HSV, rubella)

Question 20

The upper limb bud appears opposite which spinal segments?

Answer 20

Caudal cervical

Question 21

The lower limb bud appears opposite which spinal segments?

Answer 21

Sacral and spinal segments

Question 22

At what stage of gestation do digits become apparent?

Answer 22

7th-8th week

Question 23

The ventral compartment forms the ________ muscle mass compartment during limb development

Answer 23

Flexor

Question 24

The dorsal compartment forms the _________ muscle mass compartment during limb development

Answer 24

Extensor

Question 25

The upper limb rotates in which direction?

Answer 25

Laterally

Thumb moves laterally

Question 26

The lower limb rotates in which direction?

Answer 26

Medially

The big toe rotates medially

Question 27

Before rotation of the limbs how are the thumbs, palms and elbows of the upper limb placed?

Answer 27

The thumbs face up, the palms face each other and the elbows point out

Question 28

Before rotation of the limbs how are the feet and knees positioned?

Answer 28

Soles of the feet are facing one another and the knees point out