Limb Development

Question 1

For the upper limb, describe Prexial and Postaxial

Answer 1

Preaxial is thumb and radius

Postaxial is pinky and ulna

Question 2

What week do limb buds begin forming?

Answer 2

Week 4

Question 3

What week do digits begin forming?

Answer 3

Week 8

Question 4

Primary ossification centers form during which week?

Answer 4

Week 12

Question 5

Muscles of limbs come from what?

Cartilage of the limbs and connective tissue come from what?

Answer 5

Somite mesoderm

Somatic lateral plate mesoderm

Question 6

In the limb, the mesoderm releases what factor to stimualte the surface ectoderm to induce the formation of the Apical Ectodermal Ridge?

What does the AER give off?

Answer 6

FGF10

Limb bud

Question 7

As the Apocal Ectodermal ridge forms it grows in what direction?

Answer 7

Proximally to Distally

Question 8

What is the stylopod?

Answer 8

Humerus

Femur

Question 9

What is the zeugopod?

Answer 9

Radius and Ulna

Tibia and Fibula

Question 10

What do autopods become?

Answer 10

Carpels, Metacarpals, Digits

Tarsals, Metatarsals, Digits

Question 11

What week do hand and foot plates appear?

What week do chondrification centers appear?

Answer 11

Week 5

Question 12

Digital rays of the hands, and the entire limb skeleton (cartilagenous) appears at what week?

Answer 12

Week 6

Question 13

What week do the digital rays of the feet, and osteogenesis of long bones begin?

Answer 13

Week 7

Question 14

What week does rotation of the limbs occur?

Answer 14

Week 7

Question 15

What week do seperate digits form through apoptosis?

What signalling factor is responsible for this digital apoptosis?

Answer 15

Week 8

BMP

Question 16

Why is it that upper limbs form before lower limbs?

Answer 16

Blood supply is being shunted to the brain, and upper limbs are closer to this supply (i.e. more nutrients)

Question 17

Describe the direction of rotation of limbs that occurs during Week 7?

Upper Limbs vs Lower Limbs

Answer 17

Upper limbs rotate 90 degrees Laterally

Lower limbs rotate 90 degrees Medially

Question 18

Nerves start innervating the developing muscles at what week?

Answer 18

Week 5

Question 19

Muscles of the limbs are derived from what portion of the somites?

A. Ventrolateral

B. Ventromedial

C. Dorsolateral

D. Dorsomedial

Answer 19

Dorsolateral

Question 20

Motor axons from the spinal cord enter the limb buds during the 5th week, and are derived from what?

Answer 20

Neuralectoderm

Question 21

Sensory neurons come from ________ and use ________ as a guidance.

Answer 21

Sensory neurons come from neural crest and use motor axons as a guidance.

Question 22

At week 5 upper and lower limbs start growing out in what direction?

Answer 22

Laterally and caudally

(out and down)

Question 23

At week 6, upper and lower limbs bend in what direction?

Answer 23

Anteriorly

Question 24

Is Barber pole rotation is seen in the upper or lower limb?

Answer 24

Lower limb

Question 25

What artery comes off the dorsal aorta and supplies the upper limb buds? What artery does it become within the limb bud?

Answer 25

**Intersegmental arteries** from the dorsal aorta Becomes the **primary axial artery**

Question 26

The primary axial artery in the upper limb later becomes what structure? The primary axial artey of the lower limb becomes what structure?

Answer 26

Upper limb: brachial artery Lower limb: deep artery of the thigh

Question 27

What is the most common musculoskeletal defect? What is the presentation

Answer 27

Club foot or Talipes Equinovarus Sole of foot is turned medially with foot inverted

Question 28

Which of the following is true in Developmental Hip Dysplasia? A. More common in females than males B. Caused by under development of acetabulum of the hip bone C. Caused by generalized joint laxity D. All of the above

Answer 28

All of the above A. More common in females than males B. Caused by under development of acetabulum of the hip bone C. Caused by generalized joint laxity

Question 29

Positioning and shape of the limbs is regulated by turning what signalling molecule on and off?

Answer 29

Hox genes

Question 30

Proximal to distal growth and patterning of the limbs is determined by what? Describe the signaling cycle that occurs

Answer 30

Apical Ectodermal Ridge FGF10 released by mesenchyme to AER AER release of FGF-8 and FGF-4 to mesoderm *this is how we get the stylopod, zeugopod, and autopods*

Question 31

Dorso-ventral patterning also involves the AER, but instead two other signalling factors specific to dorsal or ventral side. What is the signalling factor for the dorsal surface, and what is the signalling factor for the ventral surface?

Answer 31

VEntral surface: **BMPs** Dorsal Surface: **Wnt7**

Question 32

Anterior (preaxial) and posterior (post-axial) patterning of the limb is established by what structure? What side of the limb does this structure work on? What signalling factors are involved?

Answer 32

**Zone of Polarizing Activity** works on the **Posterior** side and releases **Shh** and **retinoic acid**

Question 33

Loss of ZPA would result in which of the following? A. Additional posterior elements (polydactyly) B. Loss of posterior elements C. Duplication of posterior elements (little fingers on both sides of the thumb)

Answer 33

Loss of posterior elements

Question 34

Upregulation of ZPA signals retionoic acid and Shh results in what? A. Additional posterior elements (polydactyly) B. Loss of posterior elements C. Duplication of posterior elements (little fingers on both sides of the thumb)

Answer 34

Additional posterior elements (polydactyly)

Question 35

T/F: Posterior elements like little finger and ulna are formed prior to anterior elements like thumb and radisu

Answer 35

True

Question 36

What is the mechanism of this disease? What week would this happen?

Answer 36

Upregulation of the ZPA Week 6 (formation of the digital rays of the hand)

Question 37

What is the mechanism of this disease? What week does this occur?

Answer 37

Duplication of ZPA Week 7 (formation of digital rays of foot plate)

Question 38

Shown below are two defects on the left structure. What is the name of both abnormalities? What is the cause of the one specific to this lecture? When does this issue occur?

Answer 38

Syndactyly: problem of BMP regulation Week 8 Brachydactyly

Question 39

Pictured below is a form of miromelia, called Phocomelia where hands/feet attach close to the body. What is the mechanism of this abnormality? In what week does it occur

Answer 39

Problem with FGF signalling and the Apical Ectodermal Ridge Week 4 - Week 8 *Happens between Week 4-week 8 because proximal to distal growth occurs during this time*

Question 40

What is the disease pictured below? In what week does this abnormality develop?

Answer 40

Amelia Week 4: a limb bud wasn't even developed for upper limbs problem with Apical ectodermal ridge

Question 41

What is the name of the abnormality pictured below? What is the mechanism of this abnormality?

Answer 41

Ectodactyly or Forked Hand/Foot **Center of the AER** did not develop properly