Limbs 2

Question 1

congenital limb malformations defects:

Grieg Syndrome:

Answer 1

syndactyly and polydactyly

Question 2

Apert syndrome:

Answer 2

syndactyly

Question 3

Holt-Oram syndrome:

Answer 3

phocomelia (short limbs)

Question 4

The three limb malformation syndromes are caused by autosomal recessive. true or false?

Answer 4

true

Question 5

ratio of limb malformations:

Answer 5

1:500 to 1:1000

Question 6

Phocomelia might be caused by environmental factorssuch as drugs. one example of this drug would be:

Answer 6

thalidomide

Question 7

Formation of limb buds:

Answer 7

24th and 28th day
- loose mesenchyme enclosed in epidermal jacket derived from lateral plate mesoderm
- The mesenchyme forms most of the
tissues in the limb, including bone, tendons, ligaments, dermis, muscle sheaths, and blood vessels.
- A ridge, known as the
apical ectodermal ridge (AER), forms at the distal end of the limb bud.

Question 8

what signal is transcribed in forelimb?

Answer 8

Tbx5

Question 9

what signal is transcribed in hindlimb?

Answer 9

Tbx4

Question 10

limb muscles are formed by epaxial myotome. true or false?

Answer 10

false. formed by hypaxial myotome

Question 11

Which muscle, dorsal or ventral, forms the supinators and extensor muscle of forelimbs, and flexor and abduction muscles of hindlimb?

Answer 11

dorsal muscles

Question 12

which digit differentiate first? then? last?

Answer 12

4;
3 and 2
1 and 5

Question 13

What is AER?

Answer 13

source of mitogen needed for limb outgrowth

Question 14

This protein
diffuses into limb bud mesenchyme and stimulates cell proliferation, thereby promoting limb
outgrowth:

Answer 14

FGF

Question 15

FGF is highly concentrated at which part of the limb?

Answer 15

phalanges

Question 16

At the proximal side, humerus, there is low FGF and high mitosis, stimulated by retinoic acid. True or false

Answer 16

true

Question 17

The posterior margin is an organizing centre for patterning the anterior-posterior axis of the limb
bud and is known as the

Answer 17

zone polarizing activity

Question 18

The ZPA at high concentrations specify digits at what region?

Answer 18

posterior

Question 19

SHH is expressed in the ZPA, and has concentration dependent manner. what is its role?

Answer 19

mimics function of ZPA when expressed in anterior mesenchyme

Question 20

in mice, Gli3 mutations enhance shh expression and cause:

Answer 20

polydactyly

Question 21

what is Acheiropodia?

Answer 21

absence of distal elements in the limbs. mutation caused by deletion of DNA that controls shh in the ZPA

Question 22

How does limb outgrowth cease?

Answer 22

• FGF activates shh
• shh in ZPA stimulates gremlin
• gremlin inhibits BMP (BMP inhibits FGF)
• limb outgrowth
• ZPA descendent cells cannot express gremlin
• go in between shh and gremlin domains
• stimulation of gremlin stops
• BMP is increased
• inhibition of FGF and outgrowth stops

Question 23

How do flaps of tissue between digits disappear?

Answer 23

Apoptosis occurs.
BMP signalling molecules present in interdigital regions
intensive cell death–> apoptosis

Question 24

incidence of syndactyly is most rare between which digits? and most common btw which digits?

Answer 24

1 and 2

3 and 4