Development of Limbs

Question 1

Describe what is created from the lateral plate mesoderm

Answer 1

Splanchic = circulatory system
Somatic = body cavity, pelvis, limb bones and tendons
Extraembryonic

Question 2

Describe what is created from the intermediate mesoderm

Answer 2

Kidney and gonads

Question 3

Describe what is created from the paraxial mesoderm

Answer 3

Head and somites

Somites = sclerotome, myotome, dermatome

Question 4

When do upper limb buds form?

Answer 4

Day 24

Question 5

When do lower limb buds form?

Answer 5

Day 25-26

Question 6

What do limb buds form deep to?

Answer 6

The apical ectodermal ridge (AER) which is a thick band of ectoderm that the limb buds form deep to

Question 7

What grows out from that AER?

Answer 7

Proliferation of mesenchyme from the lateral plate mesoderm

Question 8

What is the stylopod region?

Answer 8

Humerus or femur

Question 9

What is the zeugopod region?

Answer 9

Radius/ulna or tibia/fibula

Question 10

What is the autopod region?

Answer 10

Carpals, metacarpals, phalanges or tarsals, metatarsals, phalanges

Question 11

What are the axes of the limb bud?

Answer 11

Proximal - Dorsal
Cranial - Caudal
Dorsal - Ventral

Question 12

Describe the initiation of limb bud growth

Answer 12

FGF10 induces the formation of AER and AER secretes FGF8 which positively regulates FGF10 to stimulate more AER

Question 13

What is the importance of FGF signaling?

Answer 13

It is essential for the INITIATION of limb bud development and for the proximal - distal axis to form

Question 14

What happens if AER is completely removed?

Answer 14

NO limb formation

Question 15

What happens if AER is removed later in development?

Answer 15

Loss of distal elements

Question 16

Meromelia

Answer 16

Absence of part of a limb caused by intermediate or late loss of FGF signaling

Question 17

Amelia

Answer 17

Absence of an entire limb caused by early loss of FGF signaling

Question 18

Phocomelia

Answer 18

Loss of long bones with hands/feet attached proximally

Question 19

What can cause phocomelia?

Answer 19

Partial loss of FGF signaling or HOX disruption due to thalomide

Question 20

Adactyly

Answer 20

Absence of digits caused by late loss of FGF signaling

Question 21

Ectrodactyly

Answer 21

Split hand/foot - “lobster claw”

Question 22

What causes ectrodactyly

Answer 22

Partial absence of FGF8 from AER or EEC syndrome

Question 23

What creates the cranial - caudal axis?

Answer 23

Zone of polarizing activity (ZPA)

Question 24

What supports ZPA function?

Answer 24

SHH!

Question 25

What happens when there is an overexpression of SHH?

Answer 25

A second ZPA is created and duplicated digits emerge

Question 26

Polydactyly

Answer 26

Dominant trait; presence of supernumary digits where extra digits lack normal growth and musculature

Question 27

What do HOX genes regulate?

Answer 27

Cranial - caudal and proximal - distal axes

Question 28

What is a paralog?

Answer 28

Genes related due to descent from a common ancestral DNA sequence

Question 29

What hox gene specifies stylopod?

Answer 29

HOX9/10

Question 30

What hox gene specifies zeugopod?

Answer 30

HOX11

Question 31

What hox gene specifies autopod?

Answer 31

HOX12/13

Question 32

Brachydactyly

Answer 32

Shortened finger/toe bones due to genetic changes in HOX13 or PTHLH

Question 33

What creates the dorsal surface?

Answer 33

Wnt7a

Question 34

What creates the ventral surface?

Answer 34

EN1 (engrailed)

Question 35

What gives negative feedback to the Wnt7a?

Answer 35

EN1

Question 36

How are individual digits formed?

Answer 36

Interdigital mesenchyme apoptosis

Question 37

What stimulates interdigital mesenchyme apoptosis?

Answer 37

Increased BMP = Increased cell death

Question 38

When do separate digits fully form?

Answer 38

8th week

Question 39

What is syndactyly?

Answer 39

Fusion of digits due to no digital rays

Question 40

What are the 2 types of syndactyly?

Answer 40

Cutaneous and osseous

Question 41

Cutaneous syndactyly

Answer 41

Webbing between digits fails to degenerate; BMP signaling disruption that causes no apoptosis

Question 42

Osseous syndactyly

Answer 42

Fusion of bones; HOXD13 mutation

Question 43

Describe how limbs get their muscle mass

Answer 43

Dermamyotome from the paraxial mesoderm migrates to the limb bud and differentiates into myoblasts to form the ventral and dorsal muscle masses

Question 44

What does the dorsal muscle mass become?

Answer 44

Extensors, ABductors and supinators

Question 45

What does the ventral muscle mass become?

Answer 45

Flexors, ADDuctors and pronators

Question 46

What innervates the dorsal muscle mass?

Answer 46

Dorsal branches of VENTRAL rami

Question 47

What innervates the ventral muscle mass?

Answer 47

Ventral branches of ventral rami

Question 48

List the pathway for arterial supply to the upper limb

Answer 48

Dorsal intersegmental A. Primary axial A. Brachial A. and common interosseous A. Ulnar A. and Radial A.

Question 49

List the pathway for arterial supply to the lower limb

Answer 49

Dorsal intersegmental A. Primary axial A. Deep A. of the thigh, Anterior tibial A., Posterior tibial A.

Question 50

Describe the venous supply

Answer 50

Primary axial A, marginal sinus, peripheral vein

Question 51

Which way does the upper extremity rotate?

Answer 51

Laterally

Question 52

Which way does the lower extremity rotate?

Answer 52

Medially

Question 53

Amniotic bands

Answer 53

Adhesions between amnion and fetal structures; prevents growth or pinches off structure

Question 54

Bilateral talipes equinovarus

Answer 54

Club foot; caused by oligohydramnios - low amniotic fluid volume reduces fetal movements