Limb Development

Question 1

Sclerotome will give rise to ___ bones

Answer 1

axial

Question 2

Dermomyotome will give rise to ___ ______ muscles

Answer 2

all skeletal

Question 3

somatic mesoderm will give rise to _____ bones

Answer 3

appendicular

Question 4

Intramembranous ossification

Answer 4

no cartilaginous cells are involved, forms flat bones (aka dermal or membrane bones) - facial bones, cranial vault, part of clavicle

Question 5

endochondral ossification

Answer 5

cartilaginous cells are replaced by osseous cells, forms most bones of the body - cranial base, pharyngeal cartilages, vertebrae, thoracic cage, appendicular bones, part of clavicle

Question 6

Synovial joint formation

Answer 6

Interzonal mesenchyme differentiates into fibroblastic tissues, which give rise to peripheral and central structures. Peripherally - articular cartilages & joint capsule. Centrally - synovial cavity, enclosed joint ligaments, menisci

Question 7

Cells of skeletal myogenesis - cell origins

Answer 7

segmented paraxial mesoderm, unsegmented paraxial mesoderm, prechordal plate mesoderm

Question 8

Cells of skeletal myogenesis - cell types

Answer 8

myoblasts (myofibers) & satellite cells (myofibers)

Question 9

Cells of skeletal myogenesis - development waves

Answer 9

embryonic (myoblasts), fetal (myoblasts), and postnatal/adult (satellite cells)

Question 10

Dermamyotomes differentiate into

Answer 10

dermatomes and myotomes

Question 11

Myotomes further differentiate into

Answer 11

epimere and hypomere populations

Question 12

Dermamyotome derivatives

Answer 12

dermatome, epimeres, and hypomeres

Question 13

dermatome give rise to

Answer 13

primarily dermis of the back and neck

Question 14

epimeres give rise to

Answer 14

intrinsic back muscles (epaxial muscles)

Question 15

Hypomeres give rise to

Answer 15

all other skeletal muscles (hypaxial muscles)

Question 16

The hypomere associates with and divides into 2 distinct populations on either side of the somatic lateral plate mesoderm -

Answer 16

ventral muscle mass and dorsal muscle mass

Question 17

Ventral muscle mass (AKA preaxial muscle mass)

Answer 17

Will form the flexors, adductors, and pronators in the upper limb and in the lower limb

Question 18

Muscles formed from ventral muscle mass in upper limbs

Answer 18

pectoralis major and minor, subclavius, anterior arm muscles, anterior/volar forearm muscles, palmar/volar hand muscles

Question 19

Muscles formed from ventral muscle mass in lower limbs

Answer 19

medial thigh muscles, posterior thigh muscles, posterior leg muscles, plantar foot muscles, gemellus superior and inferior, obturator internus, and quadratus femoris

Question 20

Dorsal muscle mass (AKA postaxial muscle mass)

Answer 20

will form extensors, abductors, and supinators in the upper limbs and lower limbs

Question 21

Muscles formed from dorsal muscle mass in upper limbs

Answer 21

scapular muscles, latissimus dorsi, posterior arm muscles, posterior forearm muscles, lateral hand muscles

Question 22

Muscles formed from dorsal muscle mass in lower limbs

Answer 22

gluteal muscles, anterior thigh muscles, biceps femoris, anterior leg muscles, lateral leg muscles, dorsal foot muscles

Question 23

When and where do limb buds begin developing?

Answer 23

They begin forming on the ventrolateral body wall during week 4 of development

Question 24

When are both limb buds fully developed?

Answer 24

By the end of week 8

Question 25

Limb buds differentiate and grow in 3 axis -

Answer 25

proximal-distal axis, cranial-caudal axis, dorsal-ventral axis

Question 26

Proximal-distal axis

Answer 26

defined along the length of the limb, such as from the shoulder to fingers or hip to toes

Question 27

Cranial-caudal axis

Answer 27

defined along the breadth of the limb, such as from thumb to pinky or big to little toes

Question 28

Dorsal-ventral axis

Answer 28

defined along the depth of the limb, such as from the knuckles to the palm or knee to popliteal region

Question 29

What is the Apical ectodermal ridge (AER)

Answer 29

required for proximodistal growth, it is a thickened portion of ectoderm at the apex of the limb bud

Question 30

What induces the formation of the AER?

Answer 30

Underlying mesenchyme

Question 31

What hormone does the AER produce in order to stimulate the mesenchymal core of the limb bud to proliferate, pushing the AER away from body wall?

Answer 31

fetal growth factor (Fgf)

Question 32

stylopod

Answer 32

the most proximal region and first to develop from AER, forms the arm and thigh bones

Question 33

zeugopod

Answer 33

the intermediate region and second to develop from AER, forms the forearm and leg bones

Question 34

autopod

Answer 34

the distal region and last to develop from AER, forms the hand and foot bones

Question 35

Disruption in AER will result in

Answer 35

distal deletions

Question 36

amelia

Answer 36

an anomaly where no structures of the limb formed due to early complete loss or disruption of AER

Question 37

meromelia

Answer 37

an anomaly where the distal structures present are malformed with the most distal structures of the limb completely absent due to late complete loss or disruption of AER

Question 38

cleft hands or feet (AER)

Answer 38

anomalies where the middle digits of a limb are absent due to late partial loss or disruption of AER

Question 39

Homebox (HOX) genes

Answer 39

critical in determining proximodistal patterning - they direct morphological changes during development.

Question 40

Absence of 1 or more HOX genes during development can lead to

Answer 40

middle deletions such as phocomelia - an anomaly where distal limb structures formed on proximal structures and intermediate structures are missing

Question 41

Zone of polarizing activity (ZPA)

Answer 41

drives craniocaudal differentiation - it is a defined region along the caudal/postaxial border of the limb bud that produces sonic hedgehog (Shh)

Question 42

When does Shh expression happen and what does it do?

Answer 42

After the hand or foot plate forms, Shh expression will happen to stimulate the formation of digits

Question 43

Disruption of the ZPA can result in

Answer 43

aberrant digit enumeration

Question 44

Polydactyly

Answer 44

an anomaly where there are more than 5 digits present on a limb, which can be caused by excessive Shh expression or a larger than normal ZPA

Question 45

Oligodactyly or adactyly

Answer 45

anomalies where there are less than 5 digits present on a limb or a complete absence of digits, respectively, which can result from insufficient Shh expression or an absent ZPA

Question 46

Cleft hands or feet (ZPA)

Answer 46

anomalies where the middle digits of a limb are absent, which can result from complex disruptions of the ZPA

Question 47

what is the role of lmx1b, wnt7a, and en1?

Answer 47

dorsoventral patterning

Question 48

Lmx1b

Answer 48

a specific hox gene involved in limb morphogenesis in the dorsal-ventral axis, expressed in the dorsal mesenchymal core of the limb bud, mediates the activity of Wnt7a

Question 49

Wnt7a

Answer 49

A member of the Wnt family of genes, expressed by the dorsal ectoderm covering the limb bud, stimulates dorsalization via Lmx1b

Question 50

En1

Answer 50

expressed by the ventral ectoderm covering the limb bud, inhibits activity of Wnt7a, thereby promoting ventralization

Question 51

Nail-patella syndrome

Answer 51

an anomaly characterized by soft or absent nail beds in the limbs and a lack of a patella due to mutation in Lmx1b

Question 52

Upper limb rotates _____ to position structures

Answer 52

laterally

Question 53

Lower limb rotates ______ to position structures

Answer 53

medially

Question 54

amniotic band syndrome

Answer 54

an anomaly similar to meromelia where the most distal structures of the limb are absent, however proximal portions of limbs are normal - occurs due to amniotic bands (scar tissue that can form in the womb) that wraps around the limb or digits during development and causing ischemic amputation

Question 55

Club foot

Answer 55

an anomaly that is characterized by a sharp medial curvature of the foot and ankle. Caused by reduced space in the womb due to oligohydramnios or a naturally small womb with a large fetus.

Question 56

Thalidomide and limb development