Msi Week 1: Formation Of Limb Bud

Front 1

During which week does the upper limb appear?

Back 1

mid 4th week

Front 2

During which week does the lower limb appear?

Back 2

end 4th week

Front 3

From which part of the body wall does the limb bud project?

Back 3

Ventrolateral body wall

Front 4

From which region does the upper limb bud from?

Lower limb?

Back 4

Lower cervical region (C5-T1)

Lumbosacral region (L1-S3)

Front 5

Describe the organization of the limb bud. (Core composition and what covers it)

Back 5

Mesenchymal core covered by surface ectoderm

Front 6

What types of mesoderm form the mesenchymal core?

Back 6

1. Somatic mesoderm (forms connective tissue and skeleton)
2. Somitic mesoderm (myotome portion of somites invade core and form skeletal muscle)

Front 7

Which mesoderm forms the connective tissue and skeleton of the limb bud?

Back 7

Somatic mesoderm (from lateral plate mesoderm)

Front 8

Which mesoderm forms skeletal muscle?

Back 8

Somitic mesoderm (myotome portion)

(sclerotome portion forms axial skeleton)

Front 9

The limb bud is elongated in the _______ axis and narrow in the ________ axis.

Back 9

Elongated = craniocaudal axis
Narrow = dorsoventral axis

Front 10

Growth of the limb bud begins along which axis?

Back 10

Proximal-distal axis
(shoulder-->hand)

Front 11

List the 3 axes that limb buds grow in.

Back 11

1. Proximodistal
2. Craniocaudal
3. Dorsoventral

Front 12

What regulates the proximal-distal limb growth?

Back 12

Apical ectodermal ridge (AER)

Front 13

What is the apical ectodermal ridge (AER) composed of?

What induces its formation?

Back 13

Thickened ectoderm at apex of limb bud

Induced to form by underlying mesenchyme.

Front 14

What is necessary for the development and growth of the limb bud?

Back 14

Apical ectodermal ridge (AER)

Front 15

Proximal-distal growth is regulated by _____ and _____ signaling events in AER and underlying mesenchyme.

Back 15

Fgf and Wnt

Front 16

Absence of a limb is known as...?

Partial absence of a limb is known as...?

Back 16

Amelia

Meromelia

Front 17

If AER is injured during limb development there will be ______ (proximal/distal) deletions

Back 17

Distal

Front 18

Which genes are important in proximal-distal limb development that control temporal and spatial expression?

Back 18

Hox genes

Front 19

Which growth axis is influenced by the Zone of polarizing activity (ZPA)?

Back 19

Craniocaudal axis

Front 20

The zone of polarizing activity establishes gradients of which 2 morphogens?

Back 20

1. Sonic hedgehog (Shh)
2. Retinoic acid

Front 21

A high concentration of retinoic acid will encourage ______ (cranial/caudal) directionality.

Back 21

Caudal

Front 22

Which growth axis is regulated by signals from the mesenchyme and then from the ectoderm?

Back 22

Dorsal-ventral axis

Front 23

Which gene is expressed in the dorsal mesenchyme and regulates activity of Wnt7a which is expressed in the dorsal ectoderm?

Back 23

Lmx1b homeobox gene

(responsible for dorsal-ventral axis)

Front 24

What will be the result of a mutation of Lmx1b in humans?

Back 24

Nail-patella syndrome
(very small fingernails and absence of patella.
Lmx1b (along with Wnt7a) is involved in dorsoventral axis development)

Front 25

Between which weeks of development does the limb bud differentiate?

Back 25

4th - 8th

Front 26

During which time period are limbs the MOST sensitive to teratogens?

Back 26

4th - 5th weeks

Front 27

The limb is fully developed by which week?

Back 27

8th week

Front 28

Which structures are formed in the hand and foot plates when the mesenchyme condenses and patterned outlines of the digits are visible?

Back 28

Digital rays

(AER is maintained at tips)

Front 29

Which areas of the hand and foot plates lose AER (undergo programmed cell death)?

Back 29

Interdigital zone

Front 30

Which factors are expressed in the interdigital mesodermal cells that are involved in the signals leading to cell death?

Back 30

1. BMPs
2. Retinoic acid receptor B
3. Msx-1

Front 31

If cell death does not occur in the interdigital zone, what growth abnormality occurs?

Back 31

Syndactyly

Front 32

What growth abnormality results from addition digital rays?

Back 32

Polydactyly

Front 33

Explain the difference between the rotation of the upper limbs and lower limbs during development.

Back 33

Upper limb rotates laterally
Lower limb rotates medially

(Thumbs point laterally, big toes point medially)

Front 34

Describe the difference in placement of flexors/extensors in the upper limb verses those in the lower limb.

Back 34

Flexors/extensors have opposite placements in the upper and lower limbs.

Upper limb: flexors are ventral, extensors are dorsal

Lower limb: flexors are dorsal, extensors are ventral

Front 35

During endochondral ossification, where do primary centers of ossification form?

Back 35

Diaphysis

(blood vessels bring osteoblasts here)

Front 36

During endochondral ossification, where do secondary centers of ossification form?

When do they form?

Back 36

Epiphysis of long bones

Do not appear until AFTER birth

Front 37

After birth, which areas of long bones continues to grow?

Back 37

Epiphyseal plates
(located between epiphysis and diaphysis on both ends of bone)

Front 38

Describe the 4 steps of endochondral ossification.

Back 38

1. Aggregation of mesenchyme --mesoderm (early 5th week)
2. Cartilage model formed (5th - 7th week)
3. Blood vessels bring osteoblasts--primary centers of ossification begin in diaphysis (7th week)
4. Secondary centers of ossification form in epiphysis AFTER birth

Front 39

Synovial joint development forms from mesenchyme in which area?

Back 39

Interzonal area

Front 40

What does interzonal mesenchyme form?

Back 40

Articular cartilage on joint surfaces of neighboring bones

Front 41

Describe the structures formed from the center layer of interzonal mesenchyme.

Back 41

1. Internal structures of joint--menisci, enclosed joint ligaments
2. Synovial cavity

Front 42

Describe the structures formed from the outer layer of interzonal mesenchyme

Back 42

1. Joint capsule
2. Synovial membrane

Front 43

What types of muscles are formed in ventral muscle mass?

Back 43

Flexors
Adductors
Pronators

Front 44

What types of muscles are formed in dorsal muscle mass?

Back 44

Extensors
Abductors
Supinators

Front 45

The ______ primary rami from segmental spinal nerves provide motor innervation to the limbs.

Back 45

Ventral primary rami
(penetrate ventral and dorsal muscle masses)

Front 46

Name the 2 plexi that supply the upper extremity and the lower extremity.

Back 46

Upper extremity --> brachial plexus
Lower extremity --> lumbosacral plexus

(both formed by ventral primary rami of segmental spinal nerves)

Front 47

What is the term for the area of skin innervated by a single spinal nerve?

Back 47

Dermatome

Front 48

Describe the initial organization of dermatomes?
(which axes does the formation follow?)

Back 48

Cranial to caudal and proximal to distal

(later, rotation of the limbs cause dermatomes to spiral down limb)

Front 49

Term for anomaly in which distal structures are fully formed but proximal structures are absent.

Back 49

Phocomelia

Front 50

Syndactyly results from a mutation in which gene?

Back 50

HoxD13

Front 51

List 4 causes of limb abnormalities.

Back 51

1. Genetic factors (polydactyly, syndactyly..)
2. Environmental factors (teratogens--> meromelia, phocomelia..)
3. Mechanical (amniotic band syndrome)
4. Multifactorial (club foot)

Front 52

Name 2 teratogens that result in severe limb anomolies.

Back 52

1. Thalidomide
2. Retinoic acid (accutane)

Front 53

Which congenital anomolies typically result from thalidomide?

Back 53

1. Phocomelia
2. Meromelia

Front 54

Clubfoot is any deformity of the foot involving the ______.

Back 54

Talus

Front 55

What mechanical and genetic factors can result club foot?

Back 55

1. Abnormal intrauterine position
2. Genetic predisposition

Front 56

Which week of embryonic development is characterized by the appearance of the primitive streak, notochord, and 3 germ layers?

Back 56

3rd week

Front 57

During which developmental process are the three germ layers formed?

Back 57

Gastrulation
(bilaminar disc is converted into a trilaminar embryonic disc)

*occurs during 3rd week of development

Front 58

Which germ layer gives rise to the:
1. epidermis
2. Central/peripheral nervous system
3. Eye
4. Inner ear
6. Neural crest cells
7. Many connective tissues of the head

Back 58

Ectoderm

Front 59

Which germ layer is the source of
1. Epithelial linings of the respiratory and digestive tracts
2. Glands opening into the GI tract
3. Glandular cells of associated organs (liver, pancreas)

Back 59

Endoderm

Front 60

Which germ layer gives rise to all skeletal muscles?

Back 60

Mesoderm

Front 61

Which germ layer gives rise to blood cells and the lining of blood vessels, all visceral smooth muscular coats, the serosal linings of all body cavities, the ducts and organs of the reproductive and excretory systems, and most of the cardiovascular system?

Back 61

Mesoderm

Front 62

Which germ layer gives rise to all connective tissues, including cartilage, bones, tendons, ligaments, and skeletal muscle?

Back 62

Embryonic mesoderm

Front 63

What is the first sign of gastrulation?

Back 63

Appearance of the primitive streak

Front 64

How is the zone of polarizing activity activated?

Back 64

Fibroblast growth factors from the AER activate it.

Front 65

Blocking the signaling events of bone morphogenic proteins (BMPs) may result it what type of anomoly?

Back 65

Syndactyly
(webbing of the fingers or toes)

*BMPs play a role in apoptosis in the interdigital zones

Front 66

Digital rays begin to appear in the foot during which week of development?

Back 66

Week 7

Front 67

Separation of the digits occurs by which week?

Back 67

Week 8

Front 68

By which week of development are ossification centers present in all long bones?

Back 68

Week 12

Front 69

The primary axial artery becomes the _______ artery in the arm and the _______ artery in the forearm.

Back 69

Primary axial artery--->
Brachial A in ARM
Common interosseous A in FOREARM

Front 70

The primary axial artery becomes the _______ in the thigh and the ________and ________ arteries in the leg.

Back 70

Primary axial artery --->
Deep artery of the thigh (Profunda femoris A)
Anterior and posterior tibial arteris in leg

Front 71

During which week of development do finger and toenails begin to appear?

Back 71

Week 10

Front 72

Which axons arising from the spinal cord enter the limb bud first--motor or sensory?

Back 72

Motor enter first (week 5) and sensory axons follow, using the positioning of motor axons for guidance.

Front 73

What the is first blood vessel to supply the developing limb?

Back 73

Primary axial artery

Front 74

During development, what arteries arise from the aorta and supply the limb buds?

Back 74

Intersegmental arteries

Front 75

Suppression of limb bud development during the early part of the 4th week will result in what type of limb anomaly?

A disturbance during the 5th week will result in...?

Back 75

4th week --> amelia
5th week --> meromelia

Front 76

Anomaly that results from a reduction in the length of the phalanges, causing shortness of the digits.

Back 76

Brachydactyly

Front 77

What is the most common anomaly of the hand or foot?

Back 77

Syndactyly