Embryo - Development of Skeletal System

Question 1

Vertebrae form as _______ structures derived from adjacent _______.

Answer 1

intersegmental; sclerotomes

Question 2

There are originally ___ cervical somites, but fusion results in __ cervical nerves

Answer 2

8 cervical somites; 7 cervical nerves

Question 3

Cervical spinal nerves exit ______ (above/below) vertebra of same number, while other spinal nerves exit ______ (above/below).

Answer 3

Cervical nerves exit above

Other nerves exit below

Question 4

_______ form neural arches surrounding the developing spinal cord

Answer 4

Sclerotomes

Question 5

Congenital Scoliosis

Answer 5

Abnormal lateral curvature of the spine, resulting from disruption of normal vertebral development

Question 6

Types of Congenital Scoliosis

Answer 6

A - failure of formation of vertebrae
B - failure of segmentation of vertebrae
C - mixed

Question 7

Where do ribs arise from?

Answer 7

Zones of condensed mesenchyme lateral to the body of the vertebra
Develop from costal processes

Question 8

The sternum develops from:

Answer 8

Cartilaginous sternal bars in ventral body wall

Question 9

In what direction do the sternal bars fuse?

Answer 9

Cranial-caudal direction

Question 10

Defects of the Sternum

Answer 10

Sternal Cleft
Pectus excavatum
Pectus Carinatum

Question 11

Pectus Excavatum

Answer 11

Assumed to be caused by overgrowth of the costal cartilage. Costal cartilage overgrowth restricts the expansion of the ribs and pushes the sternum inward.

Question 12

Pectus Carinatum

Answer 12

Overgrowth of cartilage causing sternum to protrude. May occur as solitary congenital abnormality or in association with other genetic disorders or syndromes. Can be evident at birth or in adolescent males during growth spurt (most common)

Question 13

Sternal Foramen

Answer 13

Ossification anomaly found in 4-10% of population.
Can be mistaken for bullet wound or sternal disease by CT scan.
Common acupuncture point
Directly over heat

Question 14

When does outgrowth of the body wall begin?

Answer 14

Late in week 4 of development, FL>HL

Question 15

Positioning of the limbs along the craniocaudal axis is regulated by the ____ genes expressed along the axis

Answer 15

HOX genes

Question 16

Once positioning along the craniocaudal axis is determined, limb growth must be regulated along the:

Answer 16

proximodistal, anteroposterior, dorsoventral axes

Question 17

Limb outgrowth in the forelimb is initiated by:

Answer 17

TBX5 and FGF10

Question 18

Limb outgrowth in the hindlimb is initiated by:

Answer 18

TBX4 and FGF10

Question 19

Meromelia

Answer 19

Part of limb is missing

Question 20

Amelia

Answer 20

All of limb is missing

Question 21

Phocomelia

Answer 21

Feet and hands arise close to the trunk

Question 22

Mesomelia

Answer 22

Shortened forearm or leg elements

Question 23

Radial Club Hand

Answer 23

Congenital absence or hypoplasia of the radial structures of the forearm and hand
Hypoplastic or absent muscular structures and radial nerve
Treatment is best if early passive stretching exercises and corrective casting is started

Question 24

Once limb outgrowth is initiated, BMPs, expressed in ventral ectoderm, induce formation of the _____ _______ ______

Answer 24

Apical Ectodermal Ridge (AER)

Question 25

Apical Ectodermal Ridge (AER)

Answer 25

Thickened ectoderm on apex of limb bud Directs limb bud organization along proximo-distal axis Maintains dorsal/ventral axes

Question 26

After AER is established, it expresses _____ and _____, which maintain the progress zone.

Answer 26

FGF4 and FGF8

Question 27

Zone of Polarizing Activity (ZPA)

Answer 27

Mesodermal cells located at base of limb

Question 28

What does the ZPA produce?

Answer 28

Produces Retionic Acid which initiates expression of SHH

Question 29

The ZPA directs:

Answer 29

``` Organization of limb bud and pattering of digits Determines anterior (preaxial/thumb), posterior (postaxial) ```

Question 30

Misexpression of retinoic acid and SHH results in:

Answer 30

A mirror image duplication of the limb structures

Question 31

Polydactyly

Answer 31

Extra digits Commonly medial or lateral, rather than central Dominant trait

Question 32

In what direction do limbs grow and develop?

Answer 32

Proximo-distally

Question 33

Progress Zone (PZ)

Answer 33

Where mitosis and limb lengthening occurs

Question 34

Zone of Cell Division (Progress Zone)

Answer 34

Region of actively dividing cells

Question 35

Zone of Differentiation

Answer 35

Region of cell specialization

Question 36

_____ genes regulate type/shape of bones

Answer 36

HOX

Question 37

AER secretes FGFs that influence the closest cells (progress zone) to develop into _____ structures. Cells no longer within range of AER remain _____ in nature.

Answer 37

Distal | Proximal

Question 38

Thalidomide

Answer 38

Disrupts signal from AER down to the progress zone Cells in progress zone may divide a little or not at all (Hansons disease)

Question 39

Syndactyly

Answer 39

Most common limb abnormality Webbed fingers or toes Failure of programmed apoptosis in digital ray Simple dominant or simple recessive inheritance

Question 40

Where is syndactyly most frequent?

Answer 40

Between 3rd & 4th fingers and 2nd & 3rd toes

Question 41

Brachydactyly

Answer 41

Uncommon Reduction in the length of phalanges Inherited as dominant trait Short stature

Question 42

Cleft hand or foot

Answer 42

Uncommon Lobster-claw Absence of one or more central digits or between digits 2 & 4 Cleft hand/foot is divided into 2 parts that oppose each other Remaining digits are partly or completely fused

Question 43

Contribution of Lateral Plate Mesoderm to developing limb bud:

Answer 43

Skeleton and Vasculature

Question 44

Contribution of Hypaxial Mesoderm to developing limb bud:

Answer 44

Muscles

Question 45

Contribution of Neural Crest to developing limb bud:

Answer 45

Schwann cells

Question 46

Contribution of Neural Tube to developing limb bud:

Answer 46

Motor/Sensory axons (dermatome map)

Question 47

How do upper limbs rotate?

Answer 47

90 degrees laterally

Question 48

How do lower limbs rotate?

Answer 48

90 degrees medially

Question 49

Malformations

Answer 49

Overgrowth Undergrowth Focal Defects Associated w/ other general/syndromic skeletal abnormalities

Question 50

Sirenomelia

Answer 50

"Mermaid Syndrome" Different Classifications Separation surgery possible in some cases

Question 51

Achondroplasia

Answer 51

Most prevalent form of dwarfism Mutation on FGF-R3 Pathogenic changes at epiphyseal plate; zones of proliferation & hypertrophy are narrow and disorganized Autosomal dominant

Question 52

Osteogenesis Imperfecta/Brittle Bone Disease

Answer 52

Bone fragility that predisposes to fractures and deformities related to connective tissue abnormalities (Collagen deformation) Blue Sclera Not always evident at birth

Question 53

Talipes equinovarus (Club Foot)

Answer 53

Most common type of club foot The sole of the foot is tuned medially and the foot is inverted. 1/1000 births, two times more frequent in males

Question 54

Flexible Club Foot

Answer 54

Results from abnormal positioning or restricted movement of the lower limbs in utero. Structurally normal feet Usually correct themselves spontaneously

Question 55

Rigid Club Foot

Answer 55

Abnormal development of the ankle and foot joints during the 6th and 7th week Bony deformities, particularly the talus