Development of the Skeletal System

Question 1

Vertebrae form from adjacent sclerotomes

Answer 1

True

Sclerotomes split into cranial and caudal sections to let spinal nerves grow out and touch myotomes

Question 2

Herniated disc

Answer 2

Nucleous pulposis leaking out to where dorsal roots are (spinal canal) (usually posteriorly)

Question 3

Scoliosis results from what?

Answer 3

Abnormal formation and segmentation of the vertebral precursors (somites)

Question 4

Ribs arise from what?

Answer 4

Condensed mesenchyme lateral to the body of the vertebra

Question 5

Cervical ribs are usually removed but lumbar ribs are left in

Answer 5

True

Question 6

What is pectus excavatum?

Answer 6

Sternum sunken posteriorly (down into chest)

Failure to fuse at midline. Sternum develops from cartilaginous sternal bars in ventral body wall

Assumed to be caused by overgrowth of costal cartilage

Question 7

What is pectus carinatum?

Answer 7

Overgrowth of cartilage causing sternum to protrude. Can be evident at birth and during growth spurt, more common in males

Question 8

Sternal Foramen

Answer 8

Hole in sternum

Directly over the heart and common acupuncture point and need to be careful so heart is not punctured

Question 9

Hox gene

Answer 9

Lays out limbs on axis, where they are put

Signaling between ectoderm and mesoderm

Question 10

Holt-Oram Syndrome

Answer 10

Mutation in TBX5 (forelimb) –> upper limb abnormalities (i.e. fusions of carpal bones, hands very close to body/short arm)

Question 11

Amelia vs mereomelia

Answer 11

Amelia: whole limb missing
Meromelia: part missing

Question 12

Mesomelia

Answer 12

Shortened forearm or leg elements (one arm shorter than the other, radius/ulna shorter than humerus)

Question 13

Thalidomide

Answer 13

Further from the AER thinks it’s proximal

It messes up signal from AER to progress zone

When FGF stops, you get a hand or foot

Question 14

Syndactyly

Answer 14

Webbed fingers

Failure of programed apoptosis

Question 15

Brachydactyly/short digits

Answer 15

Dominant trait, short digits (people usually have short stature)

Question 16

Cleft hand/foot

Answer 16

Lobster-claw, absence of central digits

Question 17

Muscle cells come from what?

Answer 17

Hypaxial mesoderm

Question 18

Schawnn cells come from what?

Answer 18

Neural crest

Question 19

Motor/sensory axons come from what?

Answer 19

Neural tube

Question 20

Achondroplasia

Answer 20

Dwarfism-affects long bones

FGF-R3 mutation

Autosomal dominant

Question 21

Osteogenesis Imperfecta/Brittle Bone Disease

Answer 21

Bone fragility

Blue sclera

Question 22

Talipes equinovarus (Club foot)

Answer 22

Sole of foot is turned medially and foot is inverted

Question 23

Signal pathway

Answer 23

HOX → TBX 5 (forelimb, anterior), TBX4 (hindlimb) starts growth → Radical fringe (dorsal ectoderm) or Engrailed-1 (ventral)- these restrict location of AER → AER (sends signal to grow) →FGF →gets PZ (progress zone) cells to divide and grow (at tip of limb), ZPA (zone of polarizing activity- lays out radius, ulna, tarsals but needs building materials) → ZPA triggers SHH, retinoic acid (too much=extra limb), finger/limb organization (cells closer to AER=digits)