Limbs

Question 1

Limb function

Answer 1

Movement

Fat & calcium storage

Blood production sites (Pelvis & leg bones)

Question 2

Limb functional modules (common btwn legs & arms)

Answer 2

Stylopod (humerus/femur)

Zeugopod (radius/ulna, tibia/fibula)

Autopod (Carpals/Tarsals, metacarpals/metatarsals, phalanges)

Question 3

Limb Buds

Answer 3

Hox patterning dictates limb bud position:

• Forelimb btwn Hox5 and Hox6
• Hindlimb btwn Hox9 and Hox10

Limb buds initiated by Fibroblast Growth Factor (FGF)

Question 4

Limb identity determinant?

Answer 4

T-box genes (distinguish btwn arms & legs)

Question 5

Proximal-distal patterning determinant?

Answer 5

Apical ectodermal ridge (AER)

Question 6

Medial-lateral patterning determinant?

Answer 6

Sonic Hedgehog

Mutations in Shh can result in additional digits

Question 7

Digit formation

Answer 7

Apoptosis separates digits

Question 8

Webbed digits?

Answer 8

Syndactyly (lack of apoptosis) - most common limb defect

Question 9

Limb evolution?

Answer 9

Fingers evolved from lobe-fins on fish

Shoulder girdle separates from dorsal midline

Forelimb emphasizes versatility / mobility, hindlimb emphasizes stability and power

Question 10

Sprawling -> Erect posture

Answer 10

Reduced resistance lever arm; better locomotion