Embryology

Question 1

When do limb buds appear?

Answer 1

At 4 weeks

Question 2

3 planes of limb bud development

Answer 2

Proximal-distal, dorsal-ventral, anterior-posterior

Question 3

What gene regulates proximal-distal limb development

Answer 3

FGF

Question 4

Describe production of FGF

Answer 4

Initially produced by mesoderm which causes the AER to form, then produced by AER to signal proliferation in mesoderm

Question 5

Describe how digits form

Answer 5

Apoptosis of cells in the AER to separate it into five digits

Question 6

Wnt-7a

Answer 6

Signalling protein expressed by AER that activates LMX-1 in the mesoderm to form dorsal structures

Question 7

LMX-1

Answer 7

Activated by Wnt-7a, responsible for forming dorsal structures

Question 8

Deletion of LMX-1 causes

Answer 8

both sides to be ventral

Question 9

Engrailed1

Answer 9

Activated by the ectoderm on the ventral side of the limb to repress WNT-7a, to create a ventral and dorsal side

Question 10

Shh

Answer 10

Signalling protein produced at posterior base of limb buds

Question 11

Zone of Polarizing Activity

Answer 11

Area that produces Shh

Question 12

Placing Shh or ZPA to anterior limb bud would cause

Answer 12

mirror duplication of structures

Question 13

Hox genes

Answer 13

Activated by Shh diffusing across limb bud, responsible for differentiation pattern of anterior-posterior digits and segmental organization of entire embryo cranial-caudal

Question 14

Gene responsible for proximal-dorsal limb development

Answer 14

FGF

Question 15

Genes responsible for dorsal-ventral limb development

Answer 15

Wnt-7a, LMX-1, engrailed1

Question 16

Genes responsible for anterior-posterior limb development

Answer 16

Shh, Hox

Question 17

Genes responsible for cranial-caudal segmental organization of embryo

Answer 17

Hox

Question 18

Ossification type used for long bones

Answer 18

Endochondral ossification

Question 19

Ossification type used for flat bones of skull and face

Answer 19

Intramembranous ossification

Question 20

Mesenchyme

Answer 20

Loosely organized, mesodermal tissue that develops into connective and skeletal tissues

Question 21

Process of intramembranous ossification

Answer 21

Mesenchyme cells differentiate directly into osteoblasts

Question 22

Process of intramembranous ossification

Answer 22

Mesenchyme differentiates into chondroblasts which produce a cartilage model that then becomes vascularized, introducing osteoblasts. Chondrocytes get stuck at the epiphyses.

Question 23

Layers of epiphyseal plate

Answer 23

Resting, proliferation, hypertrophy, calcification, ossification

Question 24

Zone of calcification

Answer 24

where chondroblasts mineralize the surrounding matrix

Question 25

Zone of hypertrophy

Answer 25

where chondroblasts undergo apoptosis

Question 26

Zone of ossification

Answer 26

where osteoblasts bind to mineralized matrix and deposit bone matrix

Question 27

What area of trilaminar embryo becomes skeletal muscle?

Answer 27

Paraxial mesoderm (closest to notochord and neural tube)

Question 28

Somites

Answer 28

Segments in a cranial-caudal sequence in the trunk

Question 29

Somites differentiate into

Answer 29

Axial skeleton, some dermis, all skeletal muscle

Question 30

When do axons of motor neurons enter the limb bud

Answer 30

During 5th week

Question 31

When do axons of sensory neurons enter the limb bud

Answer 31

Soon after the motor neuron axons enter

Question 32

Dermatome

Answer 32

Area of the skin innervated by one spinal nerve

Question 33

When do limbs rotate?

Answer 33

6-8 weeks

Question 34

In what way do limbs rotate?

Answer 34

Arms laterally and legs medially

Question 35

When are embryos susceptible to limb malformations?

Answer 35

4-5 weeks

Question 36

Reduction deficit

Answer 36

All or part of limb is missing

Question 37

Types of reduction deficit

Answer 37

Meromelia, amelia, phocomelia

Question 38

Thalidomide effects

Answer 38

Amelia at week 4, meromelia at week 5

Question 39

Mechanism of thalidomide

Answer 39

Disrupts AER and its production of FGF

Question 40

Duplication defect

Answer 40

Extra limb elements are present

Question 41

Example of duplication defect

Answer 41

Polydactyly

Question 42

Polydactyly

Answer 42

Shh is expressed in anterior limb bud, causing mirror extra digits. Caused by ZPA duplication

Question 43

Dysplasia

Answer 43

Malformation of part of limb

Question 44

Example of dysplasia

Answer 44

Syndactyly

Question 45

Syndactyly

Answer 45

Abnormal fusing of the digits from reduced apoptosis in AER