Embryology

Question 1

How do limbs develop ?

Answer 1

Begins with limb buds

Question 2

When do the limb buds for the upper limb appear?

Answer 2

Day 26

Question 3

When do limb buds for lower limbs appear?

Answer 3

Day 28

Question 4

What stimulates the somatic layer of lateral plate mesoderm to evaginate?

Answer 4

Somites

Question 5

What forms a core of mesenchyme covered by surface ectoderm?

Answer 5

Somatic layer of lateral plate mesoderm

Question 6

The mesenchyme directs the organization of myotomes to form structures

Answer 6

Bones
Tendons 
Ligaments
Cartilage
Fascia 
Joints vessels
Dermis

Question 7

What structures contribute to the formation of limbs?

Answer 7

Epidermis
Muscles
Nerves
Melanocytes

Question 8

What embryonic structures are associated with epidermis, muscles, nerves, and melanocytes?

Answer 8

Aer
Somites
Neuroectoderm
Neural crest 
Respectively

Question 9

The limb buds grow mainly by what process?

Answer 9

Proliferation of mesenchyme

Question 10

What genes regulate axes and patterning?

Answer 10

Hox genes

Question 11

What forms at the apex of limb bud?

Answer 11

It thickens and forms apical ectodermal ridge

Question 12

What does the Aer signal for?

Answer 12

Proliferation of the underlying mesenchyme

Question 13

What is formed when mesenchymal cells aggregate at the posterior margin of the limb bud?

Answer 13

Zone of polarizing activity (ZPA)

Question 14

What is the zone of polarizing activity responsible for?

Answer 14

Patterning of anterior/posterior axis

Question 15

Retinoic acid

Answer 15

Shown to disrupt the development of limbs

Question 16

When do the mesenchyme in the hand and foot plates condense to form digital rays?

Answer 16

6th and 7th week respectively

Question 17

What induces the mesenchyme to form bones at the tips of digital rays?

Answer 17

Aer

Question 18

When does chondrification centers appear ?

Answer 18

5th week

Question 19

When do cartilaginous models of all limb bones appear?

Answer 19

6th week

Question 20

When does osteogenesis begin?

Answer 20

8th week

Question 21

When do the ossification of limb bones occur?

Answer 21

Begins toward the end of the embryonic period (week 8)

Question 22

What is the composition of epiphyses at the time of birth?

Answer 22

Shafts of the long bones are ossified but epiphyses are still cartilage

Question 23

How do the embryonic limbs obtain anatomical position?

Answer 23

Rotation of limbs
The upper limbs rotate laterally through 90 degrees on their long axis- extensors on the dorsal aspect of upper limb
The lower limb rotates medically almost 90 degrees - extensors on anterior aspect of lower limb

Question 24

How do the limbs get innervated?

Answer 24

Motor axons from spinal cord each the dorsal and ventral muscle masses during 5th week
Motor neurons grow first

Question 25

Dermatomes

Answer 25

Refer to segmental bands of skin innervated by spinal cord segment As limbs elongate, the cutaneous distribution migrates along the limbs There is a significant OVERLAP b/n dermatomes

Question 26

What is the blood supply to the limbs?

Answer 26

Dorsal intersegmental arteries that arise from dorsal aorta | Primordial vascular pattern consists of primary axial arteries and its branches

Question 27

What do the axial artery of the upper limb become!?

Answer 27

Brachial and continues as the common interosseous | The radial and ulnar arteries as secondary branches of the brachial

Question 28

What artery typical degenerates?

Answer 28

Median artery

Question 29

What becomes of the Axial artery of the lower limb?

Answer 29

Profunda femoris Popliteal Posterior tibial

Question 30

Which weeks are the most critical for limb development?

Answer 30

4th and 5th weeks

Question 31

What did thalidomide cause?

Answer 31

Many limb defects The drug was used to tx morning sickness

Question 32

What usually causes limb defects?

Answer 32

Genetic factors

Question 33

Achondroplasia

Answer 33

Cause of dwarfism Limbs are bowed and short Disturbance of endochondral ossification at epiphyseal plates

Question 34

Thanatophoric dysplasia

Answer 34

Lethal skeletal dysplasia Infants die soon after birth because of respiratory failure (muscles?ribs?) Attributed to fibroblast growth factor receptor deficiency

Question 35

What is Amelia?

Answer 35

Absence of an entire limb

Question 36

Meromelia

Answer 36

Absence of a part of a limb

Question 37

What is cleft hand or foot?

Answer 37

Lobster claw deformity - fusion of digital rays Absence of central digits - fusion of digital rays Failure of digital rays to form-absence of digits

Question 38

Floating thumb

Answer 38

Absence of the metacarpal bone in the thumb

Question 39

Congenital absence of the radius

Answer 39

Radius failed to for, | Hand deviates laterally

Question 40

Brachydactyly

Answer 40

The digits are relatively short | Associated with short stature

Question 41

Polydactyly

Answer 41

Supernumery digits Extra division of digital rays Extra digit Usually useless

Question 42

Syndactyly

Answer 42

Defect is characterized by the fusion of the digital rays | Can be cutaneous (webbing of the digits) or Osseous (fusion of the bones)

Question 43

Congenital club foot

Answer 43

Talipes Any defect involving the talus results from abnormal orientation of the foot that prevents normal weight bearing May be caused by environmental factor

Question 44

Congenital dislocation of the hip

Answer 44

Defect results from laxity of the joint capsule or underdevelopment of the acetabulum

Question 45

Genuine recurvatum

Answer 45

Congenital hyper extension of the knee | Returns to normal alignment without intervention