Development of the Upper and Lower Limb

Question 1

When do Upper limb buds + lower limb buds appear

Answer 1

Upper limb buds-day 26 or 27,

lower limb buds- 1 or 2 days later.

Question 2

Upper limb buds develop opposite -

Answer 2

he caudal cervical segment,

Question 3

lower limb bud develop opposite-

Answer 3

lumbar and upper sacral segment.

Question 4

Limb buds consist of-

Answer 4

– A mesenchymal core

– Covered by ectoderm

Question 5

wht starts off the process of limb

development ( elongation )

Answer 5

Activation of mesenchymal cells in the lateral

mesoderm

Question 6

Paraxial mesoderm-

Answer 6

• Divides into 42-44 pairs

of somites

Question 7

Intermediate mesoderm

Answer 7

• Urogenital system

Question 8

Lateral plate mesoderm

Answer 8

– Subdivision of the intraembryonic(secondary) mesoderm

– Forms the connective tissue of the limbs

Question 9

Somites give rise to-

Answer 9

Sclerotome,Myotome,Dermatome

Question 10

The Homeobox (HOX) gene initiates

Answer 10

Limb development

Question 11

Activation of mesenchyme induces formation-

Answer 11

of an apical ectodermal ridge (AER)

Question 12

Mesenchyme condenses and gives rise to -

Answer 12

skeleton & connective tissue

Question 13

Apical ectodermal ridge (AER)

Answer 13

– Ectodermal thickening at the apex of each limb bud

– Inductive influence on limb mesenchyme

Question 14

Progress zone (AER)

Answer 14

Stimulates proliferation of mesenchyme

Question 15

– Proximodistal axis (AER)

Answer 15

Growth and development of the limbs

Question 16

Proximodistal Axis -

Answer 16

Signaling Center - (AER)
Molecular Signal-Fibroblast growth
factors (FGF-2,-4,-8)

Question 17

Anteroposterior Axis

Answer 17

Signaling Center-Zone of polarizing
activity (ZPA)
Molecular Signal-Sonic hedgehog (Shh)

Question 18

Dorsoventral Axis

Answer 18

Signaling Center-Dorsal ectoderm + Ventral ectoderm

Molecular Signal- Wnt-7a (dorsal)+ En-1 (ventral)

Question 19

Limb Development – 28 days

Answer 19

Limb buds appear as small elevations of the ventrolateral body wall
– Upper limb buds appear by 26th – 27th day
• Opposite C5-T1 spinal segments (
– Lower limb buds appear ~2 days later
• Opposite L4–S3 spinal segments

Question 20

Limb Development – 32 days

Answer 20

Formation of hand and foot plates

Question 21

Limb Development -Week 6

Answer 21

Mesenchymal tissue in the hand plates condense to form digital ray ( finger
buds ), outlines the pattern of the digits
-– Tissue between digital rays
undergoes apoptosis

Question 22

Limb Development -Week 7

Answer 22

– Mesenchymal tissue in the foot plates condense to form digital ray ( toe
buds ), outlines the pattern of the digits.
– Tissue between digital rays undergoes apoptosis (programmed cell death )
• Forming notches between the digit rays

Question 23

Limb Development -Week 8 (56 days)

Answer 23

– Fingers and toes are distinct and separated

Question 24

Positional Changes of Developing Limbs-48 days

Answer 24

Limbs extend ventrally
– Hand plates & foot plates
face each other

Question 25

Positional Changes of Developing Limbs-51 days

Answer 25

Upper limbs bent at elbows | – Hands curved over thorax

Question 26

Positional Changes of Developing Limbs-54th day

Answer 26

Soles of feet face medially

Question 27

Positional Changes of Developing Limbs-56th day

Answer 27

--Elbows point caudally | – Knees point cranially

Question 28

Development of Cartilaginous Bones- 5th week

Answer 28

Chondrification centers

Question 29

Development of Cartilaginous Bones- 6th week

Answer 29

6th week, the entire limb | skeleton is cartilaginous

Question 30

Development of Cartilaginous Bones- 7th week

Answer 30

Osteogenesis of the long bones begins in the 7th week – Primary ossification centers

Question 31

Ossification of Appendicular Skeleton- Diaphysis

Answer 31

Formed by primary center of ossification | • Appear by 7th -8 th week

Question 32

Ossification of Appendicular Skeleton- Epiphysis

Answer 32

– Formed by secondary centers of ossification | • Appear during first 4 yrs

Question 33

Ossification of Appendicular Skeleton-Epiphyseal plate

Answer 33

``` - Growth plate between diaphysis and epiphysis – Adds length to the bone – Persist until growth period is over ```

Question 33

Ossification of Appendicular Skeleton-Epiphyseal plate

Answer 33

``` - Growth plate between diaphysis and epiphysis – Adds length to the bone – Persist until growth period is over ```

Question 34

Myotomes of Body Somites- Epaxial myotome

Answer 34

intrinsic muscles of back

Question 35

Myotomes of Body Somites- Hypaxial division

Answer 35

(ventral)

Question 36

when do the Sensory axons enter the limb buds-

Answer 36

Sensory axons enter limb buds after the motor axons , + Motor axons arise from the spinal cord & enter limb bud during the 5th week

Question 37

• Neural crest cells

Answer 37

-Precursors of Schwann cells – Surround motor and sensory nerve fibers in the limbs – Form the neurolemma and myelin sheaths

Question 38

Development of Limb Arteries-intersegmental arteries

Answer 38

– Arise from dorsal aorta – Form fine capillary network throughout mesenchyme

Question 39

Cutaneous syndactyly

Answer 39

– Webbing of the digits – failure of webs to degenerate | between 2 or more digits

Question 40

Osseous syndactyly

Answer 40

– Fusion of the bones – failure of development of notches | between the digital rays

Question 41

Polydactyly

Answer 41

* Supernumerary digits * Disruption of the anteroposterior pattern * Inherited as a dominant trait

Question 42

Club Foot (Congenital Talipes )

Answer 42

Talipes equinovarus ( is most common type ) • Twice more frequently in males as in females. • Sole of foot is turned medially and the foot is inverted. • Multifactorial pattern of inheritance.

Question 43

Amelia

Answer 43

Complete absence of limbs – Suppression of limb bud development in the 4th week

Question 44

Meromelia

Answer 44

Partial absence of limbs – Disturbance of limb development during 5th week

Question 45

Cleft Hand & Cleft Foot (Ectrodactyly)

Answer 45

Absence of one or more central digits – Failure of development of one or more digital rays • Remaining digits are partially or completely fused

Question 46

Amniotic Band Syndrome

Answer 46

ears in the amnion result in amniotic bands • May encircle fetal limbs & digits – Ring constrictions – Amputations

Question 47

VACTERL Syndrome

Answer 47

``` at least three of these characteristic features – Vertebral defects – Anal atresia – Cardiac defects – Tracheo-esophageal fistula – Renal anomalies – Limb abnormalities ```