Development of the Upper and Lower Limb Flashcards
When do Upper limb buds + lower limb buds appear
Upper limb buds-day 26 or 27,
lower limb buds- 1 or 2 days later.
Upper limb buds develop opposite -
he caudal cervical segment,
lower limb bud develop opposite-
lumbar and upper sacral segment.
Limb buds consist of-
– A mesenchymal core
– Covered by ectoderm
wht starts off the process of limb
development ( elongation )
Activation of mesenchymal cells in the lateral
mesoderm
Paraxial mesoderm-
• Divides into 42-44 pairs
of somites
Intermediate mesoderm
• Urogenital system
Lateral plate mesoderm
– Subdivision of the intraembryonic(secondary) mesoderm
– Forms the connective tissue of the limbs
Somites give rise to-
Sclerotome,Myotome,Dermatome
The Homeobox (HOX) gene initiates
Limb development
Activation of mesenchyme induces formation-
of an apical ectodermal ridge (AER)
Mesenchyme condenses and gives rise to -
skeleton & connective tissue
Apical ectodermal ridge (AER)
– Ectodermal thickening at the apex of each limb bud
– Inductive influence on limb mesenchyme
Progress zone (AER)
Stimulates proliferation of mesenchyme
– Proximodistal axis (AER)
Growth and development of the limbs
Proximodistal Axis -
Signaling Center - (AER)
Molecular Signal-Fibroblast growth
factors (FGF-2,-4,-8)
Anteroposterior Axis
Signaling Center-Zone of polarizing
activity (ZPA)
Molecular Signal-Sonic hedgehog (Shh)
Dorsoventral Axis
Signaling Center-Dorsal ectoderm + Ventral ectoderm
Molecular Signal- Wnt-7a (dorsal)+ En-1 (ventral)
Limb Development – 28 days
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
Limb Development – 32 days
Formation of hand and foot plates
Limb Development -Week 6
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
Limb Development -Week 7
– 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
Limb Development -Week 8 (56 days)
– Fingers and toes are distinct and separated
Positional Changes of Developing Limbs-48 days
Limbs extend ventrally
– Hand plates & foot plates
face each other
Positional Changes of Developing Limbs-51 days
Upper limbs bent at elbows
– Hands curved over thorax
Positional Changes of Developing Limbs-54th day
Soles of feet face medially
Positional Changes of Developing Limbs-56th day
–Elbows point caudally
– Knees point cranially
Development of Cartilaginous Bones- 5th week
Chondrification centers
Development of Cartilaginous Bones- 6th week
6th week, the entire limb
skeleton is cartilaginous
Development of Cartilaginous Bones- 7th week
Osteogenesis of the long
bones begins in the 7th
week
– Primary ossification centers
Ossification of Appendicular Skeleton- Diaphysis
Formed by primary center of ossification
• Appear by 7th -8 th week
Ossification of Appendicular Skeleton- Epiphysis
– Formed by secondary centers of ossification
• Appear during first 4 yrs
Ossification of Appendicular Skeleton-Epiphyseal plate
- Growth plate between diaphysis and epiphysis – Adds length to the bone – Persist until growth period is over
Ossification of Appendicular Skeleton-Epiphyseal plate
- Growth plate between diaphysis and epiphysis – Adds length to the bone – Persist until growth period is over
Myotomes of Body Somites- Epaxial myotome
intrinsic muscles of back
Myotomes of Body Somites- Hypaxial division
(ventral)
when do the Sensory axons enter the limb buds-
Sensory axons enter limb buds after the motor axons , + Motor axons arise from the spinal cord & enter limb
bud during the 5th week
• Neural crest cells
-Precursors of Schwann cells
– Surround motor and sensory nerve fibers in the limbs
– Form the neurolemma and myelin sheaths
Development of Limb Arteries-intersegmental arteries
– Arise from dorsal aorta
– Form fine capillary network
throughout mesenchyme
Cutaneous syndactyly
– Webbing of the digits – failure of webs to degenerate
between 2 or more digits
Osseous syndactyly
– Fusion of the bones – failure of development of notches
between the digital rays
Polydactyly
- Supernumerary digits
- Disruption of the anteroposterior pattern
- Inherited as a dominant trait
Club Foot (Congenital Talipes )
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.
Amelia
Complete absence of limbs
– Suppression of limb bud
development in the 4th week
Meromelia
Partial absence of limbs
– Disturbance of limb
development during 5th week
Cleft Hand & Cleft Foot (Ectrodactyly)
Absence of one or more central digits
– Failure of development of one or more digital rays
• Remaining digits are partially or completely fused
Amniotic Band Syndrome
ears in the amnion result in amniotic bands
• May encircle fetal limbs & digits
– Ring constrictions
– Amputations
VACTERL Syndrome
at least three of these characteristic features – Vertebral defects – Anal atresia – Cardiac defects – Tracheo-esophageal fistula – Renal anomalies – Limb abnormalities
