Limb Development Flashcards
For the upper limb, describe Prexial and Postaxial
Preaxial is thumb and radius
Postaxial is pinky and ulna
What week do limb buds begin forming?
Week 4
What week do digits begin forming?
Week 8
Primary ossification centers form during which week?
Week 12
Muscles of limbs come from what?
Cartilage of the limbs and connective tissue come from what?
Somite mesoderm
Somatic lateral plate mesoderm
In the limb, the mesoderm releases what factor to stimualte the surface ectoderm to induce the formation of the Apical Ectodermal Ridge?
What does the AER give off?
FGF10
Limb bud
As the Apocal Ectodermal ridge forms it grows in what direction?
Proximally to Distally
What is the stylopod?
Humerus
Femur
What is the zeugopod?
Radius and Ulna
Tibia and Fibula
What do autopods become?
Carpels, Metacarpals, Digits
Tarsals, Metatarsals, Digits
What week do hand and foot plates appear?
What week do chondrification centers appear?
Week 5
Digital rays of the hands, and the entire limb skeleton (cartilagenous) appears at what week?
Week 6
What week do the digital rays of the feet, and osteogenesis of long bones begin?
Week 7
What week does rotation of the limbs occur?
Week 7
What week do seperate digits form through apoptosis?
What signalling factor is responsible for this digital apoptosis?
Week 8
BMP
Why is it that upper limbs form before lower limbs?
Blood supply is being shunted to the brain, and upper limbs are closer to this supply (i.e. more nutrients)
Describe the direction of rotation of limbs that occurs during Week 7?
Upper Limbs vs Lower Limbs
Upper limbs rotate 90 degrees Laterally
Lower limbs rotate 90 degrees Medially
Nerves start innervating the developing muscles at what week?
Week 5
Muscles of the limbs are derived from what portion of the somites?
A. Ventrolateral
B. Ventromedial
C. Dorsolateral
D. Dorsomedial
Dorsolateral
Motor axons from the spinal cord enter the limb buds during the 5th week, and are derived from what?
Neuralectoderm
Sensory neurons come from ________ and use ________ as a guidance.
Sensory neurons come from neural crest and use motor axons as a guidance.
At week 5 upper and lower limbs start growing out in what direction?
Laterally and caudally
(out and down)
At week 6, upper and lower limbs bend in what direction?
Anteriorly
Is Barber pole rotation is seen in the upper or lower limb?
Lower limb
What artery comes off the dorsal aorta and supplies the upper limb buds?
What artery does it become within the limb bud?
Intersegmental arteries from the dorsal aorta
Becomes the primary axial artery
The primary axial artery in the upper limb later becomes what structure?
The primary axial artey of the lower limb becomes what structure?
Upper limb: brachial artery
Lower limb: deep artery of the thigh
What is the most common musculoskeletal defect?
What is the presentation
Club foot or Talipes Equinovarus
Sole of foot is turned medially with foot inverted
Which of the following is true in Developmental Hip Dysplasia?
A. More common in females than males
B. Caused by under development of acetabulum of the hip bone
C. Caused by generalized joint laxity
D. All of the above
All of the above
A. More common in females than males
B. Caused by under development of acetabulum of the hip bone
C. Caused by generalized joint laxity
Positioning and shape of the limbs is regulated by turning what signalling molecule on and off?
Hox genes
Proximal to distal growth and patterning of the limbs is determined by what?
Describe the signaling cycle that occurs
Apical Ectodermal Ridge
FGF10 released by mesenchyme to AER
AER release of FGF-8 and FGF-4 to mesoderm
this is how we get the stylopod, zeugopod, and autopods
Dorso-ventral patterning also involves the AER, but instead two other signalling factors specific to dorsal or ventral side. What is the signalling factor for the dorsal surface, and what is the signalling factor for the ventral surface?
VEntral surface: BMPs
Dorsal Surface: Wnt7
Anterior (preaxial) and posterior (post-axial) patterning of the limb is established by what structure?
What side of the limb does this structure work on?
What signalling factors are involved?
Zone of Polarizing Activity works on the Posterior side and releases Shh and retinoic acid
Loss of ZPA would result in which of the following?
A. Additional posterior elements (polydactyly)
B. Loss of posterior elements
C. Duplication of posterior elements (little fingers on both sides of the thumb)
Loss of posterior elements
Upregulation of ZPA signals retionoic acid and Shh results in what?
A. Additional posterior elements (polydactyly)
B. Loss of posterior elements
C. Duplication of posterior elements (little fingers on both sides of the thumb)
Additional posterior elements (polydactyly)
T/F: Posterior elements like little finger and ulna are formed prior to anterior elements like thumb and radisu
True
What is the mechanism of this disease?
What week would this happen?
Upregulation of the ZPA
Week 6 (formation of the digital rays of the hand)
What is the mechanism of this disease?
What week does this occur?
Duplication of ZPA
Week 7 (formation of digital rays of foot plate)
Shown below are two defects on the left structure.
What is the name of both abnormalities?
What is the cause of the one specific to this lecture?
When does this issue occur?
Syndactyly: problem of BMP regulation
Week 8
Brachydactyly
Pictured below is a form of miromelia, called Phocomelia where hands/feet attach close to the body.
What is the mechanism of this abnormality?
In what week does it occur
Problem with FGF signalling and the Apical Ectodermal Ridge
Week 4 - Week 8
Happens between Week 4-week 8 because proximal to distal growth occurs during this time
What is the disease pictured below?
In what week does this abnormality develop?
Amelia
Week 4: a limb bud wasn’t even developed for upper limbs
problem with Apical ectodermal ridge
What is the name of the abnormality pictured below?
What is the mechanism of this abnormality?
Ectodactyly or Forked Hand/Foot
Center of the AER did not develop properly
