Lecture 19: Limb Development Flashcards
Which develops first? Lower limbs or upper limbs?
Upper Limbs develop first
In what week do the upper and lower limbs begin to develop?
Week 4
Why do the upper limbs develop slightly ahead?
Better blood supply due to the fact that the embryo favors supplying the brain - and therefore the upper half of the embryo - with blood.
When do the limb buds develop?
4th Week
What embryological structure gives rise to the muscle of the limbs?
The Hypomere (Pariaxial Mesoderm -> Somite -> Myotome -> Hypomere)
Where does the cartilage and connective tissue of the upper limb come from embryologically?
What does cartilage serve as a precursor for in the upper limb?
Somatic Lateral Plate Mesoderm
Bone
Where do the Fascia and Blood Vessels of the upper extremity come from?
Somatic Lateral Plate Mesoderm
(They are part of the Connective Tissue)
What is the “Limb Forming Mesoderm” made of?
Pariaxial and Somatic Lateral Plate Mesoderm
What stimulates the Surface Ectoderm to become the Apical Ectodermal Ridge?
FGF 10
What is the Apical Ectodermal Ridge made of?
Surface Ectoderm
The Apical Ectodermal Ridge is just a thickening of the surface ectoderm that was already there in response to FGF 10
What releases FGF 10?
The Limb - Forming Mesoderm
What releases FGF 4 and 8?
The Apical Ectodermal Ridge
What do FGF 4 and 8 do?
Stimulate growth of the Limb-Bud Mesoderm
What “fates” certain regions of the Limb-Forming Mesoderm to become certain bones?
Concentration gradients of signaling molecules.
What does the Stylopod give rise to?
Humerus and Femur
What does the Zeugopod give rise to?
Ulna/Radius
Tibia/Fibula
What does the Autopod give rise to?
Carpals/Metacarpals and Digits of the Hand
Tarsals/Metatarsals and Digits of the Foot
When do the Hand and Foot Plates Develop?
Week 5?
When do the Digital Rays of the Hand develop?
Week 6
When do the Digital Rays of the Feet develop?
Week 7
When do the limbs rotate?
Week 7
When do the long bones begin to ossify?
Week 7
When do we start to separate our digits?
Week 8
What pro-apoptotic family is responsible for separating our digits?
If these are down-regulated, what conditions might we see?
BMP’s
Webbed fingers or Syndactyly
When do Chondrification Centers appear?
Week 5
During Week 6, what is the status of the limb skeleton?
The entire limb skeleton is cartilage during Week 6.
In what region of the embryo is the limb bud forming?
The Cervical Region
In what region is the leg bud forming?
The Lumbosacral Region
When do Motor Axons from the spinal cord enter the limb buds?
Week 5
What gives rise to motor neurons?
Neural Tube (Neuroectoderm)
When is the Brachial Plexus formed in the embryo?
Week 5
When the Motor Neurons enter the Limb Bud
How do Sensory Neurons decide where they are going to develop?
They follow the Motor Neurons
What myelinates the neurons of the peripheral nervous system?
What gives rise to these?
Schwann Cells
Neural Crest Cells
Does the upper limb rotate Medially or Laterally?
Laterally (90°)
Does the lower limb rotate medially or laterally
Medial (90°)
What is the first branch from the Aorta that goes into the limb bud?
What does that structure immediately give rise to?
Intersegmental Arteries
Primary Axial Artery
What two arteries does the Primary Axial Artery of the Upper Limb become?
The Brachial Artery
Common Interosseous Artery
What happens to the Common Interosseous Artery and the Brachial Artery to make them form the adult structure?
Remodeling
What is the common name for Talipes Equinovarus?
Club Foot
What demographic is more likely to aquire Club Foot?
Males (Twice as likely)
What causes club foot? (2 causes)
Abnormal Limb Rotation
OR
Oligohydramnios
What demographic is susceptible to Developmental Hip Dysplasia?
More common in Females
What is Developmental Hip Dysplasia?
Under development of the Acetabulum of the “hip bone”
OR
Generalized joint laxity in the hip
What determines the position of the limbs along a cranial / caudal axis?
HOX genes
What determines the types and the shapes of bones?
HOX genes
What maintains the dorsal patterning for the upper limb?
Wnt7
I WNT a better name for the dorsal patterning signal
What maintains the ventral patterning for the upper limb?
BMPS
_B_li_mps_ (BMPS) have Vents
What determines the Posterior side of the upper limb?
The Zone of Polarizing Activity (ZPA)
The Zone of Polarizing Activity (ZPA) releases what two signaling molecules?
Retinoic Acid
Sonic Hedgehog
What can loss of ZPA cause?
Lack of Posterior Elements
(Like the little finger and the Ulna B.)
What causes Polydactyly?
Upregulation of ZPA
What might cause you to have pinky fingers on both the anterior and side of the hand?
Duplication of ZPA
Which are formed first, Posterior Elements or Anterior Elements?
Posterior Elements
In what week might the error that leads to polydactyly of the hands occur?
Week 6
In what week might the error that leads to syndactyly occur?
Week 8
(when apoptosis occurs)
When does primary ossification occur?
Week 12
When might the error that leads to Club Foot occur?
(Assuming it’s not due to Oligohydramnios)
Week 7
What disease was caused by Thalidomide?
What weeks were molested by the drug?
Meromelia
Weeks 3, 4, and 5
What might lead to syndactyly?
Downregulation of BMPs
What might lead to Ectrodactyly
What is Ectrodactyly?
Downregulation of the center of the Apical Ectodermal Ridge
Split Hand / Lobster Claw
What is Arthrogryposis?
Congenital Joint Contracture
