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