Vertebrate Limb Flashcards
What are the 3 main structures of the vertebrate limb?
- Stylopod
- Zeugopod
- Autopod
How many muscles and how many bones are in the vertebrate limb?
> 30 bones.
>50 bones.
What is the incidence of congenital limb abnormalities?
1 in 500.
What is ulna dimelia?
Involves a mirror image duplication within the developing hand, the individual has 8 digits, 2 little fingers, no equivalent to the thumb, the bones in the hand and wrist are in the mirror image orientation.
What are the 3 developmental axis of the limb?
- Anteroposterior
- Dorsoventral
- Proximodistal
Describe the anteroposterior axis of the developing limb?
The thumb is defined as being anterior and the little finger as being the posterior-most digit.
Describe the dorsoventral axis of the developimg limb?
At rest, the palm is ventral and the back of the hand is dorsal.
Describe the proximodistal axis of the developing limb?
The proximodistal axis runs from shouder/hip (being proximal) to fingers/toes (being distal).
The proximodistal axis is divided into 3 regions, the stylopod, the upper part of the limb from shoulder to ellbow, this has one major bone, the humerus or equivalent. The zeugopod is the lower part of the limb from the elbow to wrist typically with two bones, the radius and ulna or their equivalent. The autopod is where the digits are.
Describe the stylopod?
The stylopod is the upper part of the limb from shoulder to elbow/hip to knee with one major long bone, the humerus or the equivalent.
Describe the zeugopod?
The zeugopod is the lower part of the limb from elbow to wrist, typically with two bones, the ulna and radius or their equivalent.
What is the limb bud?
The limb bud is simply a jacket of ectodermal cells and underlying those ectodermal cells are mesenchyme cells (mesodermal cells). Limb buds first appear 24-26 days post-fertilisation.
Describe the limb bud organisation?
The limb bud is very small, perhaps 1mm from top to bottom, from anteroposterior and from proximal to distal.
There is ectoderm on the outside and mesenchyme derived from mesoderm on the inside.
The leading edge has the apical ectodermal ridge, a key signalling centre.
Behind this there is a set of mesenchymal cells that are relatively undifferentiated and rapidly dividing, this is the progress zone.
Behind this, there are some cells that aren’t dividing as rapidly and are beginninng to differentiate.
What is the progress zone?
A region of relatively undifferentiated and rapidly dividing cells responsible for limb bud outgrowth.
What is the size of the progress zone?
0.3mm from distal to proximal end.
What happens to the cells that have left the progress zone?
The cells that have left the progress zone aren’t dividing as rapidly anymore and are beginnng to differentiate.
