Changes

==Limb Bud Formation==

==Limb Bud Formation==

 

The limbs begin as lateral proliferations of the mesenchymal lateral plate mesoderm covered by ectoderm. The lateral plate mesoderm proliferates in a lateral direction along the entire midline, but then stops at the region of the interlimb (area between the limbs).

*The limbs begin as lateral proliferations of the mesenchymal lateral plate mesoderm covered by ectoderm.  

This produces small buds, which will continue to grow and eventually form the limbs. Proliferation of the lateral plate mesoderm cannot sustain entire limb growth; instead the '''apical ectodermal ridge (AER)''' maintains growth. The AER develops as mesenchymal cells in the distal limb ectoderm that has locally thickened by changing their morphology from cuboidal to columnar. It divides the limb into dorsal and ventral halves. The ridge can be seen when looking at the limb bud in a distal to poximal direction. The AER maintains an area of rapidly proliferating cells beneath it, called the '''progress zone (PZ)'''. The rapidly increasing number of cells drives the limb bud out distally, elongating the limb. As cells leave the PZ they differentiate.

**The lateral plate mesoderm proliferates in a lateral direction along the entire midline, but then stops at the region of the interlimb (area between the limbs).

**This produces small buds, which will continue to grow to eventually form the limbs.

*Proliferation of the lateral plate mesoderm cannot sustain entire limb growth; instead the '''apical ectodermal ridge (AER)''' maintains growth.

**The AER develops as mesenchymal cells in the distal limb ectoderm that has locally thickened by changing their morphology from cuboidal to columnar.

**It divides the limb into dorsal and ventral halves.

**The ridge can be seen when looking at the limb bud in a distal to poximal direction.

*The AER maintains an area of rapidly proliferating cells beneath it, called the '''progress zone (PZ)'''.

*The rapidly increasing number of cells drives the limb bud out distally, elongating the limb.

*As cells leave the PZ they differentiate.

==Patterning of the Limb==

==Patterning of the Limb==