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Limb Development - Anatomy & Physiology (view source)
Revision as of 19:09, 29 August 2008
, 19:09, 29 August 2008no edit summary
===Proximal - Distal Patterning===
===Proximal - Distal Patterning===
*Governed by the PZ.
*The first cells to leave the PZ have a proximal identity.
*These cells have been in the PZ for a shorter amount of time than those that leave the PZ last, which have a distal identity.
*"Identity" is achieved by the HOX - A gene expression.
**Cells that leave the PZ early have fewer HOX - A genes expressed than those which leave later.
**Less HOX - A gene expression results in a more proximal cell appearance.
===Anterior - Posterior Patterning===
===Anterior - Posterior Patterning===
*Important in producing the correct number of digits that are of the correct morphology.
*An area of mesenchyme exists adjacent to the AER, in the posterior of the distal limb called the '''zone of polarising activity (ZPA)'''.
*The ZPA produces a '''morphogen'''(substance that induces other cells to change).
**This morphogen works in a ''dose - dependant'' manner.
**The morphogen diffuses to form a concentration gradient and has different effects on cells depending on it's concentration.
**Higher concentrations of this morphogen produces posterior digits.
***Posterior digits have more cells than anterior cells.
***The more cells, the more morphogen produced.
***The more morphogen, the more posterior the digits.
*Polydactly is common in animals, and is due to
===Dorsal - Ventral Patterning===
===Dorsal - Ventral Patterning===