[thedoc (OP)]

Claudio R. Cusin asked the Naked Scientists:
   
How do our cells know the exact direction to grow and to settle themselves in order to maintain the format of our bodies.  For example, I am 50 year old and, disregarding some minor variations, the shape and size of my nose, my lips and my hands remain largely unchanged since I was 30.  Since there are no "marked positions on the floor" what is the mechanism that guides the cell reproduction to maintain the formats of the bodies of any living being ?

What do you think?

[evan_au]

For already-differentiated cells, their position and role in the body is added onto their DNA as a series of epigenetic controls.

Even stem cells in a tissue are partially pre-programmed with the types of cells to which they can give rise.

Individual cells, when they divide, are influenced by the immediate environment in which they find themselves, and will try to "fit in".

In the case of wound healing, the damage is far larger than a single cell. It has been found that electrical gradients within the wound provide a macroscopic "direction", giving a more global orientation to the growth process, which is not visible in the immediate environment of a single cell.

So the cells of our bodies are influenced by both their genetics and their environment. (A bit like people, really...)