The final differentiated state of a cell is defined by the events it has experienced throughout development. In some organisms such as Cenorhabditis elegans the fate of some cells is determined at the start of cleavage while the rest of the cells are determined by cellular interactions that occur throughout development. In this organism it is possible to determine exactly which embryonic cell will become what differentiated cell came in the adult. The lineage of each cell is clearly defined. This is not the case in human cells. Their fate is not predetermined to any significant degree. The fate of cells is progressive being determined almost entirely by cellular contacts and by molecules secreted by other cells among other things. However by gastrulation, certain tissues have been formed, each of which will give rise in the normal course of events to specific cells, tissues and organs. By neurulation, even more tissue fates have been specified. The following figure shows the major tissues that exist in the fetus just after neurulation and what they will differentiate into.

This information was provided by Professor Danton H. O'Day - Univerisity of Toronto at Mississauga - Canada. Unless otherwise stated the information and graphics that are presented within this embryology section are the sole property of Danton H. O'Day, copyright 1998(c), 1999(c), 2000(c), 2001(c), 2002(c).

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