Animation of the colon crypt.

Cell growth and division occurs near the bottom of the crypt. This displaces the non-growing cells, and the cells are sloughed off when they reach the end of the crypt. The lifetime of a cell in a crypt is ~ 5 days. The cell cycle time of a dividing cell is ~ 1 day. There are about 25 cells per crypt at any given time. In this model, there is one stem cell, at the bottom of the line of cells in the animation. The simplest way to make the animation, in which cells divide exactly in two and grow at the same rate makes a "mechanical-looking" animation. Some jitter was added in the division (one cell is usually somewhat bigger than the other) and in the growth rate. Also, the growth rate was made exponential (dependent on the present cell size) rather than uniform in time. (experimental data: crypt is 100 microns long, the mitotic zone is the bottom 40 microns, the "mitotic fraction" is ~1 at any given time, lifetime of cells in the crypt is ~5 days)

Version 1 - variable growth zone, tracking sister cells, determination of lifetime within the crypt. Version 2 - more polished looking animation, but no ability to change growth zone. The crypt is actually a cylinder, and if it is sliced along the long axis and laid out as a planar layer of cells, this is what it should look like - Version 3