Figure 3.

(a) A schematic of the cell–cell and cell–wall interaction forces. When cells are far from one another, they are assumed to have a negligible impact on each other's motion; as they move closer they exert an attractive force on one another, until their centres are very close and this force becomes repulsive. (b) A schematic of environmental forces in the system. Blood flow acts along the negative z-axis in this model and is opposed by a chemoattractive force along the main axis of the vessel due to the production of chemoattractants upstream of the plug (e.g. in the myometrium). Chemoattractants may also be released by cells in or near to the vessel wall, and thus a radial force due to these (potentially different) chemoattractants is also modelled. (Online version in colour.)