Fig. 7.

A. Diagram to show how the epithelial bridges could exert tension on the blood capillaries and prevent their collapse. The direction of the tension is indicated by the arrows. The bridges might also resist enlargement of the capillaries thus reducing the hoop stress in the wall. Modified from West (2009). B. Diagram showing how the junctions between the epithelial cells and the capillary wall could reduce the wall hoop stress just as the iron hoops do the same around a barrel of beer. In this diagram, the junction of the epithelial cell with the capillary wall runs around the circumference of a capillary. In Figure 7A, the junction is shown running along the direction of the axis of the capillary. These drawing show the two extremes of directions. In practice, the junctions presumably have a random orientation.