How experiments on single capillaries help us to understand the circulation as a whole.

ABSTRACT

After a brief summary of the discovery of the microcirculation, this review looks at two classical series of papers published during the first 30 years of the 20th century by Krogh and Landis, and then discusses how, over the last 30 years of the century, some of these ideas have been developed by experiments on single microvessels. The topics covered include the recruitment of capillaries during functional hyperaemia, the identification of pressure gradients in the circulation and hence the sites of vascular resistance, the confirmation of Starling’s principle of fluid exchange and the development of new ideas about microvascular fluid exchange and, how the phenomenon of flow sensitive permeability to small diffusible molecules has been discovered.