Introduction: a brief history of capillaries and some examples of their apparently strange behaviour

1. Over the past decade, evidence has accumulated challenging the notion that the smallest blood vessels, the capillaries, are static, uniform, semipermeable pipes with no function except as a passive barrier marking the boundary between the vascular compartments from the tissue compartment. 2. Instead, capillaries are dynamic structures that participate in the active regulation of water, waste and nutrient exchange, the formation and destruction of exchange vessels and the sites for initiation of signals to regulate the flow of blood into the exchange vascular network. 3. The following papers will provide insight into the expanded appreciation of the varied nature of capillaries and how their functions are co-ordinated to achieve 'whole organ' exchange.