Geometry, Structure, and Mechanics of Resistance Arteries

The function of resistance arteries is to control the flow of blood. The more proximal resistance arteries (normally termed small arteries) appear to control the extent of perfusion of the different organs of the body. The role of the more distal resistance arteries (normally termed arterioles; that is, those arteries having not more than one complete layer of smooth-muscle cells) is to regulate the supply of blood within organs. In both cases, function is mediated through control of artery diameter and thus resistance. Resistance is determined by the lumen/pressure relationship, a relation often referred to as the “distensibility” of the artery.’ This relationship is thus perhaps the most important characteristic of a small artery. However, it is complex: it is dependent on the amount, arrangement, and characteristics of the connective tissue and smooth-muscle cells, and is also determined by the activation level of the smooth-muscle cells. This is influenced by the intravascular pressure. This chapter will consider the role of resistance-arterynetworks29-31 By avoiding the need to include every vessel in the analysis, new sampling methods32 raise the possibility of making unbiased estimates of the mean values of many of these parameters more easily.