KEY POINTS

1. Vascular resistance is affected by intrinsic and extrinsic control mechanisms.

2. Metabolic control of blood flow is a local mechanism that matches the blood flow of a tissue to its metabolic rate.

3. Autoregulation is a relative constancy of blood flow in an organ despite changes in perfusion pressure.

4. Many chemical signals act locally (as paracrines) to exert important control on vascular resistance.

5. Regardless of the status of arterioles, mechanical compression can reduce blood flow to a tissue.