Resistance also influences total blood flow. Resistance is defined as the amount of friction the blood experiences as it travels through the blood vessels. Blood flow is always opposed by resistance. Friction is due to the contact between blood and the blood vessel wall. The term peripheral resistance is typically used when discussing the resistance of blood in the blood vessels (as opposed to the resistance of blood in the heart). Several factors affect this friction, including blood viscocity , blood vessel length , and the size of the lumen of blood vessels (as indicated by vessel radius).
