Unit Four: The Circulation Chapter 21: Muscle Blood Flow and Cardiac Output During Exercise; Coronary Circulation and Ischemic Heart Disease Guyton and Hall, Textbook of Medical Physiology, 12 edition

Blood Flow Regulation in Skeletal Muscle Rate of Blood Flow Through the Muscles Blood flow through muscle contractions Increased blood flow in muscle capillaries during exercise Fig. 21.1

Blood Flow Regulation in Skeletal Muscle Control of Blood Flow in Skeletal Muscles Local regulation-decreased oxygen in muscle greatly enhances flow Nervous control of muscle blood flow-sympathetic vasoconstrictor nerves

Blood Flow Regulation in Skeletal Muscle Total Body Circulatory Readjustments During Exercise Effects of mass sympathetic discharge Heart is stimulate to an increased rate and increased pumping strength Most of the arterioles of the peripheral circulation are contracted (except those of the active muscles) Muscle walls of the veins are contracted which increases the mean systemic filling pressure

Blood Flow Regulation in Skeletal Muscle Total Body Circulatory Readjustments During Exercise Increase in arterial pressure due to sympathetic stimulation Vasoconstriction of the arterioles and small arteries in tissues other than the active muscles Increased pumping activity of the heart Great increase in mean systemic filling pressure

Blood Flow Regulation in Skeletal Muscle Importance of Increase in CO During Exercise Fig. 21.2 Graphic analysis of change in CO and right atrial pressure with onset of stenuous exercise Black curve is normal and red cure is strenuous exercise

Physiologic Anatomy of the Coronary Blood Supply Coronary Circulation Physiologic Anatomy of the Coronary Blood Supply Fig. 21.3 The coronary arteries

Coronary Circulation (cont.) Normal Coronary Blood Flow-- about 5% of CO Phasic changes in coronary blood flow during systole and diastole—effect of cardiac muscle compression Fig. 21.4

Coronary Circulation (cont.) Epicardial vs. subendocardial coronary blood flow— effect of intramyocardial pressure Fig. 21.5

Control of Coronary Blood Flow Local Muscle Metabolism is the Primary Controller Oxygen demand is a major factor in local coronary blood flow regulation Nervous Control of Coronary Blood Flow Direct effects of nervous stimuli on the coronary vasculature b. Sympathetic greater effects than parasympathetic