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

a. Blood flow through muscle contractionsb. Increased blood flow in muscle capillaries during

exercise

Fig. 21.1

Blood Flow Regulation in Skeletal Muscle

• Control of Blood Flow in Skeletal Muscles

a. Local regulation-decreased oxygen in muscle greatly enhances flow

b. Nervous control of muscle blood flow-sympatheticvasoconstrictor nerves

Blood Flow Regulation in Skeletal Muscle

•Total Body Circulatory Readjustments During Exercise

a. Effects of mass sympathetic discharge

1. Heart is stimulate to an increased rate and increasedpumping strength

2. Most of the arterioles of the peripheral circulationare contracted (except those of the active muscles)

3. 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

a. Increase in arterial pressure due to sympathetic stimulation

1. Vasoconstriction of the arterioles and small arteries in tissues other than the active muscles

2. Increased pumping activity of the heart3. 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

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

a. Phasic changes in coronary blood flow during systoleand diastole—effect of cardiac muscle compression

Fig. 21.4

Coronary Circulation (cont.)

b. 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

a. Oxygen demand is a major factor in local coronaryblood flow regulation

• Nervous Control of Coronary Blood Flow

a. Direct effects of nervous stimuli on the coronaryvasculature

b. Sympathetic greater effects than parasympathetic