The circulatory system carries various oxygen, substrates, and chemical messengers; removes carbon dioxide and metabolic byproducts; assists with thermoregulation; and is an important mediator for acid-base balance.1 Blood consists of fluid and cellular components. Blood plasma is the liquid portion of blood and consists of water, proteins, electrolytes, dissolved gases, and nutrients.1 The cellular constituents consist of erythrocytes, leukocytes, and platelets. Oxygen and carbon dioxide (discussed in the next section) dissolve to a limited extent in blood plasma, but are largely carried bound to hemoglobin found in erythrocytes. The heart serves to pump blood to the pulmonary and peripheral circulation. Resting heart rate is approximately 80 beats per minute for a large dog.1 In response to exercise, heart rate and myocardial contractility increase, which concomitantly increases cardiac output. A large dog typically has increases of 30% for stroke volume, 300% for heart rate, and approximately 400% for cardiac output during vigorous exercise when compared with rest.1
Basics of Exercise Physiology
Figure 8-1 Work capacity increases when physical stress increases and adequate time allows for adaptation.
Cardiopulmonary Physiology
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Basics of Exercise Physiology
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