The heart provides bulk flow of blood to the various tissues of the body, contracting approximately 21/2 billion times during the lifetime of a human. Compared with other organs, the heart has high basal oxygen consumption (8 to 10mL 02/min/100g) and a large A-VO2 difference (10 to 13 mL/100mL). The resistance arterioles (and to a far lesser extent the large coronary arteries) are responsible for mediating vasomotor tone and blood flow. Coronary flow is closely matched to metabolic demands and myocardial oxygen consumption. The precise mechanisms that couple oxygen demand with blood flow remain unknown. Several factors appear to be important, including metabolic changes (termed metabolic dilation), flow characteristics, and fluctuations in intramural pressure. Each of these factors is differentially regulated in space and time. For example, metabolic-mediated changes in arteriole diameter and blood flow depend, at least in part, on the initial diameter of the vessel and location within the myocardial wall. The arterial system in the human heart is interconnected by collateral vessels that can enlarge and rescue ischemic areas of myocardium.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.