Page 16, O2 Uptake, Exercise & Cor. Circ., Dr. D. Penney
Coronary Circulation (continued..):
The coronary vessels serve a number of functions: The epicardial arteries and veins act as passive conduits in the rapid mass transport of blood to and from the myocardium, but they can change caliber up to 50% when treated with vasoactive substances. These vessels are the primary sites of coronary artery disease. The intramural arteries are branches perpendicular to the epicardials and form a dense vascular network of smaller vessels in the wall. The intramural arterioles and pre-capillary sphincters are the sites of greatest vascular resistance.
The semi-permeable membrane constituting the capillaries, provides a diffusing surface of nearly 1,200 sq. cm per g of tissue (i.e. area 13 x 13 inches), permitting the rapid uptake and release of gases and metabolites.
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