■ FIGURE 7.6 Anterior view of the heart showing the major coronary arteries. The left main artery arises
from the aorta (Ao) just distal to the aortic valve, travels behind the pulmonary artery
and then
branches into the circum flex artery (courses along the left atrioventricular groove) and left anterior
descending artery (courses along the interventricular groove), both of which prim arily supply blood to
the left ventricle. The right coronary artery arises from the aorta and travels between the right atrium and
ventricle toward the posterior regions of the heart to supply the right ventricle and atrium and the infer-
oposterior wall of the left ventricle.
superior vena cava;
inferior vena cava.
individuals in the anatomical arrangement and
distribution of flow by the coronary vessels.
The major coronary arteries lie on the
epicardial surface of the heart and serve as
low-resistance distribution vessels. These epi-
cardial arteries give off smaller branches that
dive into the myocardium and become the
microvascular resistance vessels that regulate
coronary blood flow. The resistance vessels
give rise to a dense capillary network so that
each cardiac myocyte is closely associated
with several capillaries. The high capillary-
to-fiber density ensures short diffusion dis-
tances to maximize oxygen transport into the
cells and removal of metabolic waste products
(e.g., CO2, H+) (see Chapter 8).
Coronary veins are located adjacent to
coronary arteries. These veins drain into the
coronary sinus located on the posterior aspect
of the heart. Blood flow from the coronary
sinus empties into the right atrium. Some
drainage also occurs directly into the cardiac
chambers through the anterior cardiac veins
and thebesian vessels.
When flow is measured within an epicardial
coronary artery, it is found to decrease during
cardiac systole and increase during diastole
(Fig. 7.7). Therefore,
most of the blood flow
to the myocardium occurs during diastole.
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