Читать книгу Understanding Anatomy and Physiology in Nursing - John Knight - Страница 115

Since the heart is continually active, the cardiac muscle fibres of the myocardium require a continual supply of highly oxygenated blood, and this is supplied via the coronary arteries (Figure 3.9). These are relatively small blood vessels originating directly from the aorta and located on the outer surface of the heart. The term coronary refers to the collective appearance of these vessels as resembling a crown that encircles the heart (corona is Latin for crown). The smaller coronary arteries are interconnected by tiny bridging channels termed anastomoses. Should a blockage (e.g. a clot or detached piece of fatty plaque) occur, blood can be diverted into these anastomotic (collateral) channels which can expand and widen, ensuring that the myocardium in proximity to the blockage remains perfused. The anastomotic nature of the coronary circulation allows small blockages to be effectively bypassed, increasing the chances of survival following an MI.

Although the coronary arteries only receive around 4 per cent of the total blood flow, the continually active myocardium is responsible for approximately 11 per cent of the body’s total oxygen consumption. This heavy demand for oxygen renders the myocardium susceptible to many factors which can compromise blood flow, particularly narrowing of the coronary vessels due to atherosclerotic occlusion.

Figure 3.9 The coronary arteries