Describe the adult coronary circulation (50% of marks).
Describe the physiological control of the coronary circulation (50% of marks).
For a good pass candidates were expected to cover at least the following areas -
Anatomy of the coronary arteries and their supply, variations in supply and venous
Other unique features - coronary sinus saturation <30%, the diastolic aortic pressure,
Tachycardia reduces the coronary blood flow through a reduction in diastolic time, left
ventricle perfused mainly during diastole and right ventricle perfused mainly during systole,
different pattern of left and right ventricular coronary perfusion (drawing a figure of Rt and
Lt coronary blood flow), lack of capacity for the myocardium to increase its extraction ratio
Physiological control: The most important mechanism through which coronary blood flow
can be changed is by autoregulation which changes the coronary vascular resistance to
maintain constant flow in response to different coronary perfusion pressure and changing
metabolic demand. Important mediators are adenosine, nitric oxide, and opening of the ATPsensitive
K+ channels, prostaglandins, carbon dioxide, lactic acid or hydrogen ion.
Sympathetic stimulation to heart increases coronary blood flow.
Overall the greatest deficiency by candidates was lack of detail, use of illustrations and
clarity in their response. It is important that candidates take note of the distribution of marks
given within the question.
Reference Text: Berne and Levy Cardiovascular Physiology Chapter 11 Coronary circulation.
Adult coronary circulation:
Physiological control of coronary circulation:
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