Assoc. Prof. MUDr. Markéta Bébarová, Ph.D.
Department of Physiology, Faculty of Medicine, Masaryk University
Coronary Circulation
This presentation includes only the most
important terms and facts. Its content by
itself is not a sufficient source of
information required to pass the
Physiology exam.
Coronary Circulation
• a. cor. sinistra
85% of the blood flow
(the frontal part of septum, the conductive system,
majority of the left ventricle)
• a. cor. dextra
(the right ventricle, the posterior part of septum and
usually also the posterior part of the left ventricle)
Ganong´s Review od Medical
Physiology, 23rd edition
• placing of coronary arteries and
capillaries in the cardiac walls
• O2 diffusion directly from the blood
situated in the cardiac cavities
Coronary Circulation
Guyton and Hall.
Textbook of Medical
Physiology, 11th edition
• epicardial coronary arteries supply most of the muscle
• intramuscular arteries (smaller) penetrate the muscle
• plexus of subendocardial arteries
• During systole, blood flow through the plexus of
subendocardial arteries is reduced (compression of
intramuscular arteries) – compensated through extra
vessels in the plexus (sensitivity to coronary ischemia).
Coronary Circulation
• a. cor. sinistra
85% of the blood flow
(the frontal part of septum, the conductive system,
majority of the left ventricle)
• a. cor. dextra
(the right ventricle, the posterior part of septum and
usually also the posterior part of the left ventricle)
Ganong´s Review od Medical
Physiology, 23rd edition
• coronary angiography
• placing of coronary arteries and
capillaries in the cardiac walls
• O2 diffusion directly from the blood
situated in the cardiac cavities
Coronary Circulation
http://pochp.mp.pl/aktualnosci/show.html?id=55102
Coronary Circulation
Ganong´s Review od Medical Physiology, 23rd edition
• during the systole, vessels
situated intramurally are
pressed by the contracting
myocardium
• left vs. right ventricle
• high heart rate
Coronary Circulation
• orificia of the coronary arteries
ejection
isovolumic
relaxation
Coronary Circulation
• O2 extraction is almost maximal already at rest,
capillaries are open
• The only possibility how to increase O2 supply
(for example during exercise) is the coronary
vasodilation!
Coronary Circulation
Control of coronary blood flow
1) reduction/interruption of the blood flow or
increased demands (exercise, increased blood pressure)
hyperaemia (reactive or active) based on the
metabolic vasodilation
mediators: pO2, pCO2, pH, [K+]e, adenosine,
bradykinin, prostaglandins, NO
Coronary Circulation
Control of coronary blood flow
2) the neural regulation of the vessel diameter –
secondary impact
a) indirect effects
b) direct effects
(mostly opposite)X
Coronary Circulation
Control of coronary blood flow
2) the neural regulation of the vessel diameter –
secondary impact
a) indirect effects
sympathetic system (NE, E)
parasympathetic system (ACH)
↑ HR + contractility → rate of cardiac metabolism →
increased O2 consumption → activation of local
vasodilating mechanisms
opposite changes → vasoconstriction
Coronary Circulation
Control of coronary blood flow
2) the neural regulation of the vessel diameter –
secondary impact
a) indirect effects
b) direct effects
sympathetic system (NE, E)
parasympathetic system (ACH)
epicardial vessels – mostly α-rec. → vasoconstriction
vasodilation, but not significant (only few fibers)
intramural vessels – mostly β-rec. → vasodilation
vasospastic
myocardial ischemia
Coronary Circulation
Control of coronary blood flow
2) the neural regulation of the vessel diameter –
secondary impact
a) indirect effects
b) direct effects
Whenever the direct effects alter the
coronary blood flow in the wrong direction,
the metabolic control overrides them
within seconds!
Coronary Circulation
• the resting blood flow: 225 ml/min (4-5% of CO)
• at physical exertion:
- cardiac output increased 4-7fold
- higher afterload
cardiac work may
increase 6-9fold
- coronary blood flow increases only 3-4fold!
- efficiency of the cardiac utilization of energy has to
increase to make up for the relative deficiency of
coronary blood supply
Cardiac Muscle Metabolism
• at rest: 70% of energy – fatty acids
• anaerobic/ischemic conditions: anaerobic glycolysis
high glucose consumption + high quantities of formed
lactic acid (one of causes of the ischemic pain + pH)
lost adenosine replaced by new synthesis of adenine,
but very slowly (2% per hour)
• severe ischemia: degradation of ATP to ADP, AMP
and, finally, to adenosine → loss of adenosine into
circulation through sarcolemma → vasodilation
Major cause of death of cardiomyocytes during
ischemia is the adenosine deprival! (30 min of severe
ischemia may cause irreversible changes and cell death)
Coronary Reserve
• ability of coronary vessels to adapt blood flow to the
actual cardiac work (ergometry)
• the maximal blood flow / the resting blood flow
• reduction of the coronary reserve:
- relative coronary insufficiency
(too high resting demands, high resting blood flow cannot be sufficiently
increased)
- absolute coronary insufficiency ( coronary
heart disease)
(the stenotic arteriosclerotic process)
Reduced coronary reserve is a limiting factor of the
cardiac output, thus, also of the effort of organism!