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M04.03.13 Cardiac muscle circulation
Cardiac muscle circulation refers to the blood supply to the heart muscle (myocardium) itself, primarily provided by the coronary arteries. This circulation is crucial for the heart’s function, as it ensures that the heart muscle receives the oxygen and nutrients necessary for its constant, rhythmic contractions.
1. Anatomy of Coronary Circulation
Coronary Arteries:
- Left Coronary Artery (LCA):
- Left Anterior Descending (LAD) Artery: Supplies the anterior part of the interventricular septum and the anterior walls of both ventricles.
- Circumflex Artery (Cx): Supplies the left atrium and the lateral and posterior surfaces of the left ventricle.
- Right Coronary Artery (RCA):
- Right Marginal Artery: Supplies the right ventricle.
- Posterior Descending Artery (PDA): Supplies the posterior part of the interventricular septum and the posterior walls of both ventricles.
Coronary Veins:
- Great Cardiac Vein: Drains the areas supplied by the LAD.
- Middle Cardiac Vein: Drains the posterior part of the heart.
- Small Cardiac Vein: Drains the right atrium and right ventricle.
- Coronary Sinus: Collects blood from the coronary veins and empties into the right atrium.
| Artery | Supplied Area |
|---|---|
| Left Anterior Descending (LAD) | Anterior interventricular septum, anterior walls of both ventricles |
| Circumflex Artery (Cx) | Left atrium, lateral and posterior surfaces of the left ventricle |
| Right Coronary Artery (RCA) | Right atrium, right ventricle |
| Posterior Descending Artery (PDA) | Posterior interventricular septum, posterior walls of both ventricles |
| Vein | Drained Area |
|---|---|
| Great Cardiac Vein | Areas supplied by the LAD |
| Middle Cardiac Vein | Posterior part of the heart |
| Small Cardiac Vein | Right atrium, right ventricle |
| Coronary Sinus | Collects from coronary veins, empties into right atrium |
2. Physiology of Coronary Blood Flow
Characteristics:
- Coronary blood flow primarily occurs during diastole when the heart muscle is relaxed.
- During systole, the coronary arteries are compressed by the contracting heart muscle, reducing blood flow.
Regulation of Coronary Blood Flow:
- Metabolic Regulation: Increased myocardial demand for oxygen leads to the production of metabolites (e.g., adenosine), causing vasodilation.
- Autoregulation: The coronary vessels can maintain a constant flow despite changes in perfusion pressure.
- Neural Control: Sympathetic stimulation increases heart rate and contractility, indirectly increasing coronary blood flow through metabolic mechanisms.
- Hormonal Control: Hormones like epinephrine cause vasodilation and increase coronary blood flow.
| Factor | Effect on Coronary Blood Flow |
|---|---|
| Diastole | Increased flow |
| Systole | Decreased flow |
| Metabolites (e.g., adenosine) | Vasodilation, increased flow |
| Sympathetic Stimulation | Increased flow via metabolic demand |
| Epinephrine | Vasodilation, increased flow |
3. Pathophysiology of Coronary Circulation
Coronary Artery Disease (CAD):
- Atherosclerosis: Build-up of plaques in coronary arteries leading to reduced blood flow.
- Angina Pectoris: Chest pain due to transient ischemia.
- Myocardial Infarction (MI): Heart attack caused by prolonged blockage of a coronary artery, leading to myocardial cell death.
Ischemia-Reperfusion Injury:
- Occurs when blood supply returns to the tissue after a period of ischemia or lack of oxygen. Can cause further damage due to oxidative stress and inflammation.
| Condition | Description |
|---|---|
| Atherosclerosis | Plaque build-up in coronary arteries |
| Angina Pectoris | Chest pain from transient ischemia |
| Myocardial Infarction | Heart attack due to prolonged blockage |
| Ischemia-Reperfusion Injury | Damage upon restoring blood flow after ischemia |
Key Points to Remember
- The heart’s blood supply is critical for its function and is provided by the coronary arteries.
- Coronary blood flow is highest during diastole.
- Regulation of coronary blood flow is multifactorial, involving metabolic, neural, and hormonal influences.
- Pathologies such as atherosclerosis, angina, and myocardial infarction can severely impact coronary circulation.
Bibliography
- Braunwald, E. (2018). Heart Disease: A Textbook of Cardiovascular Medicine. 11th ed. Philadelphia: Elsevier.
- Klabunde, R. E. (2011). Cardiovascular Physiology Concepts. 2nd ed. Philadelphia: Lippincott Williams & Wilkins.
- Mohrman, D. E., & Heller, L. J. (2014). Cardiovascular Physiology. 8th ed. New York: McGraw-Hill Education.
- Rhoades, R. A., & Tanner, G. A. (2012). Medical Physiology. 2nd ed. Philadelphia: Lippincott Williams & Wilkins.