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بسم الله الرحمن الرحيم

بسم الله الرحمن الرحيم. ﴿و ما أوتيتم من العلم إلا قليلا﴾. صدق الله العظيم الاسراء اية 58. Coronary Circulation. By Dr. Abdel Aziz M. Hussein Lecturer of Medical Physiology Member of American Society of Physiology. Coronary Circulation. Coronary Circulation.

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بسم الله الرحمن الرحيم

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  1. بسم الله الرحمن الرحيم ﴿و ما أوتيتم من العلم إلا قليلا﴾ صدق الله العظيم الاسراء اية 58 Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  2. Coronary Circulation By Dr. Abdel Aziz M. Hussein Lecturer of Medical Physiology Member of American Society of Physiology Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  3. Coronary Circulation Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  4. Coronary Circulation • The coronary circulation concerned with the blood supplying the cardiac ms. • About 1/3 of people die from diseases of coronary arteries. Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  5. Coronary Vessels a)Coronary arteries: • 2 coronary arteriesarise from aorta just above the aortic valve Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  6. Coronary Vessels Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  7. Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  8. Coronary Vessels • There are small anastomotic connections ( ) the 2 coronaries, but they are not sufficient to supply the cardiac ms with blood, if one of them is occluded→ functional end arteries a)Coronary arteries: Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  9. Coronary Vessels b) Coronary capillaries: They run parallel to the cardiac ms fibers. There is about one coronary capillary for each ms fiber. Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  10. Coronary Vessels • c) Coronary venous drainage: • There are 2 venous systems; • i) Superficial system: • It includes coronary sinus and the anterior cardiac vein • They drain mainly left ventricle • They open into Rt atrium Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  11. Coronary Vessels • c) Coronary venous drainage: • i) Superficial system: • The coronary sinus drains about 60% of total coronary venous blood. • ii) Deep system: • It includes thebesian veins which drain small amount of the coronary venous blood directly into all chambers of the heart. Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  12. O2 consumption of heart ◊Value: • At rest→ it is about 70% of O2 in the coronary arterial blood. • On other tissues → it is about 25% of O2. Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  13. Characters of O2 consumption in coronaries and other systemic tissues Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  14. O2 consumption of heart • The coronary venous blood has low venous O2 reserve. • -In severe exercise, the O2 consumption is ↑ed by; • a) ↑ed coronary blood flow. • b) Marked ↓ in venous O2 reserve. • c) ↑ O2 delivered from myoglobin. Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  15. Coronary Blood Flow ◊ Value: • -During rest: • It is about 250 ml/minute (about 5% of the COP). • -In severe exercise: It ↑es to 3-4 fold. Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  16. Coronary Blood Flow Measurement: The CBF is measured by Kety method → depends on the application of direct Fick's principle. The person breathes subanaesthetic dose of N2O mixed with oxygen for 10 minutes. N2O uptake by the heart/min. Coronary blood flow = ——————————————— Arterio - Venous coronary N2O difference Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  17. Phasic Changes in CBF 1) During systole: • The CBF in the Lt ventricle falls to a low value → due to strong compression of the left ventricular ms around the intramuscular vessels during systole. • The lowest CBF occurs during the isometric contraction phase (the flow may stop completely) • Such ↓ in CBF during systole is compensated for by O2 delivered from myoglobin. • Myoglobin is loaded with O2 during diastole Draabdelaziz Hussein, Mansoura Faculty of Medicine

  18. Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  19. Phasic Changes in CBF • 2) During diastole: • The cardiac ms relax completely and so, the blood flows rapidly into the coronary arteries. • The highest CBF occurs during isometric relaxation phase N.B. • Phasic changes in the Rt ventricle is relatively less than that of the Lt ventricle because the force of contraction of the Rt ventricle is far less than that of the Lt ventricle Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  20. Regulation of CBF Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  21. Autoregulation of CBF • It is the main mechanism controlling CBF. • ◊Mechanism: • It is regulated almost entirely by local need of cardiac ms for nutrition. • O2 demand is the major factor in local blood flow regulation. • O2 lack (due to ↑ heart activity) is followed by coronary VD due to: • 1) ↓ed O2 tension→ in the coronary blood has a direct relaxing effect on the smooth ms in the wall of the coronary arteries. • 2) O2 lack→ release of VD substances by the tissues, such as adenosine K, H, CO2, bradykinin and prostaglandin. Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  22. Autoregulation of CBF Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  23. Autoregulation of CBF Active hyperaemia occurs in the heart during exercise. Reactive hyperaemia occurs if the coronaries are temporarily occluded leading to increase of the CBF about 3-4 folds Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  24. Active and reactive Hyperemia Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  25. Nervous Factors • a) Sympathetic ++: • Direct action → VC due to ++ of α1 receptors and mild VD due to ++ of β2 receptors. • Indirect action → it ↑es the metabolic activity of the heart → strong VD. • The net effect of sympathetic ++ is an ↑ in the coronary blood flow. • b. Parasympathetic++→ has an opposite effect to sympathetic ++ on the coronary arteries. Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  26. Nervous Factors • c. Anrep's reflex: • ↑ VR and venous pressure in the Rt atrium → reflex coronary VD and ↑es the coronary B.F. • Significance: • It is important in exercise to supply the cardiac ms with more O2. Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  27. Nervous Factors • d. Gastrocoronary reflex: • Distension of the stomach with heavy meal produces reflex coronary VC and ↓CBF → anginal pain may be felt in certain persons after heavy meals. Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  28. Mechanical Factors • a) Phases of cardiac cycle: • b) Heart rate: • ↑HR → ↓es the coronary blood flow by shortening of the diastolic period. • ↓ HR → ↑es the coronary blood flow by prolonging the diastole. • c) Mechanical occlusion of coronary artery: • Reactive hyperaemia occurs Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  29. Mechanical Factors • d) ABP: • ↑ed ABP→ ↑es coronary flow • This is antagonized by ↑ed vagal tone • ↑ed vagal tone produces coronary VC and ↓CBF → so the net ↑ in coronary flow is slight. • • Conversely, diastolic BP e.g aortic regurge  CBF. Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  30. Mechanical Factors • e) Cardiac output: • Increase COP  increase coronary BF. • Helped by: • Increase COP  decrease vagal tone  VD of coronary arteries  increase coronary BF. • Net effect: great increase in coronary BF Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  31. Chemical Factors 1. Nitroglycerinsublingually has a fast coronary dilating effect, within 2-3 minutes. 2. Long acting nitratesas iso-sorbide dinitrate given orally also produce coronary dilatation. 3. Beta-blockers, e.g. propranolol and atenolol act by reducing myocardial O2 requirements during exertion and stress. 4. Calcium entry blocking agents, e.g. nifedipine and verapamil also reduce myocardial O2 requirements and induce coronary VD. Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  32. Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  33. All these chemicals are important in treatment of coronary artery diseases. Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  34. Summary of Characteristics of coronary circulation 1. It is very short and rapid circulation. 2. The arterio-venous O2 difference is high, due to high O2 extraction by the cardiac ms. 3. Very low venous O2 reserve. 4. It is the only circulation where blood flow occurs mainly during diastole. 5. The coronary arteries are terminal arteries having little anastomosis. 6. The coronary arteries are common sites for atherosclerosis causing their narrowing or occlusion. 7. The metabolic factors especially myocardial O2 need are the major controllers of myocardial blood flow. Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  35. Angina pectoris and Myocardial Infarction Dra abdelaziz Hussein, Mansoura Faculty of Medicine

  36. THANKS Dra abdelaziz Hussein, Mansoura Faculty of Medicine

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