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بسم هللا الرحمن الرحيم ﴿و ما أوتيتم من العلم إال قليال﴾ صدق هللا العظيم االسراء اية 58 Dra abdelaziz Hussein, Mansoura Faculty of Medicine By Dr. Abdel Aziz M. Hussein Lecturer of Medical Physiology Member of American Society of Physiology Dra abdelaziz Hussein, Mansoura Faculty of Medicine Dra abdelaziz Hussein, Mansoura Faculty of Medicine • 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 a)Coronary arteries: •2 coronary arteries arise from aorta just above the aortic valve Dra abdelaziz Hussein, Mansoura Faculty of Medicine Lt coronary artery Rt coronary artery -Lt atrium -Lt ventricle -Anterior part of interventricular septum -Rt atrium -Rt ventricle -Posterior part of interventricular septum Dra abdelaziz Hussein, Mansoura Faculty of Medicine Dra abdelaziz Hussein, Mansoura Faculty of Medicine a)Coronary arteries: • 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 Dra abdelaziz Hussein, Mansoura Faculty of Medicine 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 • 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 • 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 ◊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 Arterial O2 content Venous O2 content O2 consumption O2% extraction Venous O2 reserve Coronary vessels (ml %) Other tissue vessels (ml %) 19 19 5 14 14 5 70% 25% Low High Dra abdelaziz Hussein, Mansoura Faculty of Medicine • 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 ◊ 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 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 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 Dra abdelaziz Hussein, Mansoura Faculty of Medicine Dra abdelaziz Hussein, Mansoura Faculty of Medicine • 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 Intrinsic mechanisms (autoregulation) Extrinsic mechanisms 1. Nervous regulation O2 demand or need 2. Chemical regulation 3. Mechanical regulation Dra abdelaziz Hussein, Mansoura Faculty of Medicine • 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 Dra abdelaziz Hussein, Mansoura Faculty of Medicine and prostaglandin. as adenosine K, H, CO2, bradykinin Dra abdelaziz Hussein, Mansoura Faculty of Medicine 1. Active hyperaemia occurs in the heart during exercise. 2. 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 Dra abdelaziz Hussein, Mansoura Faculty of Medicine 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 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 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 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 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 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 1. Nitroglycerin sublingually has a fast coronary dilating effect, within 2-3 minutes. 2. Long acting nitrates as 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 Dra abdelaziz Hussein, Mansoura Faculty of Medicine • All these chemicals are important in treatment of coronary artery diseases. Dra abdelaziz Hussein, Mansoura Faculty of Medicine 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 Hussein, myocardial blood flow. Dra abdelaziz Mansoura Faculty of Medicine Dra abdelaziz Hussein, Mansoura Faculty of Medicine THANKS Dra abdelaziz Hussein, Mansoura Faculty of Medicine