(1). heart rate ↑→cardiac output

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Wu Minfan Department of Physiology, Shenyang Medical College

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Introduction(F) The cardiovascular system consists of the heart and the blood vessels. The right ventricle pumps blood through the pulmonary circulation to the left atrium. The left ventricle ejects blood through the systemic circulation to the right atrium. The function of blood circulation is to transport substances in human body.

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Systemic and Pulmonary Circulation

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b. pumps blood to pulmonary circulation, and then to left heart. 2. Left Heart a. receives oxygenated blood from pulmonary circulation via pulmonary vein into left atrium. b. pumps blood into systemic circulation, and then to right heart.1. Right Heart a. receives venous blood from systemic circulation via superior and inferior vena cava into right atrium.

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Heart Valves1. Atrioventricular V a. mitral--between LA and LV; two leaflets b. tricuspid--between RA and RV; three leaflets2. Semilunar V a. aortic--three leaflets b. pulmonary--three leaflets

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Prevent backward flow Provide low resistance to forward flowFunction of Heart Valves

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Section one Pump function of the heartThe busy and hard working heart!

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1.Concept: The period of one contraction and one relaxation of the heart. 2.Relationship of the cardiac cycle and Heart rateI. Cardiac CycleHeart rate:75 beats/min 60s Cardiac cycle = —— =0.8sec 75

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A cardiac cycle consists of a systole and a diastole. Atrial cycle equals to ventricular cycle. Diastole is longer than systole. When heartbeat becomes more rapid, the cardiac cycle is shorter, and the diastole is much shorter than normal. Tachycardia is unfavourable for the heart.

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AtriumVentricle 0.1s 0.7s0.3s 0.5sContraction RelaxationWhole heart relaxation phase means this period of the first 0.4s of the ventricular relaxation in which atrium is also in relaxation state.

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1. For example: Processess of blood ejection and filling in the left ventricle(1)Period of isovolumic contraction 0.05s (2)Period of rapid ejection 0.1s (3)Period of slow ejection 0.15sII. Mechanical events of the cardiac cycleVentricular Systole

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(4)period of isovolumic relaxation 0.07s (5)Period of rapid filling 0.11s (6)Period of slow filling 0.22s (7)Atrial systole 0.1sVentricular Diastole

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2. The Phases of the Cardiac Cycle Period of isovolumic contractionEvents: ventricular contraction ventricular pressure rise  atrioventricular valve close  the ventricular pressure increase sharply Period: 0.05 sec atrioventricular valve close  S1- first heart sound Importance: enable the ventricular pressure to rise from 0 to the level of aortic pressure

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(2) Period of ejection Events: ventricular contraction continuously the ventricular pressure rise above the arterial pressure semilunar valves open  blood pours out of the ventricles

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Rapid ejection period (0.10s, 66% of the total ejected blood volume, stroke volume) Reduced ejection period (0.15s, 34% of the total ejected blood volume , stroke volume) The aortic pressure actually exceeds the ventricular pressure, but momentum keeps the blood moving forward.

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(3) Period of isovolumic relaxationEvents: ventricular muscle relax the ventricular pressure fall lower than the aortic pressure aortic valve close the ventricular pressure fall sharply

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S2- second heart sound ←closure of aortic and pulmonary semilunar valves at beginning of ventricular diastole Period: 0.06-0.08 s Importance: Enable the ventricular pressure to fall to the level near the atrial pressure

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(4) Period of filling of the ventricles Events: Ventricular muscle relax continuously  the ventricular pressure is equal or lower than the atrial pressure  atrioventricular valve open blood accumulated in the atria rushes into the ventricle blood flow quickly from the atrium to the ventricle.

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Period of rapid filling. (0.11s, amount of filling, 2/3 of total filling blood volume) 2) Period of reduced filling (0.22s, little blood fills into the ventricle)

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(5) Atrial systole Significance, 25% of total filling blood volume During high output states or in the failing heart, the amount added by atrial contraction may be of major importance in determining the final cardiac output.

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Correlation of events in the left side of the heart in each cardiac cycleAtrial SystoleMitral ClosesIsovolumic contract.Aortic opensS1Rapid EjectionReduced EjectionIsovolumic Relax.Aortic closesRapid Ventricular FillingMitral opensS2Reduced Ventricular FillingAtrial Systole:>O:>D

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Heart sounds Action of the heart produces mechanical vibrations which are audible at the chest wall as the heart sounds. The first heart sound is caused by closure of the atrioventricular valves and so marks the beginning of ventricular systole. The second heart sound is caused by closure of the aortic and pulmonary valves and so marks the beginning of ventricular diastole.

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The third heart sound is caused by sudden stretch of the ventricular wall and papillary muscle, and sudden deceleration of filling flow at the end of rapid filling period. The fourth heart sound is caused by unusually strong atrial contraction at the end of ventricular diastole.

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III. Cardiac Output1.Stroke volume The amount of blood pumped out of each ventricle per beat is called the stroke volume, about 70mL in a resting adult.Stroke volume = end diastolic volume – end systolic volume

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2.Ejection fraction stroke volume70×100% 125 —— =56%End diastolic volume × 100% = ejection fractionthe normal range is: 55-65%

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3.Cardiac output The output of each ventricle per minute is called the cardiac output. Cardiac Output = Stroke Volume× Heart Rate CO=SV×HR =70 × 75 =5250(ml)It varies with sex, age, and exercise

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Last Updated: 8th March 2018

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