医学英语心脏PPT课件.ppt

How does the Heart work? STEP ONE blood from the body blood from the lungs The heart beat begins when the heart muscles relax and blood flows into the atria. How does the Heart work? STEP TWO The atria then contract and the valves open to allow blood into the ventricles. How does the Heart work? STEP THREE The valves close to stop blood flowing backwards. The ventricles contract forcing the blood to leave the heart. At the same time, the atria are relaxing and once again filling with blood. The cycle then repeats itself. Filling of Heart Chambers – the Cardiac Cycle Copyright ? 2003 Pearson Education, Inc. publishing as Benjamin Cummings The Heart: Cardiac Output ? Cardiac output (CO) total vent blood/min ? Amount of blood pumped by each side of the heart in one minute ? CO = (heart rate [HR]) x (stroke volume [SV]) ? Stroke volume ? Volume of blood pumped by each ventricle in one contraction Copyright ? 2003 Pearson Education, Inc. publishing as Benjamin Cummings S1- What is it ? closing of the bicuspid and tricuspid valves. (closure of the AV valves) The Pulmonic and Aortic valves are opening and blood is being forced into the arteries S2- The sounds are because of What is it ? the closing of the Pulmonic (closure of the semilunar and Aortic valves valves) Conductive System The SA node , or pacemaker , initiates the heartbeat and causes the atria to contract on average every 0.85 seconds. The AV node conveys the stimulus and initiates contraction of the ventricles. The signal for the ventricles to contract travels from the AV node through the atrioventricular bundle to the smaller Purkinje fibers . Action potential- electrical impulse causing the contraction of heart muscle cells Electrocardiogram ? An electrocardiogram (ECG) is a recording of the electrical changes that occur in the myocardium during a cardiac cycle. ? The P wave occurs just prior to atrial contraction; the QRS complex occurs just prior to ventricu