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The Cardiac Cycle

The Cardiac Cycle

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The Cardiac Cycle

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  1. The Cardiac Cycle

  2. Cardiac Cycle • The cardiac cycle is one complete heart beat – a contraction and relaxation of each heart chamber; 1 cycle = 0.8s • 2 basic phases: • Diastole: ventricles relax to fill with blood • Systole: Ventricles contract to push blood into arteries

  3. Summary of Events in Cardiac Cycle 1) Atria are relaxed and fill with blood 2) Atria contract and force blood into the ventricles through the AV valves 3) Ventricles contract forcing AV valves shut and SL valves open; blood moves into arteries 4) Ventricles relax, causing SL valves to snap shut

  4. Heart Sounds • Lubb-DUBB sound is caused by closing of AV and SL valves • “Lubb” caused by closing of AV valves; double sound because left valve closes slightly before right • “DUBB” caused by closing of SL valves • When valves do not close properly, can hear sound of blood leaking through when valves shut = heart murmur

  5. Activity: Listening to Heart Sounds • Using a stethoscope, listen to the lubb-DUBB sound of your heart • Where do you notice the clearest sound? • Compare sitting vs. standing • Compare normal and abnormal heart sounds • http://depts.washington.edu/physdx/heart/demo.html

  6. Heart Rhythm • Heart beats on it’s own, without input from the brain • A cluster of nerve cells in the right atrium, called the sinoatrial (SA) node, generate electrical impulses and set the rhythm for the heart • SA node causes atria to contract, and stimulates AV node • AV node and Purkinje fibers cause ventricles to contract

  7. Observing Heartbeats: Electrocardiographs • An electrocardiograph is a machine that detects electrical signals from the heart and records them as an electrocardiogram. P wave: atrial contraction QRS complex: ventricular contraction T wave: recovery from contraction

  8. Heart Abnormalities • Murmurs – improper valve closing • Stenosis – narrowing of blood vessel (pulmonary or aortic), causes enlargement of one ventricle • Septal defects – hole between atria or hole between ventricles (allows oxy and deoxy blood to mix)