Key Questions about the Physiology of the Heart

1. How often does the heart re- circulate the body’s blood?  The heart re-circulates the body’s supply of blood over 1000 times per day

2. Describe the intrinsic conduction system:  This tissue is like a cross between muscle and nervous tissue. It causes heart muscle depolarization in one direction—from the atria to the ventricles.  It enforces a steady contraction rate of approximately 75 beats per minute on cardiac muscle

3. What is the sinoatrial (SA) node?  The SA node is a crescent-shaped node of tissue located in the right atrium. It’s function is to start each heart beat and set the pace for the heart

4. Trace the path of a depolarization impulse:  From the SA node, it spreads through the atria to the AV node, causing the atria to contract  At the AV node, the impulse pauses to allow the atria to contract, then it passes rapidly through the AV bundle, resulting in a “wringing” motion of the ventricles

5. What is fibrillation, and what causes it?  Fibrillation is a rapid, uncoordinated shuddering of heart muscle caused by ischemia, which is a lack of adequate blood supply to the heart muscle

6. Contrast tachycardia and bradycardia:  Tachycardia is a rapid heart beat (over 100 beats per minute)  Bradycardia is a slow heart beat (less than 60 beats per minute)

7. What are systole and diastole?  Systole is contraction of atria or ventricles  Diastole is relaxation of the ventricles

8. What causes the “lub” and “dup” sounds of the heart beat?  The “lub” is caused by the closing of the AV valves  The “dup” is the closing of the semilunar valves at the end of systole

9. What are murmurs? What do they indicate?  Abnormal or unusual heart sounds are murmurs, caused when blood strikes obstructions in its flow.  Murmurs indicate problems with the valves of the heart

10. What is cardiac output, and what is the average for an adult?  Cardiac output is the amount of blood pumped out by each ventricle in 1 minute. It is the product of heart rate and stroke volume.  The average adult cardiac output is 5250 ml per minute

11. What is Starling’s Law of the Heart?  The critical factor controlling stroke volume is how much the cardiac muscle cells are stretched just before they contract

12. When does the sympathetic division stimulate the heart to beat faster?  During times of physical or emotional stress, such as being frightened or running to catch a bus, the sympathetic division stimulates the heart to beat faster

13. How does heart rate change?  Resting heart rate is fastest in the fetus, then gradually decreases throughout life  The average heart rate is about 8 beats per minute higher in women than men

14. What is congestive heart failure?  Congestive heart failure occurs when the pumping efficiency of the heart is depressed so that circulation is inadequate to meet tissue needs.  It reflects weakening of the heart by coronary artherosclerosis

15. Describe the effects of pulmonary congestion and peripheral congestion:  Pulmonary: if the left side of the heart fails, the right side continues to pump blood to the lungs. Blood vessels in the lungs back up and become swollen with blood, causing suffocation  Peripheral: blood backs up in the systemic circulation, specifically the distal parts of the body (feet, ankles, or fingers)