1. The Cardiac Cycle

2. Cardiac Cycle aka “heartbeat” aka “heartbeat” each heartbeat (cycle) blood is forced out of ventricles each heartbeat (cycle) blood is forced out of ventricles –right – lungs –left – body –Average resting heart beats 70-75 times per minute, so each heart beat takes less than 1 second. stroke volume – volume of blood pumped by a ventricle per heartbeat stroke volume – volume of blood pumped by a ventricle per heartbeat –average adult pumps about 5 L/min cardiac output – volume of blood the heart pumps per minute cardiac output – volume of blood the heart pumps per minute = the product of (multiply) stroke volume (SV) by heart rate (HR) ( in beats/min) = SV x HR

3. Cardiac cycle and Valves In 1 cardiac cycle: In 1 cardiac cycle: the blood goes first from atria to ventricles the blood goes first from atria to ventricles –the atriaventricular (AV) valves are open –Atriaventricular valves = valves between the atria and ventricles (tricuspid and bicuspid) 2 nd the blood goes from ventricles to blood vessels (aorta and pulmonary artery) 2 nd the blood goes from ventricles to blood vessels (aorta and pulmonary artery) –the semilunar valves are open –Semilunar valves = valves between the ventricles and blood vessels (aortic and pulmonary)

4. Steps of Cardiac Cycle systole – contraction of heart muscle systole – contraction of heart muscle diastole – relaxation of heart muscle diastole – relaxation of heart muscle 1 cardiac cycle consists of systole and diastole 1 cardiac cycle consists of systole and diastole steps steps 1.atria contract (systole) forcing blood into relaxed ventricles 1.AV valves are open, semilunar valves are closed 2.ventricles contract (systole) forcing blood into pulmonary trunk and aorta; atria relax –AV valves closed; semilunar valves open 3.both atria and ventricles relax (diastole) and fill with blood passively

6. Heart Sounds created by vibrations caused by pressure changes in chambers and valves closing created by vibrations caused by pressure changes in chambers and valves closing “lub” –AV valves close and ventricles contract “lub” –AV valves close and ventricles contract “dub” – semilunar valves close and ventricles relax “dub” – semilunar valves close and ventricles relax

7. Regulation of Cardiac Cycle rate controlled by cardiac control center in the medulla oblongata in the brain stem rate controlled by cardiac control center in the medulla oblongata in the brain stem influenced by cerebrum and hypothalamus influenced by cerebrum and hypothalamus –anxiety/stress, activity speed up rate –meditation, yoga, sleep slow down rate other influences: other influences: –temperature, electrolyte balance (K + and Ca 2+ ), blood pressure

8. Pulse pulse = the pressure wave in the arteries as they expand with the contraction of the ventricles. pulse = the pressure wave in the arteries as they expand with the contraction of the ventricles.

9. Blood Pressure blood pressure (BP) – force of blood against blood vessel walls blood pressure (BP) – force of blood against blood vessel walls BP moves blood through arteries, arterioles and capillaries, but skeletal muscle contraction moves blood through venules and veins BP moves blood through arteries, arterioles and capillaries, but skeletal muscle contraction moves blood through venules and veins factors that influence BP factors that influence BP –cardiac output – heartrate and blood volume –peripheral resistance – arterial constriction –hormones – epinephrine, norepinephrin, ADH

10. Measuring BP sphygomomanometer sphygomomanometer measured in brachial artery in mm Hg measured in brachial artery in mm Hg –normal BP = 120/80 mm Hg –systolic/diastolic systolic pressure is recorded in an artery when L ventricle contracts systolic pressure is recorded in an artery when L ventricle contracts diastolic pressure is recorded in an artery when L ventricle relaxes diastolic pressure is recorded in an artery when L ventricle relaxes hypertension – high BP hypertension – high BP

11. Review Questions 1. What is a heartbeat? What is the average resting heart beat rate? 2. Define cardiac output. 3. What are the atriaventricular valves and what are their names? What are the semilunar valves and what are their names? 4. What are the 3 basic steps of the cardiac cycle? 5. What is systole and what is diastole? 6. Rewrite the 3 basic steps of the cardiac cycle using systole and diastole instead of contract and relax. 7. What creates the heart sounds?

12. Review Questions 8.What is pulse? 9.What is blood pressure? 10.What is the average blood pressure? 11.How is blood pressure measured? 12.What are the two parts of blood pressure?

13. Cardiac Conduction System coordinates the events of the cardiac cycle coordinates the events of the cardiac cycle sinoatrial node (SA node) – pacemaker sinoatrial node (SA node) – pacemaker –located in R atrium near superior vena cava –initiates impulses that cause cardiac muscle cells to contract w/o stimulation from nerve fibers –rhythmic: 70 – 80 times per minute –atria contract

14. Cardiac Conduction System atrioventricular node (AV node) – initiates ventricular contraction atrioventricular node (AV node) – initiates ventricular contraction AV bundle – branches into L and R AV bundle – branches into L and R Purkinje fibers – Purkinje fibers – –wrap around tip and travel up lateral walls of ventricles –highly branched –contract ventricles with twisting motion

16. Electrocardiogram (ECG) aka electrokardiogram (EKG) aka electrokardiogram (EKG) recording of the electrical changes in the myocardium during a cardiac cycle recording of the electrical changes in the myocardium during a cardiac cycle P wave – depolarization of atria P wave – depolarization of atria QRS complex – depolarization of ventricles QRS complex – depolarization of ventricles –thicker walls require greater electrical change –repolarization of atria obscured T wave – repolarization of ventricles T wave – repolarization of ventricles tachycardia – fast heartbeat tachycardia – fast heartbeat bradycardia – slow heartbeat bradycardia – slow heartbeat

17. ECGs

18. Review Questions 1. How is the cardiac impulse initiated? 2. How is a cardiac impulse transmitted from the right atrium to the other heart chambers? 3. What is an electrocardiogram? 4. Which cardiac events do the P wave, QRS complex, and T wave represent?