1. The Heart: Conduction System
Intrinsic conduction system (nodal system)
Function = coordinates the action of the heart chambers and causes the heart to beat faster than it would otherwise
Heart muscle cells contract, without nerve impulses, in a regular, continuous way
The heart has an intrinsic ability to contract that is different from all other muscles in the body. Whereas the nervous system my increase of decrease its rate, the heart continues to beat even if all nervous connections are cut.

2. Elements of the Intrinsic Conduction System
Special tissue sets the pace
1. Sinoatrial node = SA node (“pacemaker”),
is in the right atrium
2. Atrioventricular node = AV node,
is at the junction of the atria and ventricles
3. Atrioventricular bundle = AV bundle (bundle of His),
is in the interventricular septum
4. Bundle branches
are in the interventricular septum
5. Purkinje fibers
spread within the ventricle wall muscles

3. Heart Contractions Sinoatrial Node (SA node)- starts the contraction
Sequential stimulation
Force cardiac muscle depolarization in one direction—from atria to ventricles

4. Heart Contractions Once SA node starts the heartbeat At the AV node,
Impulse spreads to the AV node Then the atria contract
At the AV node,
Impulse passes through the AV bundle, bundle branches, and Purkinje fibers “wringing” contraction of ventricles
Result =Blood is ejected from the ventricles to the aorta and pulmonary trunk

5. Heart Contractions
Figure 11.6

6. Heart Contractions
Tachycardia—rapid heart rate over 100 beats per minute
Bradycardia—slow heart rate less than 60 beats per minutes

7. The Heart: Cardiac Cycle
Cardiac cycle= events of one complete heartbeat, during which both atria and ventricles contract and then relax
Atria contract simultaneously
Atria relax, then ventricles contract
Since most of the pumping is done by ventricles the following terms refer to the ventricles
Systole = contraction
Diastole = relaxation

8. Filling Heart Chambers: Cardiac Cycle
DUB
LUB
Atrial contraction
Mid-to-late diastole (ventricular filling)
Ventricular systole (atria in diastole)
Early diastole
Isovolumetric contraction phase
Ventricular ejection phase
Isovolumetric relaxation
Ventricular filling
Left atrium
Right atrium
Left ventricle
Right ventricle
LUB DUB is caused by the closing of the heart valves
Figure 11.7

9. Filling Heart Chambers: Cardiac Cycle
Mid-to-late diastole (ventricular filling)
Ventricular filling
Left atrium
Right atrium
Left ventricle
Right ventricle
Atria relaxed!
Ventricles relaxed!
AV valves open!
Semilunar valves closed!
Figure 11.7, step 1a

10. Filling Heart Chambers: Cardiac Cycle
Atrial contraction
Mid-to-late diastole (ventricular filling)
Ventricular filling
Left atrium
Right atrium
Left ventricle
Right ventricle
Atria contract!
Ventricles relaxed!
AV valves open!
Semilunar valves closed!
Figure 11.7, step 1b

11. Filling Heart Chambers: Cardiac Cycle
Atrial contraction
Mid-to-late diastole (ventricular filling)
Ventricular systole (atria in diastole)
Isovolumetric contraction phase
Ventricular filling
Left atrium
Right atrium
Left ventricle
Right ventricle
Close AV valves!
AV valves closed! “LUB”
Semilunar valves closed!
Figure 11.7, step 2a

12. Filling Heart Chambers: Cardiac Cycle
Ventricles contract!
Atrial contraction
Mid-to-late diastole (ventricular filling)
Ventricular systole (atria in diastole)
Isovolumetric contraction phase
Ventricular ejection phase
Ventricular filling
Left atrium
Right atrium
Left ventricle
Right ventricle
AV valves closed!
Semilunar valves open!
Figure 11.7, step 2b

13. Filling Heart Chambers: Cardiac Cycle
Ventricles relax!
Atrial contraction
Mid-to-late diastole (ventricular filling)
Ventricular systole (atria in diastole)
Early diastole
Isovolumetric contraction phase
Ventricular ejection phase
Isovolumetric relaxation
Ventricular filling
Left atrium
Right atrium
Left ventricle
Right ventricle
AV valves closed!
Semilunar valves closed!
“DUB”
Figure 11.7, step 3

14. The Heart: Cardiac Cycle
Cardiac cycle—events of one complete heart beat
Mid-to-late diastole—blood flows from atria into ventricles
Ventricular systole—blood pressure builds before ventricle contracts, pushing out blood
Early diastole—atria finish refilling, ventricular pressure is low

15. Abnormal Heart Sounds Murmurs = inicate valve problems
Blood flows silently as long as the flow is smooth and uninterrupted. If it strikes obstructions, its flow becomes turbulent and generates sounds.
If a valve does not close tightly, a swishing sound will be heard as the blood flows back through the partially open valve.
If valves are narrowed, distinct sounds will also be heard.

16. The Heart: Cardiac Output
Cardiac output (CO)
Amount of blood pumped by each side (ventricle) of the heart in one minute
Stroke volume (SV)
Volume of blood pumped by each ventricle in one contraction (each heartbeat)
Usually remains relatively constant
About 70 mL of blood is pumped out of the left ventricle with each heartbeat
Heart rate (HR)
Typically 75 beats per minute

17. The Heart: Cardiac Output
CO = HR  SV
CO = HR (75 beats/min)  SV (70 mL/beat)
CO = 5250 mL/min
Starling’s law of the heart—the more the cardiac muscle is stretched, the stronger the contraction
Changing heart rate is the most common way to change cardiac output

18. The Heart: Regulation of Heart Rate
Increased heart rate
Sympathetic nervous system
Crisis
Low blood pressure
Hormones
Epinephrine
Thyroxine
Exercise
Decreased blood volume

19. Increased heart rate Crisis stressors Low blood pressure Hormones
Exercise
Decreased blood volume

20. The Heart: Regulation of Heart Rate
Decreased heart rate
Parasympathetic nervous system
High blood pressure or blood volume
Decreased venous return

21. Cardiac Output Regulation
Figure 11.8