1. Heart Physiology
Chapter 11

2. Microscopic Anatomy Cardiac muscle fibers (cells)
Striated, short, and branched
One nucleus
Plasma membrane of adjacent cardiac cells interlock at intercalated discs
Large mitochondria account for 25% of the volume and give the cells high resistance to fatigue
Only operates on aerobic respiration
Contracts by the sliding filament mechanism
Self-excitable and can initiate their own depolarization
Spontaneous and rhythmic stimulation
The heart contracts as a unit or not at all because all cells are tied together at intercalated discs

3. Physiology of The Heart
Cardiac muscle cells have the ability to contract intrinsically (within) or with autonomic NS
Contractions occur in a regular continuous rhythm
Heart needs a control system to be an efficient pump
Main conduction system is the intrinsic conduction system
Specialized non-contractile cardiac cells that initiate and distribute impulses throughout the heart so that it contracts

4. Intrinsic Conduction System
Sinoatrial node (SA)
Located in the right atrial wall
Pacemaker (sets the pace for HR)
Atrioventricular (AV) node
Located between atria and ventricles
Atrioventricular bundle (Bundle of His)
Located in the septum
Right and left bundle branches
Purkinje fibers
Spread in the ventricle walls

5. Intrinsic Conduction System
Sinoatrial (SA) node starts each heartbeat and sets the pace – pacemaker
Impulse spreads through the atria to the AV node (causing the atria to contract)
Impulse pauses for a 0.1 sec to allow atria to finish contracting
Then the impulse goes through the AV bundle (bundle of His) and splits into the right and left bundle branches
The impulse ends in the Purkinje fibers causing the ventricles to contract

6. Nervous System Conduction System
Basic heart rate is set by intrinsic conduction system
Autonomic nervous system can modify the heart rate
Sympathetic activation increases the heartbeat
Parasympathetic activation slows the heartbeat

7. Conduction System Imbalances
Arrhythmias
Irregular heart rhythms due to defects in the intrinsic conduction system
Fibrillation
A condition of rapid and irregular contractions
Defibrillation is accomplished by electrically shocking the heart which interrupts the chaotic twitching
Heart block
Damage to the AV node, totally or partially releasing the ventricles from the control of the sinoatrial (SA) node

8. Electrocardiography (ECG or EKG)
Electrical currents generated and transmitted through the heart spread throughout the body and can be detected with an electrocardiograph
A graphic record of heart activity is called an electrocardiogram (ECG or EKG)
Recording electrodes are positioned at various sites on the body surface
12 leads are typically used

9. Electrocardiography (ECG or EKG)
Typical ECG has 3 waves
P wave
Atrial depolarization before they contract
QRS complex
Depolarization of ventricles and contraction of ventricles
T wave
Ventricle repolarization

10. Electrocardiography (ECG or EKG)
P-R interval
From the atrial excitation to the beginning of ventricular excitement
S-T segment
Action potentials of the ventricular cells are in their plateau phases
Q-T interval
From the beginning of ventricular depolarization through ventricular repolarization

11. Electrocardiography (ECG or EKG)
In a healthy heart the size, duration and timing of the waves tend to be consistent
Changes in the pattern or timing may reveal a diseased or damaged heart or problems with the heart’s conduction system
Example: an enlarged R wave hints of enlarged ventricles

12. Electrocardiography (ECG or EKG)

13. Heart Sounds http://www.viddler.com/explore/humananatomy/videos/7/
Two sounds (lub-dup) can be heard when listening to the thorax with a stethoscope
Associated with the closing of the valves
First sound (lub) occurs when the AV valves close
Second sound (dup) occurs when the SL valves close

14. Heart Sounds Heart murmurs Abnormal heart sounds
Blood flows silently as long as the flow is smooth
If it strikes obstructions, its flow generates heart murmurs that can be heard with a stethoscope

15. The Cardiac Cycle Cardiac cycle Diastole Systole
All events associated with the blood flow through the heart during one complete heartbeat
Diastole
Relaxation period (atria and ventricles)
Systole
Contraction period (atria and ventricles)

16. The Cardiac Cycle
Ventricular filling: mid-to-late diastole (AV valves open)
Ventricular systole (SL valves open)
Early diastole (AV valves open)

17. Heart Rate
Heart rate can be affected by age, gender, exercise and body temperature
Resting heart rate is fastest in the fetus
beats/min
Average heart rate for females
72-80 beats/min
Average heart rate for males
64-72 beats/min

18. Heart Rate Tachycardia Bradycardia
Abnormally fast heart rate more than 100 beats/min
Results from elevated body temperature, stress, certain drugs, or heart disease
Bradycardia
Heart rate slower than 60 beats/min
Results from low body temperature, certain drugs or parasympathetic activation

19. The Vascular System Arteries Capillaries Veins
Taking blood away from the heart to the tissues
Capillaries
Gas and nutrient exchange
Walls of capillaries are only one cell layer thick to allow for exchanges between blood and tissue
Veins
Taking blood back to (visit) the heart
Skeletal muscle “milks” blood in veins toward the heart

20. Pulse Pressure wave of blood
Monitored at “pressure points” where pulse is easily palpated

21. Blood Pressure
Pressure the blood exerts against the inner blood vessels walls
Because the heart contracts and relaxes, the rhythmic flow of blood causes the pressure to rise and fall each beat.
Systolic – pressure at the peak of ventricular contraction
Diastolic – pressure when ventricles relax

22. Variations in Blood Pressure
Human normal blood pressure range is variable
Pressure in blood vessels decreases as the distance away from the heart increases
Normal
140–110 mm Hg systolic
80–75 mm Hg diastolic
Hypotension
Low systolic (below 110 mm HG)
Often associated with illness
Hypertension
High systolic (above 140 mm HG)
Can be dangerous if it is chronic

23. Measuring Arterial Blood Pressure
Figure 11.18