2. The Cardiac Cycle Heart Murmur
Sounds produced by regurgitation through valves

3. The Cardiac Cycle
Figure 18–18 Heart Sounds

4. Cardiodynamics
The movement and force generated by cardiac contractions
End-diastolic volume (EDV)
End-systolic volume (ESV)
Stroke volume (SV)
SV = EDV – ESV
Ejection fraction
The percentage of EDV represented by SV
Cardiac output (CO)
The volume pumped by left ventricle in 1 minute

5. Cardiodynamics
Figure 18–19 A Simple Model of Stroke Volume

6. Cardiodynamics Cardiac Output CO = HR X SV
CO = cardiac output (mL/min)
HR = heart rate (beats/min)
SV = stroke volume (mL/beat)

7. Cardiodynamics Factors Affecting Cardiac Output Cardiac output
Adjusted by changes in heart rate or stroke volume
Heart rate
Adjusted by autonomic nervous system or hormones
Stroke volume
Adjusted by changing EDV or ESV

8. Cardiodynamics
Figure 18–20 Factors Affecting Cardiac Output

9. Cardiodynamics Factors Affecting the Heart Rate Autonomic innervation
Cardiac plexuses: innervate heart
Vagus nerves (X): carry parasympathetic preganglionic fibers to small ganglia in cardiac plexus
Cardiac centers of medulla oblongata:
cardioacceleratory center controls sympathetic neurons (increases heart rate)
cardioinhibitory center controls parasympathetic neurons (slows heart rate)

10. Cardiodynamics Autonomic Innervation Cardiac reflexes
Cardiac centers monitor:
blood pressure (baroreceptors)
arterial oxygen and carbon dioxide levels (chemoreceptors)
Cardiac centers adjust cardiac activity
Autonomic tone
Dual innervation maintains resting tone by releasing ACh and NE
Fine adjustments meet needs of other systems

11. Cardiodynamics
Figure 18–21 Autonomic Innervation of the Heart

12. Cardiodynamics Effects on the SA Node
Sympathetic and parasympathetic stimulation
Greatest at SA node (heart rate)
Membrane potential of pacemaker cells
Lower than other cardiac cells
Rate of spontaneous depolarization depends on
Resting membrane potential
Rate of depolarization
ACh (parasympathetic stimulation)
Slows the heart
NE (sympathetic stimulation)
Speeds the heart

13. Cardiodynamics
Figure 18–22 Autonomic Regulation of Pacemaker Function

14. Cardiodynamics Atrial Reflex Also called Bainbridge reflex
Adjusts heart rate in response to venous return
Stretch receptors in right atrium
Trigger increase in heart rate
Through increased sympathetic activity

15. Cardiodynamics Hormonal Effects on Heart Rate
Increase heart rate (by sympathetic stimulation of SA node)
Epinephrine (E)
Norepinephrine (NE)
Thyroid hormone

16. Cardiodynamics Factors Affecting the Stroke Volume
The EDV: amount of blood a ventricle contains at the end of diastole
Filling time:
duration of ventricular diastole
Venous return:
rate of blood flow during ventricular diastole

17. Cardiodynamics Preload
The degree of ventricular stretching during ventricular diastole
Directly proportional to EDV
Affects ability of muscle cells to produce tension

18. The Conducting System
Figure 18–13 Impulse Conduction through the Heart

19. The Conducting System
Figure 18–13 Impulse Conduction through the Heart

20. The Conducting System The AV Bundle In the septum
Carries impulse to left and right bundle branches
Which conduct to Purkinje fibers (Step 4)
And to the moderator band
Which conducts to papillary muscles

21. The Conducting System
Figure 18–13 Impulse Conduction through the Heart

22. The Conducting System Purkinje Fibers
Distribute impulse through ventricles (Step 5)
Atrial contraction is completed
Ventricular contraction begins

23. The Conducting System
Figure 18–13 Impulse Conduction through the Heart

24. The Conducting System Abnormal Pacemaker Function
Bradycardia: abnormally slow heart rate
Tachycardia: abnormally fast heart rate
Ectopic pacemaker
Abnormal cells
Generate high rate of action potentials
Bypass conducting system
Disrupt ventricular contractions

25. The Conducting System Electrocardiogram (ECG or EKG)
A recording of electrical events in the heart
Obtained by electrodes at specific body locations
Abnormal patterns diagnose damage

26. The Conducting System Features of an ECG P wave QRS complex T wave
Atria depolarize
QRS complex
Ventricles depolarize
T wave
Ventricles repolarize

27. The Conducting System Time Intervals Between ECG Waves P–R interval
From start of atrial depolarization
To start of QRS complex
Q–T interval
From ventricular depolarization
To ventricular repolarization

28. The Conducting System
Figure 18–14a An Electrocardiogram: Electrode Placement for Recording a Standard ECG

29. The Conducting System
Figure 18–14b An Electrocardiogram: An ECG Printout

30. The Conducting System Contractile Cells
Purkinje fibers distribute the stimulus to the contractile cells, which make up most of the muscle cells in the heart
Resting Potential
Of a ventricular cell: about –90 mV
Of an atrial cell: about –80 mV

31. The Conducting System
Figure 18–15 The Action Potential in Skeletal and Cardiac Muscle

32. The Conducting System
Figure 18–15 The Action Potential in Skeletal and Cardiac Muscle

33. The Conducting System Refractory Period Absolute refractory period
Long
Cardiac muscle cells cannot respond
Relative refractory period
Short
Response depends on degree of stimulus

34. The Conducting System Timing of Refractory Periods
Length of cardiac action potential in ventricular cell
250–300 msecs:
30 times longer than skeletal muscle fiber
long refractory period prevents summation and tetany

35. The Conducting System The Role of Calcium Ions in Cardiac Contractions
Contraction of a cardiac muscle cell is produced by an increase in calcium ion concentration around myofibrils

36. The Conducting System The Role of Calcium Ions in Cardiac Contractions
20% of calcium ions required for a contraction
Calcium ions enter plasma membrane during plateau phase
Arrival of extracellular Ca2+
Triggers release of calcium ion reserves from sarcoplasmic reticulum

37. The Conducting System The Role of Calcium Ions in Cardiac Contractions
As slow calcium channels close
Intracellular Ca2+ is absorbed by the SR
Or pumped out of cell
Cardiac muscle tissue
Very sensitive to extracellular Ca2+ concentrations

38. The Conducting System The Energy for Cardiac Contractions
Aerobic energy of heart
From mitochondrial breakdown of fatty acids and glucose
Oxygen from circulating hemoglobin
Cardiac muscles store oxygen in myoglobin