Download Heart Function – Cardiac Cycle and the Electrocardiogram (ECG)

Heart Function – Cardiac Cycle and the
Electrocardiogram (ECG)
R. Atrium
Pulmonary Artery
R. Ventricle
TCV
PSLV
Vena Cava
Lungs
Aorta
ASLV
L. Ventricle
BCV
L. Atrium
Pulmonary Vein
Pathway of Blood – Pulmonary and Systemic
Circuits
Cardiac Cycle
All the changes that occur during one heartbeat – one cycle of
contraction/ relaxation (systole/diastole)
Measurable changes include:
• Pressure
• Volume
• Heart sounds
• Electrical impulses
Blood flows through the heart based on pressure differences
• Pressure differences caused by changes in volume
• Changes in volume caused by heart contractions
• Heart contractions caused by depolarization of muscle cells
Cardiac Cycle
Electrical
Changes
•Cause
Contraction
Contraction
•Decreases
Volume
Volume
Change
•Increases
Pressure
Pressure
Change
•Opens Valve
Blood
Moves
•High to
Low
Pressure
Cardiac Cycle


Systole = contraction
Diastole = relaxation

Atrial Systole = atrial contraction
 atrial pressure > ventricular pressure
 AV valves open
 semi-lunar valves close

Ventricular Systole = ventricular contraction
 ventricular pressure > atrial pressure
 semi-lunar valves open
 AV valves close
Cardiac Cycle
 Describe the pressure graph
using time and phase
 Describe the volume graph
using time and phase
 Describe the ECG graph using
time and phase
 Describe the heart sound
graph using time and phase
Figure 13.10
Cardiac Cycle
Click here for video clip of Cardiac Cycle
Click here for a video clip of a normal heart beat
Heart Conduction System
Intrinsic Conduction (conduction from within)
 Heart contractions occur independently of the nervous system.
 Electrical stimulation begins in the SA node, the ‘pacemaker’.
 The electrical pathway:
SA node AV node Right and Left Bundle Branches
Purkinje Fibers
Figure 13.11
Heart Conduction System
Click here for video clip of Heart Conduction System
Heart Conduction System
How an Impulse is Conducted-The Action Potential
1. Heart Muscle Cell--Polarized
++++++++
------------------------++++++++
2. Heart Muscle Cell--Depolarized
*caused by movement of ions
3.
Heart Muscle Cell –-(Re)polarized
+-+-+-+--+-+-+-+
-+--+--++-+-+-+-
++++++++
------------------------++++++++
Outside cell
Inside cell
Outside cell
*When cells
depolarize, they
contract.
*When many cells
depolarize, the
heart contracts.
The Electrocardiogram (ECG)
 Measures electrical conduction throughout the cardiac cycle
 Works by measuring electrical changes of de- and re-polarization
 Sequence:
• Atria contract (de-)
• Atria relax (re-)
• Ventricles contract (de-)
• Ventricles relax (re-)
Figure 13.14
The Electrocardiogram (ECG)
Abnormal ECG’s
Figure 13.15
ECG and Cardiac Cycle
Click here for a video clip of a normal heart beat
Click here for a video clip of an abnormal heart
beat – ventricular fibrillation