Heart Function – Cardiac Cycle and the Electrocardiogram (ECG)

Pathway of Blood – Pulmonary and Systemic Circuits R. Atrium R. Ventricle Pulmonary Artery TCV PSLV Vena Cava Lungs Aorta ASLV BCV L. Ventricle 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 Contraction Volume Change 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 ++++++++ ------------- Outside cell 1. Heart Muscle Cell--Polarized Inside cell Outside cell +-+-+-+- --+-+-+-+ -+--+--+- Heart Muscle Cell--Depolarized *caused by movement of ions *When cells depolarize, they contract. *When many cells depolarize, the heart contracts. ++++++++ ------------- 3. Heart Muscle Cell –-(Re)polarized

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