Download The Cardiac Cycle

The Cardiac Cycle
Aim:
To understand the Cardiac Cycle
Heart Beat
• A single heart beat is known as the cardiac cycle.
• Atrial Systole is where both atria contract (0.1s)
• Ventricular Systole is where both ventricles contract
forcing blood through the pulmonary artery to the lungs
and through the aorta to the rest of the body (0.3s)
• Atrial diastole is where the atria relax. Blood will enter
the atria from the large veins (0.7s)
• Ventricular diastole is where the ventricles relax, and
start to fill with blood from the atria as the next cycle
begins (0.5s)
• Cardiac Cycle Animation
Stroke Volume and Cardiac Output
• Stroke volume is the volume of blood
pumped by the heart in one cardiac cycle.
• Typically about 80cm3.
• Stroke volume increases during exercise.
• Cardiac Output is the volume of blood
pumped in one minute. It is calculated by
multiplying the stroke volume by the heart
rate. It is expressed in litres of blood per
minute.
Factors Affecting Heart Rate
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Adrenaline.
Movement of limbs (stretch receptors)
Levels of respiratory gases in the blood
Blood pressure – if it gets too high a safety
mechanism prevents heart rate increasing
further.