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The Cardiovascular System

The cardiac cycle and control of heart rate

  • 3 things to know
  • A2 2

Overview

Diastole, atrial and ventricular systole, heart sounds, cycle length calculations, the ECG, the cardiac control centre, sympathetic and parasympathetic control, receptors and adrenaline.

What you need to know

Answer each one before you reveal it.

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Key term

What is the cardiac cycle?

Key term

Describe what happens during diastole.

Key term

Describe atrial systole.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is the cardiac cycle?

    Model answer

    The cardiac cycle is the sequence of events in one complete heartbeat. The cycle has a relaxation phase called diastole and a contraction phase called systole.

  2. 2

    Describe what happens during diastole.

    Model answer

    Diastole is the phase in which the atria and ventricles relax and fill with blood. The atrioventricular valves are open and the semilunar valves are closed.

  3. 3

    Describe atrial systole.

    Model answer

    Atrial systole is the contraction of the atria. The contraction pushes the remaining blood through the open atrioventricular valves into the ventricles.

  4. 4

    Describe ventricular systole.

    Model answer

    The ventricles contract, closing the atrioventricular valves and forcing the semilunar valves open. Blood is ejected into the aorta and pulmonary artery.

  5. 5

    What causes the two sounds of a heartbeat?

    Model answer

    The first sound is the atrioventricular valves closing as ventricular systole begins. The second sound is the semilunar valves closing as diastole begins.

  6. 6

    How long does one cardiac cycle last at rest?

    Model answer

    One cycle lasts 0.8 seconds at a resting heart rate of 75 beats per minute. Diastole takes about 0.5 seconds and systole about 0.3 seconds.

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AThe target heart rate is about 168 bpm.
BMaximum heart rate is 220 − 18 = 202 bpm.
CThe working is 0.75 × (202 − 65) + 65 = 167.75 bpm.

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