Cardiovascular and respiratory systems — AQA GCSE Physical Education revision

Heart structure and cardiac output

• The heart has four chambers: right atrium, right ventricle, left atrium, left ventricle. Deoxygenated blood enters the right atrium, and oxygenated blood leaves the left ventricle.
• Double circulation means blood passes through the heart twice per full circuit: pulmonary circulation (heart to lungs and back) and systemic circulation (heart to body and back).
• Cardiac output (Q) = stroke volume (SV) × heart rate (HR); it is measured in litres per minute.
• Vascular shunting (redistribution of blood) diverts blood away from non-essential organs (e.g. digestive system) towards working muscles during exercise, using vasodilation and vasoconstriction.
• Regular aerobic training causes cardiac hypertrophy, increasing stroke volume, which can lower resting heart rate over time.

Blood vessels and gaseous exchange

• Arteries carry oxygenated blood away from the heart (except the pulmonary artery) under high pressure, with thick muscular/elastic walls.
• Veins carry deoxygenated blood back to the heart (except the pulmonary vein) at low pressure and contain valves to prevent backflow.
• Capillaries are one cell thick, allowing efficient gaseous exchange of oxygen and carbon dioxide between blood and tissues/alveoli.
• Air pathway: nose/mouth → trachea → bronchi → bronchioles → alveoli, where gaseous exchange occurs by diffusion.
• At the alveoli, oxygen diffuses into the blood (down a concentration gradient) and carbon dioxide diffuses out into the alveoli to be exhaled.

Key terms

Cardiac output

Volume of blood pumped by the heart per minute; SV × HR.

Stroke volume

The volume of blood pumped out of the heart per beat.

Heart rate

Number of times the heart beats per minute.

Vascular shunting

Redistribution of blood flow towards working muscles during exercise.

Double circulation

Blood passes through the heart twice per full circuit of the body (pulmonary and systemic).

Alveoli

Tiny air sacs in the lungs where gaseous exchange occurs.

Common exam traps

• Mixing up arteries and veins — arteries carry blood away from the heart, veins carry it back, regardless of oxygenation (except pulmonary vessels).
• Forgetting the pulmonary artery carries deoxygenated blood and the pulmonary vein carries oxygenated blood — the exception to the usual rule.
• Confusing tidal volume (normal breath) with vital capacity (maximum forced breath).

Practice questions with answers

1. 1. What is the equation for cardiac output?

   • • Stroke volume ÷ heart rate
   • • Stroke volume × heart rate
   • • Heart rate − stroke volume
   • • Heart rate ÷ stroke volume

   Answer: Stroke volume × heart rate

   Cardiac output = stroke volume × heart rate.

2. 2. A performer has a stroke volume of 70ml and a heart rate of 150bpm. Calculate cardiac output in ml/min.

   Answer: 10,500 ml/min

   Cardiac output = SV × HR = 70 × 150 = 10,500 ml/min.

3. 3. Which blood vessel carries oxygenated blood from the lungs to the heart?

   • • Pulmonary artery
   • • Pulmonary vein
   • • Aorta
   • • Vena cava

   Answer: Pulmonary vein

   The pulmonary vein is unusual in carrying oxygenated blood, from the lungs to the left atrium.

4. 4. What is vascular shunting?

   • • Blood clotting in vessels
   • • Redistribution of blood towards working muscles
   • • The heart beating irregularly
   • • Air entering the bloodstream

   Answer: Redistribution of blood towards working muscles

   Vascular shunting diverts blood from less active areas towards working muscles during exercise.

5. 5. Give the correct order of the pathway of air from mouth to alveoli.

   Answer: Mouth/nose, trachea, bronchi, bronchioles, alveoli

   Air travels through the trachea, then bronchi, then bronchioles, before reaching the alveoli.

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