VCE Physical Education (Year 11) · Unit 1 — The Human Body in Motion · 14m read

The Cardiovascular and Respiratory Systems in Exercise

Your heart and lungs work as a delivery service: oxygen in, carbon dioxide out. During exercise the demand surges, and the way these systems respond explains how fit athletes keep going.

Learning objective: Explain how the cardiovascular and respiratory systems deliver oxygen and remove wastes during exercise.

By the end of this lesson you can:

• I can describe the structure of the heart and blood vessels.
• I can calculate cardiac output.
• I can explain gas exchange at the lungs and muscles.

The cardiorespiratory system is a delivery network. The lungs are the loading dock (oxygen in), the heart is the truck depot, blood vessels are the roads and haemoglobin is the trucks. Exercise is a busy shopping day — everything speeds up.

The Cardiovascular and Respiratory Systems in Exercise

CARDIOVASCULAR SYSTEM:
• Heart — four chambers; left ventricle pumps oxygenated blood to the body.
• Arteries carry blood away from the heart; veins return it; capillaries allow exchange.
• Blood carries oxygen on haemoglobin.

KEY MEASURES:
• HEART RATE (HR) — beats per minute.
• STROKE VOLUME (SV) — blood pumped per beat.
• CARDIAC OUTPUT (Q) = HR × SV (litres per minute).
• Blood pressure, blood redistribution (vasodilation in working muscles).

RESPIRATORY SYSTEM:
• Air path: nose/mouth → trachea → bronchi → bronchioles → alveoli.
• Gas exchange by DIFFUSION at the alveoli and at the muscles.
• VENTILATION (V) = respiratory rate × tidal volume.

THE OXYGEN PATHWAY:
• Lungs → blood → heart → arteries → capillaries → muscle mitochondria.
• VO2 max — the maximum oxygen the body can take in and use per minute.

| Measure | Formula / meaning | Rest → max exercise (trained adult, approx.) |
|---|---|---|
| Heart rate (HR) | Beats per minute | ~70 → ~190 |
| Stroke volume (SV) | mL per beat | ~70 → ~120+ |
| Cardiac output (Q) | Q = HR × SV | ~5 → 20–25 L/min |
| Ventilation (V̇E) | V̇E = RR × TV | ~6 → 100+ L/min |
| a-vO₂ difference | O₂ extracted by muscles | Increases |

Key ideas at a glance

• Q = HR × SV: Learn the formula.
• V̇E = RR × TV: Respiratory rate × tidal volume.
• Gas exchange by diffusion: High to low partial pressure.
• Vascular shunting: Blood redistributed to working muscles.

Key formulas

• Cardiac output: Q = HR \times SV
• Ventilation: V = RR \times TV

Worked example (Easy)

An athlete has HR 150 bpm and SV 120 mL during exercise. Calculate cardiac output.

1. Formula. Q = HR × SV
2. Calculate. 150 × 120 mL = 18 000 mL/min = 18 L/min

Answer: 18 L/min

Worked example (Medium)

Calculate cardiac output if HR = 150 bpm and SV = 110 mL.

1. Formula. Q = HR × SV.
2. Substitute. 150 × 110 = 16 500 mL/min.
3. Convert. 16.5 L/min.

Answer: 16.5 L/min.

Common mistakes

• Saying arteries always carry oxygenated blood The pulmonary artery carries deoxygenated blood. Fix: Arteries carry blood AWAY from the heart.
• Forgetting units in Q Q is in L/min. Fix: Convert mL to L where needed.
• Forgetting units in calculations Loses marks. Fix: Convert mL to L and label.

Vascular shunting

During exercise, vasodilation of arterioles supplying working muscles and vasoconstriction of those supplying organs like the gut redirect blood.

At rest, muscles get about 15–20% of cardiac output; during maximal exercise, around 80–85%.

Practice questions

1. Gas exchange in the lungs occurs at the:

   1. Bronchi
   2. Trachea
   3. Alveoli
   4. Diaphragm

   (1 marks)

2. At rest, HR is 60 bpm and SV is 80 mL. Find Q.

   (2 marks)

3. Cardiac output equals:

   1. HR + SV
   2. HR × SV
   3. RR × TV
   4. SV ÷ HR

   (1 marks)

4. Gas exchange at the alveoli occurs by:

   1. Active transport
   2. Diffusion
   3. Osmosis
   4. Filtration

   (1 marks)

5. Explain why a-vO₂ difference increases during exercise.

   (2 marks)

Summary

• Q = HR × SV; V = RR × TV.
• Gas exchange by diffusion at alveoli and muscles.
• VO2 max reflects aerobic capacity.
• Q = HR × SV; V̇E = RR × TV; shunting redirects blood.