PE4: The Cardio-Respiratory System
Pathway of air, gaseous exchange, heart structure, double circulatory system and blood vessels.
🌬️ Pathway of Air
Key Sequence: Air travels through the respiratory system in this exact order: Nose → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli
Each structure has a specific function in preparing air for gaseous exchange:
| Structure | Description | Function |
|---|---|---|
| Nose | Two nasal passages with hairs and mucous membrane | Filters dust and bacteria; warms and moistens the air |
| Pharynx (throat) | Muscular tube shared with digestive system | Passageway for air to the larynx |
| Larynx (voice box) | Contains vocal cords; epiglottis on top | Epiglottis prevents food entering the trachea; produces sound |
| Trachea (windpipe) | Tube with C-shaped cartilage rings; lined with cilia and mucus | Carries air to the bronchi; cartilage prevents collapse; cilia move mucus and trapped particles upward |
| Bronchi | Two branches (left and right) from the trachea | Carry air into each lung; also lined with cartilage and cilia |
| Bronchioles | Smaller branches within each lung | Distribute air throughout the lungs; smooth muscle controls diameter |
| Alveoli | Tiny air sacs at the end of bronchioles; surrounded by capillaries | Site of gaseous exchange between air and blood |
Pathway of Air Mnemonic: N-P-L-T-B-B-A
Nose → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli
Nose → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli
🫁 Gaseous Exchange
Definition: Gaseous exchange is the diffusion of gases between the alveoli and the blood in the surrounding capillaries. Oxygen moves from the alveoli into the blood, and carbon dioxide moves from the blood into the alveoli.
Gaseous exchange occurs by diffusion - the movement of molecules from an area of high concentration to an area of low concentration.
- Oxygen diffuses from the alveoli (high O₂ concentration) into the blood (low O₂ concentration)
- Carbon dioxide diffuses from the blood (high CO₂ concentration) into the alveoli (low CO₂ concentration)
Features that make alveoli efficient for gaseous exchange:
- Large surface area - approximately 70m² (roughly the size of a tennis court)
- Thin walls - alveoli and capillary walls are each one cell thick, creating a very short diffusion distance
- Moist lining - gases dissolve in the moisture before diffusing
- Dense capillary network - ensures constant blood flow for efficient exchange
- Good ventilation - constant supply of fresh air maintains the concentration gradient
❤️ Heart Structure
The heart is a muscular pump with four chambers: two atria (upper, receiving chambers) and two ventricles (lower, pumping chambers). It is divided into a right side (pumping deoxygenated blood to the lungs) and a left side (pumping oxygenated blood to the body).
| Chamber | Function | Blood Type |
|---|---|---|
| Right atrium | Receives deoxygenated blood from the body via the vena cava | Deoxygenated |
| Right ventricle | Pumps deoxygenated blood to the lungs via the pulmonary artery | Deoxygenated |
| Left atrium | Receives oxygenated blood from the lungs via the pulmonary vein | Oxygenated |
| Left ventricle | Pumps oxygenated blood to the body via the aorta | Oxygenated |
Why the left ventricle has the thickest wall: The left ventricle must pump blood to the entire body (systemic circulation), requiring much higher pressure than the right ventricle, which only pumps blood to the nearby lungs (pulmonary circulation).
Heart Valves
Valves prevent the backflow of blood, ensuring it flows in one direction:
- Tricuspid valve - between right atrium and right ventricle
- Bicuspid (mitral) valve - between left atrium and left ventricle
- Semilunar valves - in the aorta and pulmonary artery, preventing backflow into the ventricles
Remember: Arteries carry blood AWAY from the heart. Veins carry blood TOWARDS the heart. The pulmonary artery is the only artery carrying deoxygenated blood. The pulmonary vein is the only vein carrying oxygenated blood.
🔄 The Double Circulatory System
Key Concept: Humans have a double circulatory system - blood passes through the heart twice for each complete circuit of the body. This allows blood to be pumped at a much higher pressure, delivering oxygen more efficiently.
1. Pulmonary Circulation
The right side of the heart pumps deoxygenated blood to the lungs:
- Right ventricle → Pulmonary artery → Lungs (gaseous exchange) → Pulmonary vein → Left atrium
- Blood picks up oxygen and releases carbon dioxide in the lungs
2. Systemic Circulation
The left side of the heart pumps oxygenated blood to the body:
- Left ventricle → Aorta → Body tissues (oxygen delivered) → Vena cava → Right atrium
- Blood delivers oxygen and nutrients to tissues; picks up carbon dioxide and waste
Why Double Circulation Matters in Sport
During exercise, the double circulatory system is vital. The left ventricle pumps oxygenated blood at high pressure through the aorta to working muscles. After muscles use the oxygen, deoxygenated blood returns to the right side of the heart, is sent to the lungs to pick up more oxygen, then returns to the left side to be pumped out again. This efficient cycle allows sustained aerobic exercise like a 1500m run.
🩸 Blood Vessels
| Feature | Arteries | Veins | Capillaries |
|---|---|---|---|
| Function | Carry blood away from the heart | Carry blood towards the heart | Exchange of materials between blood and tissues |
| Wall thickness | Thick (muscle and elastic tissue) | Thin (some muscle and elastic tissue) | One cell thick (endothelium only) |
| Lumen size | Small lumen | Large lumen | Very small (only one red blood cell at a time) |
| Pressure | High pressure | Low pressure | Very low pressure |
| Valves | No valves | Valves present (prevent backflow) | No valves |
| Key example | Aorta, pulmonary artery | Vena cava, pulmonary vein | Surrounding alveoli and muscles |
Capillary adaptation for exchange: Capillary walls are only one cell thick, creating a very short diffusion distance. This allows oxygen, carbon dioxide, glucose and waste products to diffuse efficiently between the blood and body tissues.
Blood Vessels During Exercise
During exercise, vasodilation (widening) of arteries and arterioles supplying working muscles increases blood flow, delivering more oxygen and glucose. Simultaneously, vasoconstriction (narrowing) of vessels to less essential organs (like the digestive system) redirects blood towards the muscles.
🧪 Composition of Blood
| Component | Function |
|---|---|
| Red blood cells (erythrocytes) | Carry oxygen using haemoglobin; contain no nucleus (more room for haemoglobin); biconcave disc shape (increases surface area) |
| White blood cells (leucocytes) | Defend the body against infection; produce antibodies; engulf pathogens (phagocytosis) |
| Platelets (thrombocytes) | Help blood clot at wound sites; prevent excessive bleeding and entry of pathogens |
| Plasma | Liquid part of blood; transports dissolved substances: glucose, hormones, carbon dioxide, urea, amino acids and antibodies |
❓ Practice Questions
Q1: Describe the pathway of air from the nose to the alveoli.
Q2: Explain three features of alveoli that make them efficient for gaseous exchange.
Q3: Why does the left ventricle have a thicker muscular wall than the right ventricle?
Q4: Describe the difference between pulmonary circulation and systemic circulation.
Q5: Compare the structure of arteries, veins and capillaries.
Q6: Why do veins contain valves but arteries do not?
✅ Answers
- Nose → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli. Each structure filters, warms or channels the air towards the alveoli where gaseous exchange occurs.
- Large surface area (approximately 70m²) allows a high rate of diffusion. Thin walls (one cell thick for both alveoli and capillaries) create a short diffusion distance. Moist lining allows gases to dissolve before diffusing. Dense capillary network maintains the concentration gradient with constant blood flow.
- The left ventricle pumps blood through the aorta to the entire body (systemic circulation), requiring high pressure. The right ventricle only pumps blood to the nearby lungs (pulmonary circulation), which requires much lower pressure.
- Pulmonary circulation carries deoxygenated blood from the right ventricle to the lungs via the pulmonary artery, and returns oxygenated blood to the left atrium via the pulmonary vein. Systemic circulation carries oxygenated blood from the left ventricle to the body via the aorta, and returns deoxygenated blood to the right atrium via the vena cava.
- Arteries have thick walls (muscle and elastic tissue), small lumens and high pressure, with no valves. Veins have thinner walls, larger lumens and lower pressure, with valves to prevent backflow. Capillaries are one cell thick with very small lumens, allowing exchange of materials with tissues.
- Veins carry blood at low pressure back to the heart. Without valves, gravity and low pressure would cause blood to pool or flow backwards, especially in the legs. Arteries carry blood at high pressure, generated by the heart, so the pressure itself prevents backflow and valves are unnecessary.
🎯 Exam Tips
- Use the exact pathway sequence - missing a step loses marks
- Remember: pulmonary artery = deoxygenated, pulmonary vein = oxygenated (the exceptions)
- When describing gaseous exchange, always mention diffusion and the concentration gradient
- Know the four chambers of the heart and whether they carry oxygenated or deoxygenated blood
- Be prepared to explain why the left ventricle has the thickest wall
- Capillaries being "one cell thick" is a key phrase examiners look for
⚠️ Common Errors
Watch Out!
Students often say all arteries carry oxygenated blood. Wrong: "Arteries always carry oxygenated blood." Correct: "Arteries carry blood away from the heart. The pulmonary artery carries deoxygenated blood."
Students often confuse the bicuspid and tricuspid valve positions. Wrong: "The tricuspid valve is on the left side." Correct: "The tricuspid valve is between the right atrium and right ventricle."
📝 Exam Technique
PE Exam Tips — The Cardio-Respiratory System:
1. For The Cardio-Respiratory System questions, use subject-specific terminology precisely
2. Support every point with specific evidence or examples
3. Show balanced analysis — consider different perspectives before reaching a conclusion
4. Link your understanding of The Cardio-Respiratory System to real-world contexts where possible
5. For longer answers, plan your response to address all parts of the question
1. For The Cardio-Respiratory System questions, use subject-specific terminology precisely
2. Support every point with specific evidence or examples
3. Show balanced analysis — consider different perspectives before reaching a conclusion
4. Link your understanding of The Cardio-Respiratory System to real-world contexts where possible
5. For longer answers, plan your response to address all parts of the question
⚠️ Common Errors
Watch Out!
Students often think lactic acid causes doms. Wrong: Lactic acid causes DOMS Correct: DOMS (delayed onset muscle soreness) is caused by micro-tears in muscle fibres, not lactic acid. Lactic acid is cleared within an hour of exercise.
Students often think veins always carry deoxygenated blood. Wrong: Veins always carry deoxygenated blood Correct: Pulmonary veins carry oxygenated blood from the lungs to the heart. It is arteries and veins relative to the heart that matters, not oxygenation.
Students often think the heart beats faster during exercise just because you need more oxygen. Wrong: The heart beats faster during exercise just because you need more oxygen Correct: Heart rate increases due to anticipatory rise (before exercise), increased CO2 in blood detected by chemoreceptors, and decreased vagal tone. It is a coordinated response, not just oxygen demand.
✍️ Model Answer
Full-Mark Response
6 marks: Explain how the cardio-respiratory system affects sporting performance.
The Cardio-Respiratory System has significant effects on sporting performance. [Key concept 1]: explain the mechanism with specific detail. [Key concept 2]: how this applies in a named sporting example. [Key concept 3]: the relationship between this topic and overall performance. A grade 9 answer uses precise anatomical/physiological terminology, specific sporting examples, and evaluates the relative importance of different factors.
Mark scheme: 2 marks per explained point with specific evidence, evaluation for top marks
📊 AO Deep Dive
Assessment Objective Analysis
GCSE PE tests four AOs: AO1 (Knowledge, 30%) — recall facts about The Cardio-Respiratory System including definitions, classifications and specific examples; AO2 (Application, 30%) — apply knowledge to sporting contexts and training scenarios; AO3 (Analysis and Evaluation, 25%) — analyse data (graphs, tables), evaluate training methods or strategies, and justify recommendations; AO4 (Practical, 15%) — demonstrate relevant skills. For grade 9, use precise terminology, support every point with named sporting examples, and evaluate rather than just describe. The difference between grade 5 and grade 9 is the quality of application and depth of evaluation.
📝 Exam Questions by Topic
🎬 Video Resources
Ready to ace your GCSE PE exams?
Get the best revision books and guides to boost your grades.