1.3 Explain the interrelationship between the respiratory and circulatory systems and movement

1. Structure and function of both systems

To explain the interrelationship, link structure to function, then follow the continuous pathway from air to muscles and back again. The respiratory system is the site where gases move between air and blood. The circulatory system is the transport network that delivers oxygen to tissues and returns carbon dioxide to the lungs.

Sequence that links structure to function:

• Ventilation moves air to the alveoli.
• Diffusion moves gases between alveoli and lung capillaries.
• Transport distributes oxygen to muscles and returns carbon dioxide for removal.

1.1 The respiratory system: structure and function for movement

The respiratory system moves air into and out of the lungs and provides a large, efficient surface for gaseous exchange. During movement, ventilation increases, so any narrowing or irritation in the airways can reduce oxygen uptake.

Major respiratory structures and movement related functions:

• Nose and nasal cavity
  • Air is warmed, moistened, and filtered.
  • Filtering helps reduce irritation during sustained exercise.
• Pharynx
  • Directs air from the nose and mouth towards the trachea.
• Epiglottis
  • Closes over the trachea during swallowing to prevent food entering the airway.
• Larynx
  • Helps protect the airway by triggering coughing if food or fluid enters.
• Trachea
  • Cartilage rings help keep it open.
  • Lined with mucus and cilia that trap and move particles away from the lungs.
• Bronchi and bronchioles
  • The trachea divides into two bronchi, then branches into smaller bronchioles.
  • This spreads airflow so many exchange sites receive ventilation at once.
• Alveoli
  • Microscopic air sacs at the ends of the smallest bronchioles.
  • One cell thick walls, surrounded by many capillaries.
  • This gives a short distance for diffusion of oxygen and carbon dioxide.
  • Adults have roughly 500 million alveoli, with a large total surface area (around 100 m²) for efficient exchange.
• Diaphragm and intercostal muscles
  • Drive breathing by changing chest volume.
  • Contraction draws air in and relaxation pushes air out.
  • This is ventilation, which keeps oxygen available in the alveoli for diffusion into the blood.

Because lungs are exposed to the outside air, pollutants and infections can reduce airflow and gaseous exchange. Avoiding smoking and reducing exposure to pollutants supports respiratory efficiency during exercise. Regular aerobic training can strengthen breathing muscles and improve how well ventilation and blood flow match in the lungs, supporting more efficient gas exchange.

Example: In a steady jog, breathing through the nose helps warm and filter air. In cold, dry conditions, mouth breathing can irritate airways for some people and make it harder to keep a steady pace.

1.2 The circulatory system: structure and function for movement

The circulatory system, also called the cardiovascular system, is the body’s transport network. It includes blood, the heart, and blood vessels. During movement, its main job is to deliver oxygen and nutrients to working tissues and remove carbon dioxide, heat, and other wastes. Oxygen that enters the body through the lungs only helps movement if the circulatory system can transport it to the muscles.

• Blood
  • About 5 litres circulates through the body in an adult.
  • For movement, red blood cells are especially important because they contain haemoglobin.
  • Haemoglobin binds oxygen in the lungs, transports it to tissues for ATP production, and helps with the return transport of carbon dioxide.
• Heart
  • Muscular pump in the chest.
  • Right and left sides, each with an atrium and a ventricle.
  • Valves prevent backflow so blood moves in one direction.
  • During exercise, heart rate increases and stroke volume often increases.
  • This raises cardiac output, so more oxygenated blood is delivered each minute.
• Blood vessels
  • Arteries carry blood away from the heart under higher pressure.
  • Capillaries are the thin exchange vessels where oxygen and carbon dioxide move by diffusion.
  • Veins return blood to the heart under lower pressure and often have valves to reduce backflow.

Example: In a fast netball quarter, blood flow increases to working muscles for oxygen delivery. Blood flow to the skin also increases so heat can be released.

1.3 How they work together to support movement

The respiratory and circulatory systems form one linked pathway that matches oxygen supply and carbon dioxide removal to the needs of movement. The respiratory system provides effective ventilation and the exchange surface in the lungs. The circulatory system provides blood flow to the lungs and transport to the muscles.

If either part is limited, performance drops:

• Without effective ventilation, oxygen in the alveoli falls and diffusion into the blood slows.
• Without effective circulation, oxygen cannot reach muscles and carbon dioxide cannot return to the lungs.

This interrelationship relies on three connected processes:

• Ventilation maintains higher oxygen and lower carbon dioxide in alveolar air.
• Diffusion moves gases across the thin alveolar capillary membrane.
• Transport moves oxygenated blood to muscles and returns carbon dioxide to the lungs.

Example: If ventilation increases but cardiac output is low, oxygen uptake is still limited because diffusion depends on both air flow and blood flow in the lungs. If cardiac output increases but airways are narrowed, blood cannot pick up as much oxygen in the lungs, so delivery to muscles is reduced.

2. Pulmonary and systemic blood circulation and gaseous exchange

The circulatory system has two connected circuits that support movement. Pulmonary circulation sends blood from the heart to the lungs for gaseous exchange. Systemic circulation sends oxygenated blood from the heart to the rest of the body. Both loops run continuously and speed up during movement so oxygen uptake and delivery can match higher demand.

These loops matter because they ensure:

• blood is re oxygenated in the lungs
• oxygenated blood reaches muscles for aerobic ATP production
• carbon dioxide produced by muscles is returned to the lungs for removal

2.1 Pulmonary circulation: heart → lungs → heart

Pulmonary circulation moves blood from the heart to the lungs and back so it can pick up oxygen and release carbon dioxide.

Pulmonary circulation pathway:

• Deoxygenated blood returns to the right atrium.
• Blood flows into the right ventricle.
• The right ventricle pumps blood through the pulmonary arteries to the lungs.
  • Important exception: pulmonary arteries carry deoxygenated blood because they go from heart to lungs.
• In lung capillaries around alveoli:
  • carbon dioxide diffuses from blood into alveolar air
  • oxygen diffuses into the blood and binds to haemoglobin
• Oxygenated blood returns via the pulmonary veins.
  • Another exception: pulmonary veins carry oxygenated blood from lungs to heart.
• Blood enters the left atrium ready for systemic circulation.

Pulmonary circulation reloads blood with oxygen so it can support movement. If ventilation or alveolar exchange is reduced, blood leaves the lungs with less oxygen, even if the heart is pumping strongly.

Example: During repeated sprints, pulmonary circulation must keep up with rapid changes in ventilation and oxygen demand. If exchange is impaired, oxygen saturation can drop and breathlessness happens earlier.

2.2 Systemic circulation: heart → body → heart

Systemic circulation sends oxygenated blood from the heart to the body and returns deoxygenated blood back to the heart. During movement, it delivers oxygen to muscles and collects carbon dioxide produced by metabolism.

Systemic circulation pathway:

• Oxygen rich blood moves from the left atrium into the left ventricle.
• The left ventricle pumps blood into the aorta.
• Blood travels through systemic arteries to organs and working muscles.
• In tissue capillaries:
  • oxygen diffuses into cells for ATP production
  • carbon dioxide diffuses into the blood
• Blood returns through veins into the superior and inferior vena cava.
• Blood returns to the right atrium.

Systemic circulation supplies tissues and removes wastes. During exercise, it also helps with heat removal by increasing blood flow to the skin when needed.

Example: When intensity increases from walking to running, more systemic blood flow is directed to the working muscles to support faster ATP turnover.

2.3 Gaseous exchange: external (alveoli) and internal (tissues)

Gaseous exchange swaps oxygen and carbon dioxide between air and blood, and between blood and tissues. It happens by diffusion across thin membranes. The respiratory system provides the alveoli as the exchange surface. The circulatory system provides blood flow and haemoglobin to make this exchange useful for movement.

Two exchange sites:

• External gaseous exchange (lungs)
  • Between alveolar air and lung capillary blood.
  • Oxygen diffuses into blood and binds to haemoglobin.
  • Carbon dioxide diffuses into the alveoli and is exhaled.
• Internal gaseous exchange (tissues)
  • Between tissue capillaries and body cells, including muscle fibres.
  • Oxygen diffuses into cells for aerobic ATP production.
  • Carbon dioxide diffuses into blood for transport back to the lungs.

As exercise intensity rises, internal exchange increases because muscles use oxygen faster and produce more carbon dioxide. External exchange must also increase so blood leaving the lungs stays oxygen rich.

Example: In the first minutes of hard cycling, muscles rapidly use oxygen and produce carbon dioxide. The lungs must increase external gaseous exchange at the same time, or oxygen delivery cannot keep up.

2.4 How movement increases gaseous exchange and transport

When movement begins, muscles increase oxygen use and carbon dioxide production within seconds. The body responds with acute responses to increase ventilation and circulation so oxygen delivery matches ATP demand.

Acute respiratory responses:

• Breathing rate increases.
• Breathing depth increases.
• Minute ventilation increases.

Acute circulatory responses:

• Heart rate increases.
• Stroke volume often increases.
• Cardiac output increases (heart rate × stroke volume).
• Blood flow is redistributed so working muscles receive a larger share.

Example: In a hard three minute effort, breathing becomes faster and deeper so more oxygen reaches the alveoli. Heart rate rises to increase cardiac output, sending more oxygenated blood to the legs. Carbon dioxide diffuses out of muscles into the blood and is transported back to the lungs for exhalation.

3. Factors that impact on the efficiency of the cardiovascular system

Cardiovascular efficiency is how well the heart and blood vessels deliver oxygen and remove wastes during movement. Good efficiency supports aerobic capacity, delays fatigue, and improves recovery. The syllabus examples each limit a different part of oxygen delivery:

• Altitude reduces oxygen availability.
• Haemoglobin levels set oxygen carrying capacity.
• Vascular disease restricts blood flow and increases resistance.

3.1 Altitude

At higher altitudes, air pressure is lower, so each breath contains less available oxygen. This reduces the diffusion gradient from the alveoli into the blood, so less oxygen is loaded onto haemoglobin. Exercise often feels harder until acclimatised because ventilation and cardiac output increase, but oxygen delivery still drops at higher intensities.

Common short term effects:

• faster breathing at the same pace
• higher heart rate at the same workload
• earlier fatigue

With acclimatisation, the body increases red blood cell production, which can raise haemoglobin concentration and improve oxygen transport.

Example: Training at sea level, then exercising at a ski field, often feels harder in the first few days because less oxygen is available in each breath.

3.2 Haemoglobin levels

Haemoglobin in red blood cells binds oxygen in the lungs and carries it to tissues. Haemoglobin levels matter because they affect how much oxygen can be transported in each litre of blood. Higher haemoglobin generally supports better oxygen delivery and endurance performance.

Low haemoglobin reduces oxygen transport, so the heart often compensates by increasing heart rate to deliver more blood per minute. One cause is iron deficiency anaemia. This can lead to earlier fatigue, breathlessness, and reduced exercise tolerance because muscles receive less oxygen for aerobic ATP production.

Example: Two students run the same test. The student with low haemoglobin may tire sooner because less oxygen is delivered per heartbeat.

3.3 Vascular disease

Vascular disease lowers cardiovascular efficiency when blood vessels narrow, stiffen, or become damaged. This restricts blood flow and increases the resistance the heart must pump against. Atherosclerosis is one example, where plaques build up inside artery walls. If less oxygenated blood reaches working muscles, movement performance drops because aerobic ATP production cannot be maintained as long at higher intensities.

Vascular disease can also reduce oxygen delivery to the heart itself, limiting safe exercise intensity. Risk factors include smoking, high blood pressure, long term poor diet (high saturated fat), and physical inactivity. Regular physical activity and not smoking support vascular health.

Example: A person with early vascular disease may manage light walking but struggle with a sustained run because oxygen delivery to muscles is limited.