Gas Exchange

2 Places where gas exchange occurs

1. External respiration: Alveoli

   O₂ to blood, CO₂ to lungs

2. Internal respiration: Blood vessels (capillaries)

   CO₂ to blood, O₂ to tissues

Do gases travel down a concentration gradient?

No, gases travel down a pressure gradient, and each have their own partial pressure, not concentration

Dalton’s Law

Total air pressure is the sum of the partial pressures of each component gas added together.

Air pressure

Air pressure (total) at sea level = 760mmHg

• pO₂ = 160 mmHg

• pCO₂ = 0.3 mmHg

1. O₂ & CO₂ is outside at normal air pressure

2. Air travels through the conducting zones, becomes humidified and warmed up, mixes with the stale air (residual volume in lungs) and arrives at the alveoli.

3. Venous blood in the veinules wrapping the alveoli, has a specific partial pressure to prompt O₂ into the blood and CO₂ out of the blood

4. Pressure of the blood changes as it becomes arterial blood (same O₂ & CO₂ partial pressure as in the alveolus.

5. Capillaries arrive at tissue sites and gas exchange occurs again, has a specific partial pressure to prompt CO₂ into the blood and O₂ into the tissues.

6. The deoxygenated blood that enters the capillaries has the same pressure as the venous blood.