explain transport of gases through blood in humans ?

Transport of Gases − Oxygen and Carbon dioxide

  • Gases transported by blood

  • Oxygen − 97% through RBC
    3% in plasma in dissolved state

  • Carbon dioxide − 20-25% through RBC
    70% as bicarbonate
    7% in plasma in dissolved state

Transport of Oxygen

  • Oxygen binds with haemoglobin to form oxyhaemoglobin.

  • 1 molecule of haemoglobin carries 4 molecules of oxygen.

  • Formation of oxyhaemoglobin depends upon − pO2, pCO2, pH, temperature

  • In alveoli − pO2 (high), pCO2 (low), pH (high) temperature (low) 
    Hence, oxyhaemoglobin forms.

  • In tissues − pO2 (low), pCO2 (high), pH (low) temperature (high)
  • Hence, oxyhaemoglobin dissociates

Transport of Carbon Dioxide


  • CO2 is carried as carbamino-haemoglobin by blood.

  • When pCO2 (high), pO2 (low) − binding of CO2 occurs (as in tissues)

  • When pCO2 (low), pO2 (high) − dissociation of COoccurs (as in alveoli)

  • CO2 is bound with haemoglobin in tissue and dissociates in alveoli where it is released.

  • CO2 is transported as bicarbonate as well.

  • When pCO2 (high), forms (in tissues)

  • When pCO2 (low), CO2 + H2O forms (in Alveoli)

  • CO2 is trapped in tissue as  and released in alveoli.

  • For 100 mL of deoxygenated blood, about 4 mL of CO2 is delivered to alveoli.

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Once the oxygen diffuses across the alveoli, it enters the bloodstream and is transported to the tissues where it is unloaded, and carbon dioxide diffuses out of the blood and into the alveoli to be expelled from the body.
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