Exchange of Gases: Exchange of gases takes place at two sites

• Alveoli to blood
• Between blood and tissues.

Diagrammatic representation of exchange of gases at the alveolus and the body tissues with blood and transport of oxygen and carbon dioxide

• Exchanges of gases occur by simple diffusion due to pressure/ concentration gradient, solubility of the gases and thickness of membrane.
• Pressure contributed by individual gas in a mixture of gas is called partial pressure represented by pC and p .
• Partial pressure of Oxygen and carbon dioxide at different part involved in diffusion varies from one part to another and moves from higher partial pressure to lower partial pressure.
• Solubility of C is 20-25 times more than solubility of  , so C diffuse much faster through membrane.
• Diffusion membrane is three layered thick, that is alveolar squamous epithelium, endothelium of alveolar capillaries and basement substance between them.

Transport of Gases

• Blood is the medium of transport for C and  . Most of oxygen (97%) is transported through RBC and remaining 3% by blood plasma.
• 20-25% of C is transported by RBC, 70% as bicarbonate and rest 7% in dissolved state by blood plasma.

Transport of Oxygen

• Haemoglobin in RBC combines with  to form Oxyhaemoglobin. Each haemoglobin combine with four oxygen molecules.
• Binding of  is related with partial pressure of  and , hydrogen ion concentration and temperature.
• Percentage saturation of haemoglobin and partial pressure of oxygen forms sigmoid curve (oxygen dissociation curve).
• In the alveoli, p is more and pC is less, less H+ ions concentration and lower temperature favour the binding of  with hemoglobin. Where opposite condition in tissues favour the dissociation of Oxyhaemoglobin.

Transport of Carbon dioxide

• Carbon dioxide is transported by haemoglobin as carbamino-haemoglobin. In tissues pC is high and p is less that favour the binding of carbon dioxide with haemoglobin. Opposite condition help in dissociation of carbamino- haemoglobin in alveoli.
• Enzyme carbonic anhydrase help in formation of carbonate ions to transport carbon dioxide.

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By Team Learning Mantras