## Exchange of Gases – Class 11 | Chapter – 17 | Biology Short Notes Series PDF

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${O_2}$ and p${O_2}$ .
• 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${O_2}$ is 20-25 times more than solubility of ${O_2}$ , so C${O_2}$ 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${O_2}$ and ${O_2}$ . Most of oxygen (97%) is transported through RBC and remaining 3% by blood plasma.
• 20-25% of C${O_2}$ is transported by RBC, 70% as bicarbonate and rest 7% in dissolved state by blood plasma.

Transport of Oxygen

• Haemoglobin in RBC combines with ${O_2}$ to form Oxyhaemoglobin. Each haemoglobin combine with four oxygen molecules.
• Binding of ${O_2}$ is related with partial pressure of ${O_2}$ and ${CO_2}$, hydrogen ion concentration and temperature.
• Percentage saturation of haemoglobin and partial pressure of oxygen forms sigmoid curve (oxygen dissociation curve).
• In the alveoli, p${O_2}$ is more and pC${O_2}$ is less, less H+ ions concentration and lower temperature favour the binding of ${O_2}$ 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${O_2}$ is high and p${O_2}$ 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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