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7.3 GASEOUS EXCHANGE ACROSS THE RESPIRATORY SURFACES & TRANSPORT OF GASES IN HUMANSTransport of oxygen & carbon dioxide

Characteristics of the respiratory surface in the alveoli :Large surface areamoist epithelial surface Thin one cell thick Underlying capillary networkExchange of gases is through diffusionGases diffuse down their partial pressure gradients

Gaseous exchange in alveolusTransport of oxygenTransport of oxygenOxygen is transported from the lungs in two ways:

As oxyhaemoglobin in RBC (99%)

In lungs (high PO2 )

In tissue

b) As dissolved gas molecules in the plasma

Hb + 402 Hb (O2)4(Haemoglobin) (oxygen) (oxyhaemoglobin)Hb (O2)4 Hb + 4 O2 Oxyhaemoglobin Haemoglobin oxygen Transport of CARBON DIOXIDETransport of CO2 from the lungsAs bicarbonate ion (85%)Formation of bicarbonate ion

- When deoxygenated blood reaches lungs:

When deoxygenated blood reaches lungs:

CO2 + H20 H2CO3 HC03- + H- (Carbonic acid) (Bicarbonate ion)HCO3- + H+ H2CO3 CO2 + H2O(Carbonic acid)2. Combines with RBC to form carbaminohaemoglobin

Formation of carbaminohaemoglobinHigh P CO2

When reaches lungsLow P CO2

Hb + CO2 HbCO2 HbCO2 Hb + CO23. Dissolved in the blood plasma transported as dissolved gas moleculesWhen reaches lung; diffuse into the alveolar air7.4 THE REGULATORY MECHANISM OF OXYGEN & CARBON DIOXIDE CONTENTS IN BODY