Breathing and Exchange of Gases

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SÜRFÅÇË ÅRËÅ

Presence of alveoli increases the surface area of lungs. It increases the gas

exchange.

GÅS TRÅÑSPØRT (Ø2 TRÅÑSPØRT åñd ÇØ2 TRÅÑSPØRT)

It is the transport of respiratory gases (O2 and CO2) from alveoli to the

systemic tissues and vice versa.

Ø2 TRÅÑSPØRT

It is the transport of O2 from lungs to various tissues. It occurs in 2 ways

In physical solution (blood plasma) : About 3% of

O2 is carried in a dissolved state through plasma.

As oxyhaemoglobin : About 97% of O2 is transported

by RBC. O2 binds with haemoglobin (red coloured

iron containing pigment present in the RBCs) to

form oxyhaemoglobin. This is called oxygenation.

Hb has 4 haem units. So, each Hb molecule can

carry 4 oxygen molecules. Binding of O2 depends

upon pO2 , pCO2, H+ ion concentration (pH) and

temperature, are some other factors which can

interfere with this binding.

01

02

In the alveoli, high pO2, low pCO2, lesser H⁺ ion

concentration and lower temperature exist. These factors

are favourable for the formation of oxy-haemoglobin.

In tissues, low pO2 , high pCO2, high H⁺ ions and high

temperature exist. So Hb4O8 dissociates to release O2.

Every 100 ml of oxygenated blood can deliver around

5 ml of O2 to the tissues under normal physiological

conditions.