How Does Exchange of Oxygen And Carbon-di-Oxide Happen?

Pranayama is basically a breathing process done with certain speed and rhythm. We shall, however, first consider the normal breathing. The normal respiration is done for supplying O2 (from atmosphere) to blood and in turn, to enormous number of cells and evacuating the C02 generated in the energy process of the cells. The gas exchange (O2 to blood capillaries and uptake of CO2 from impure blood in the capillaries) takes place at the lungs.
The figure shows the major (general) pathway of air during breathing. Most of the air inhaled through nostrils passes through the pathway shown but a very small portion of the inhaled air passes through flow path above the roof of the nasal cavity. This air plays a very important role as we shall see later.

The air inhaled through nostrils get properly filtered and conditioned from the point of view of temperature and humidity. The inhaled air passes through the pharynx, trachea and the primary bronchi. Subsequently the air flows through tertiary bronchi to which are attached innumerable alveoli, which serve the purpose of sites of gas exchange .

Lung structure and gas exchange

  • It is very interesting to note the following information about the lung structure and alveoli which are very tiny grape like structures.
  • There are more than 300 million alveoli surrounded by blood capillaries in the lung structure. The entire blood of the body comes here for purification (oxygenation).
  • The surface area of these is of the order of 75 -100 square meters.
  • Exchange of O2 and CO2 with blood in the capillaries surrounded by alveoli take place by diffusion.
  • The diffusion process is very efficient since the walls of capillaries as well as that of alveoli are very thin.
  • Diffusion occurs because of partial pressure gradient. Larger is this gradient, higher will be the extent of gas exchange
  • Lung structure does contain dead pockets of the size of 150 ML where no gas exchange process takes place.

Process of Exchange of Gases

The process of gas exchange is explained in figure . Figure (a) shows O2 transfer (from one typical alveolus) to the impure blood (blue) and making it oxygenated (red). The figure also shows transfer of blue blood CO2 to a typical alveolus.


The CO2 of impure blood in all the capillaries spread over the surface of alveoli is transferred to alveoli and then to bronchi and ultimately expelled out during exhalation phase of the breathing.
Figure ( b) show the gas exchange process from and to capillaries from a typical cell. The oxygenated blood (red) supplies O2 to the cell and CO2 from cell (released from energy production process) is transferred to the blood which, as it passes the cell, becomes blue because of C02 pick-up.
It is very easy now to understand that any action which increases O2 pick up and CO2 expulsion by lungs will result into abundant supply of 02 to blood and very effective scavenging of CO2 that gets generated in the cell process. At this stage it is very important to understand the physiological effects of Oxygen uptake by the cells or what can be called the “oxygen metabolism”.

Leave a Reply

Your e-mail address will not be published. Required fields are marked *