Mechanism of Human Respiration

Oxygen is required by the cells for oxidising the food and to release the energy. The cells cannot utilise the oxygen directly.

Air is taken into the lungs first and the oxygen present in the air diffuses into the blood and the carbondioxide diffuses out. This part of respiration is called as “External Respiration”.

When the blood enters the tissues, oxygen from the blood diffuses into the tissues and carbondioxide from the tissues diffuses out into the blood. This part of respiration is called as “Tissue Respiration”.

External Respiration

External respiration consists of two stages that includes inspiration and expiration.

1. Inspiration:

Breathing in of the air is called as inspiration. The lungs cannot expand by themselves. Chest cavity has to be enlarged to draw the air into the lungs. It is done by the inter-coastal muscles that are present in the ribs of the chest cavity and the diaphragm.

During the process of inspiration the diaphragm becomes flat, sinks down and pushes the abdominal organs downward allowing the expansion of the chest cavity that results in the decrease of pressure in the chest cavity and helps in drawing of the air into the lungs through the nose, pharynx, larynx and trachea. During this process, sternum moves forward and inter-coastal spaces will enlarge allowing the air to enter into the lungs.

In the lungs, oxygen that is present in the inhaled air diffuses into the capillaries of the alveoli. This oxygen combines with the haemoglobin of the red blood cells and forms oxyhaemoglobin. Carbondioxide present in the blood diffuses out into the alveoli.

2. Expiration:

The muscles of the chest cavity and the diaphragm return to their normal position and results in the decreased size of the expanded chest cavity. The expanded lungs get back to their normal size as the lungs are elastic in nature. The air gets expelled in the same way as it entered the lungs, along with the carbondioxide.

During the process of expiration, the inspiratory muscles relax, the muscles of the abdomen, ribs and sternum lowers and the chest cavity contracts, this causes the increase of pressure in the lungs and the air gets expelled out.

The atmospheric air that enters the lungs contain 79% of nitrogen, 21% of oxygen and 0.03% of carbondioxide. The air that is exhaled from the lungs contains 79% of nitrogen, 16% of oxygen and 4.4% of carbondioxide. Water vapour will also be sent out along with the exhaled air.

Tissue Respiration

Tissue respiration is also known as internal respiration. When the blood enters the tissues, oxygen present in the oxyhaemoglobin diffuses into the tissues. Carbondioxide from the tissues diffuse out into the blood. The blood containing carbondioxide is taken to the lungs for exhalation.

A human being normally breathes 18 times per minute. He consumes 1.5 litres of oxygen per minute.

Breathing rate increases while performing the activities like running and jumping. The lungs are capable of taking higher amount of oxygen depending on the requirement. Health can be improved by doing breathing exercises.

  organ systems, Respiratory System