Question

What ¡s the normal percentage composition of gases in inspired air and expired air
respectively?

Answer 1

Hint: Inspiration or inhalation and expiration or exhalation of air is an essential step in the breathing process. It is also called ‘external respiration’ as it is an external process of taking the air is inhaled and carbon dioxide is exhaled through respiratory organs.

Step by step answer:The process of breathing involves contraction and relaxation of several intercostal muscles present in the thoracic cavity because the lungs are not capable of inflating on their own. In humans, inflation of the lungs takes place by the contraction of the diaphragm and the intercostal muscles, causing the rib cage to rise upwards and outwards.
During inhalation, the air is taken in through the nose that passes through the nasal passage, the
pharynx, the larynx to reach the trachea that is divided into several narrower branches bronchi. Each
bronchus is further divided into narrower bronchioles. The bronchioles end into air sacs called alveoli.
The composition of inhaled air is Oxygen is 20.93%, carbon dioxide is 0.04% and nitrogen is 78.08%.
The exchange of gases takes place in the alveoli where the oxygen is diffused into the blood present in
the blood vessels, and the carbon dioxide from the blood is diffused into the alveoli. From Alveoli carbon
dioxide is exhaled out. Exhalation is a passive process because the diaphragm and other respiratory
intercostal muscles relax, causing the lungs to contract.
The composition of expired air is Oxygen is 16.23%, carbon dioxide is 4.4% and nitrogen is 78.08%.
The air in the lungs then gets pushed up and out, which causes it to pass through the trachea and nasal
passage back to the atmosphere.

Note: Inhaled air is by volume 78.08% nitrogen, 20.95% oxygen and carbon dioxide is 0.04%. The gas exhaled contains carbon dioxide is 4% to 5% by volume. It is about a 100 fold increase over the inhaled amount.