Mechanism of breathing | Inhalation & Exhalation | 

Breathing
1. Inhalation is the process of intake of air into lungs, whereas exhalation is the process of letting air out from lungs.
2. Inhalation is an active process, though exhalation is a passive process.
3. The diaphragm contract during the inhalation and get flattens by moving down, while they relax during exhalation and turned into dome-shaped by moving up.
4. The intercostal muscles relax and external costal muscles contract in the inhalation process, while in the exhalation process internal intercostal muscles contract and external intercostal muscles relax.
5. The volume of lungs increase during inhalation it means it gets inflated and it decreases during exhalation means it gets deflated.
6. The size of chest cavity increase in inhalation and it decrease during exhalation.
7. During the inhalation air rich in oxygen is taken into the blood but carbon dioxide is pushed out in exhalation process from the blood.
8. Due to the effect of intercostal muscles rib cage moves upward and outward in inhalation, while in exhalation the rib cage moves downward.
9. The composition of air which is inhaled is oxygen and nitrogen mix, while the composition of air which is exhaled is carbon dioxide and nitrogen mix.
10. Inhalation results in a decrease in air pressure (below atmospheric pressure). In exhalation, there is an increase in air pressure.
Protection of the Lung
Each lung is surrounded by an invaginated sac. The layer of tissue that covers the lung and dips into spaces is called the visceral pleura. A second layer of parietal pleura lines the interior of the thorax. The space between these layers, the intrapleural space, contains a small amount of fluid that protects the tissue by reducing the friction generated from rubbing the tissue layers together as the lungs contract and relax. If these layers of tissues become inflamed, this is categorized as pleurisy: a painful inflammation that increases the pressure within the thoracic cavity, reducing the volume of the lung.
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