HSEB Notes on Respiratory Organs and Mechanisms of Breathing
Lesson : Respiration
Class : 12
Respiratory organs
There is a pair of spongy conical hollow bags enclosed in pleural cavities called lungs. The plural cavities are lined by tough, flexible and transparent membranes called pleura. The plura is double walled. The outer membrane is parietal and inner membrane is visceral membrane. These membranes protect lungs and stop leaking of air into thoracic cavity. The fluid secreted by pleura reduces the friction during breathing movement. The lungs are capable of great
expansion. They are inflated when filled with air. These are found in either side of heart. The right lung has three lobes and left lung has two lobes. The three lobes of right lung are right superior, right inferior and middle lobe. The two lobes of left lung are left superior and left inferior. The left lung has cardiac notch at its anteromedian border to accommodate the heart. There are about 750 millions of alveoli. These large no. of alveoli provide about 100 sq meter of surface. It is about 50 times of skin surface(1.6 sq m). Alveoli are extremely thin walled and vascular structure surrounded by capillary of network. These are the site for gases exchange.
expansion. They are inflated when filled with air. These are found in either side of heart. The right lung has three lobes and left lung has two lobes. The three lobes of right lung are right superior, right inferior and middle lobe. The two lobes of left lung are left superior and left inferior. The left lung has cardiac notch at its anteromedian border to accommodate the heart. There are about 750 millions of alveoli. These large no. of alveoli provide about 100 sq meter of surface. It is about 50 times of skin surface(1.6 sq m). Alveoli are extremely thin walled and vascular structure surrounded by capillary of network. These are the site for gases exchange.
Mechanism of breathing
Breathing is simply taking in of fresh air from atmosphere and giving out of used air from lungs. Breathing renews constantly the air present in the lungs. It is accomplished through changes in the volume and air pressure of the thoracic cavity. Change in volume and air pressure is carried out by movement of ribs, internal and external intercostals muscles, diaphragm and abdominal muscles. Breathing can be divided into inhalation and exhalation.
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