Breathing In, Breathing Out While breathing in, the diaphragm contracts which pulls the rib cage up and out. The space within the chest increases which reduces the air pressure inside the lungs. Then air goes through bronchi and bronchioles and at last fills up the millions of alveolus. However, while breathing out, the diaphragm relaxes and the rib cage moves down. The space within the chest decreases which increases the air pressure inside the lungs. The Respiration Process The process of respiration begins with an individual inhaling air through the nose. The inhaled air reaches the nasal cavity, which acts as a filtering unit, trapping unwanted material with the help of nasal hair. The inhaled air then flows down the larynx, pharynx, past the trachea,

which opens into the chest cavity. The trachea is divided into two bronchial tubes, which lead to the lungs.

The bronchi are further divided into very small tubes called bronchioles. Each bronchiole divides into millions of tiny sacs called alveoli. Alveoli are the part of lungs where the essential gaseous exchange takes place. They are covered with numerous tiny

Frontal sinus Sphenoid sinus Nasal cavity Nasal vestibule

Oral cavity Pharynx Epiglottis Vocal fold Trachea Cartilage

Superior lobe

Superior lobe

Carina of trachea Intermediate bronchus

Capillary beds


Branch of pulmonary artery

Main bronchi (right and left)

Pulmonary vein

Middle lobe

Inferior lobe

Inferior lobe

Respiratory bronchiole


Alveolar duct

Connective tissue




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