Class 10 Science

Life Processes: Human Respiratory System

The human respiratory system is composed of a pair of lungs. These are attached to a system of tubes which open on the outside through the nostrils. Following are the main structures in the human respiratory system:

Nostrils: There are two nostrils which converge to form a nasal passage. The inner lining of nostrils is lined by hairs and remains wet due to mucus secretion. The mucus and the hairs help in filtering dust particles out from inhaled air. Further, air is warmed up when it enters the nasal passage.

Breathing through mouth is unhealthy. Why?

Your elders may have said that you should not breathe through your mouth. Breathing through mouth is an unhealthy practice. Let us try to understand the reason behind it.

When you breathe through mouth, dust particles enter your lungs. These dust particles entering your lungs will make you sick. But when you breathe through nose, dust particles get filtered by hairs and mucus inside your nostrils. Hence, you should avoid breathing through mouth.

Pharynx: It is a tube like structure which continues after the nasal passage.

Larynx: This part comes after the pharynx. This is also called the voice box.

Trachea: This is composed of rings of cartilage. Cartilaginous rings prevent the collapse of trachea in the absence of air.

Bronchi: A pair of bronchi comes out from the trachea, with one bronchus going to each lung.

Bronchioles: A bronchus divides into branches and sub-branches, inside the lung. These are called bronchioles.


There is a pair of lungs. Lungs work like balloons. Lungs inflate like balloon when air enters the lungs.

Alveoli: There are air-sacs at the end of bronchioles. They are called avleoli. Alveolus is composed of a very thin membrane and is the place where blood capillaries open. Alveolus is the site, where oxygen mixes with the blood and carbon dioxide exits from the blood.

The exchange of gases, in alveoli, takes place due to pressure differential. The pressure of oxygen outside an alveolus is more than the pressure of oxygen inside an alveolus. Due to this, oxygen enters an alveolus.

The pressure of carbon dioxide outside an alveolus is less than that inside an alveolus. Due to this, carbon dioxide from alveolus goes out to the lung.

Breathing Mechanism

Mechanism of Inhalation Mechanism of Exhalation

The breathing mechanism of lungs is controlled by the diaphragm and the intercostalis muscles. Diaphragm is a membrane which separates the thoracic chamber from the abdominal cavity.

Inhalation: Taking in air inside the lungs is called inhalation. When diaphragm moves down, the lungs expand. Expansion of lungs creates low pressure inside the lungs and thus creates a suction force. Due to this, air is inhaled inside the lungs.

Exhalation: Giving out air outside the lungs is called exhalation. When diaphragm moves up, the lungs contract. Contraction of lungs creates high pressure inside the lungs and thus creates a pushing force. Due to this, air is exhaled outside the lungs.

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