Respiration in Human beings: Notes for class 10th Biology


Following are the main structures in the human respiratory system:


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


  • It is a tube-like structure which continues after the nasal passage.


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


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


  • 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.

Alveoli: These are air-sacs at the end of bronchioles


  • It is composed of a very thin membrane and is the place where blood capillaries open.
  • This is alveolus; where oxygen mixes with the blood and carbon dioxide exits from the blood.


  • The cycle of breathing consists of two phases, i.e. inspiration and expiration.
  • Both these processes, i.e. inspiration and expiration are together referred to as respiratory movements
  • Inhalation – involves contraction of diaphragm and external intercostal muscles resulting in relaxation of rectus abdomen
  • Expiration involves contraction of abdomen and inner intercostal muscles resulting in relaxation of external intercostal muscles and diaphragm (become dome-shaped).
Mechanism of Breathing
Mechanism of Breathing
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