Organs of the respiratory system

  • Nose and nasal cavity
  • Pharynx
  • Larynx
  • Trachea
  • Two bronchi ( one bronchus to eachLungs)
  • Two lungs
  • Muscles pf breathing- intercostal muscles and diaphragm.

Nose and nasal cavity;

  • The noses is the external portion of the respiratory system and opens through the external nares or the nostrils. The nasal cavity is divided by a septum into right and left septum.
  • The nasal passages are lined by a vascular mucous membrane containing ciliated columnar epithelium due to this arrangement the air is warmed, moistened and filtered to remove the dust particles.
  • The warming is very effective inside the nose. If the air is inhaled at 6-7°C it reaches back of the nose and it is heated to 30°C the temperature of air raises to the body temperature while passing through the trachea, and the air is completely humidified and it reaches the bronch.
  • The other function of nose is olfaction or smell.

Pharynx: Both the mouth and nose opens into the pharynx it is 12-13 cm long

Pharynx is divided into 3 parts:

  • Nasopharynx: Position just superior to the nasal cavity.
  • Oropharynx: Position of pharynx posterior to the oral cavity.
  • Laryngopharynx: It is the position of the pharynx just superior to the larynx.


  • It is also referred to as voice box. Larynx extends from laryngopharynx to trachea. It forms the upper extended portion of the trachea. The larynx consists of cartilage, ligaments, membranes and muscles arranged in a way to produce voice.
  • When the food passes through the region of pharynx, a flap like cartilaginous piece is lying over the larynx helps to close the laryngeal part. This flap is called the epiglottis.

Trachea: It is also referred to as wind pipe it is 12cm long and diameter is 2.5cm. The trachea contains C shaped cartilaginous bands and is located anterior to the oesophagus. The trachea is made up of 4 layers:

  • The outermost areolar connective tissue.
  • The hyaline cartilage.
  • The sub mucosa.
  • Mucosa.

At about the 5th thoracic vertebrae the trachea divides into left and right primary bronchi.

Bronchi and bronchioles: The bronchi are formed by the bilateral bifurcation of trachea at the 5th thoracic vertebrae. The point at which trachea divides into two branches is known as carina.

  • The bronchi pass download and outwards towards the roof of the both the lungs as primary bronchi.
  • The right bronchi is shorter and wider than left one. Right bronchus is divided into upper, middle and lower secondary bronchi, whereas left bronchus is divided into upper and lower secondary bronchi.
  • The secondary bronchi further from smaller tertiary bronchi from small bronchioles. Bronchioles branch further into smaller tubes called terminal Bronchioles.


The lungs are a pair of spongy, light organs lying in the thoracic cavity. The lungs are basically rested upon the two primary bronchi. Each lung is surrounded by a delicate serous membrane called pleural membrane, the inner membrane which covers the lungs is called visceral pleural and layer which lines the wall of thoracic cavity is called parietal pleura. The space between these pleuras is called as pleural cavity filled with pleural fluid which reduces the membrane friction.

  • The right lung is divided into three lobes, superior lobe , middle lobe, inferior lobe. The left lung is divided into two lobes superior lobeand inferior lobe.
  • Each lobe of the lung is divided into small compartments called lobules , each lobule is covered by an elastic connective tissue which contain lymph vessels.
  • Inside the lobule the terminal bronchiole divides into respiratory system which further divided into alvaeolar duct. The are surrounded into alveoli and alveolar sacs.

Intercostal muscles : There are 11 pairs of intercostal muscles that occupy the space between the 12 pairs of ribs. They are two types :

  • The external intercostal muscle : These extend downward and forward.
  • The internal intercostal muscle : These extend downwards and backward.

When the intercostal muscles contract the ribs are pulled upwards ,towards the first rib which is non-moving or fixed. Due to the uplifting the rib expand the forward direction leading to expansion of chest cavity.

  • The intercostal muscles are stimulated to contract by the intercostal nerves.

Diaphragm; The diaphragm is a dome shaped muscular structure separating the thoracic and the abdominal cavity it forms the roof of thoracic cavity and roof of abdominal cavity.

  • It consists of a central tendon attached to the lower ribs and the sernum when the muscle of the diaphragm is contracted the muscle fibres shorten and the central tendon is pulled downward to the level of the 9th thoracic vertebrae enlarging the thoracic cavity.
  • the diaphragm is supplied with the phrenic nerves

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