Main Parts of the Human Respiratory System

The following is a summary of the main components of the respiratory rystem.




The Nose

The technical medical term for ‘nose’ is ‘nares’.

It contains ciliated cells and goblet cells (see below).

Note about Smoking:
Smoke paralyses the cilia and continued smoking destroys the cilia / ciliated cells, which are then replaced by goblet cells. This causes the accumulation of excess mucus in the lungs together with particles, tar, and carcinogens.

  1. Moistens air
  2. Filters air
  3. Warms air
  4. Senses/detects odours
  5. The goblet cells of the nares produce mucus
  6. The cilia 'waft' particles away from the lungs (towards the oesphagus).


Known colloquially as the ‘Voice Box’, the larynx contains vocal cords that vibrate when sound is made.

The vocal cords are also known as the ‘vocal folds’.

Forming the sounds that comprise speech.


The Naso-Pharynx is the junction of the nasal passage and the buccal cavity (i.e. the mouth).

A muscular tube lined with mucous membrane, that extends from the beginning of the oesophagus (gullet) up to the base of the skull.

It is divided into the:

  • Nasopharynx
  • Oropharynx
  • Laryngopharynx

The pharynx acts as a passageway for food from the mouth to the oesophagus, and as an air passage from the nasal cavity and mouth to the larynx. It also acts as a resonating chamber for the sounds produced in the larynx.


The windpipe, the part of the air-passage between the larynx and the main bronchi (i.e. from just below the Adam’s Apple, passing behind the notch of the sternum). This is kept open by a ‘C’-shaped ring of cartilage, the hyoid bone.

The upper part of the trachea lies just below the skin, except where the thyroid gland is wrapped around it.

The lower part of the trachea divides into two bronchi (one for each lung). These lead to the upper and lower bronchioles, and eventually the alveolar ducts.

Connects the external respiratory organs (nares and buccal cavities) with the lungs.


The bronchi are air passages beyond the trachea, which have cartilage and mucus glands in their walls.

The trachea divides into two main bronchci, which divide successively into five lobar bronchi, 20 segmental bronchi, and two or three further divisions

Components essential for external respiration.


Bronchioles are subdivisions of the bronchial tree that do not contain cartilage or mucus glands in their walls.

They (bronchioles) open from the 5th or 6th generation of bronchi and extend for up to 20 more generations before reaching the terminal bronchioles. Each terminal bronchiole divides into a number of respiratory bronchioles, from which the aveoli open.

Components essential for external respiration.

Each terminal bronchiole conducts air to an acinus in the lung.


The covering of the lungs.

The covering consists of serous membrane, which has a smooth shiny moist surface due to the secretion of small amounts of fluid. This fluid lubricates the opposing visceral and parietal surfaces so that they can slide painlessly over each other during breathing.


The covering of the lungs.


The covering of the inner surface of the chest wall.


The pleural cavity is the space between the visceral and parietal pleura, which is normally very small as the pleural membranes are in close contact. The introduction of fluid (pleural effusion) or gas separates the pleural surfaces and increases the volume of pleural space.



An alveolus in the lung is a blind-ended air sac of microscopic size.

About 30 alveoli open out of each alveolar duct, which leads from a respiratory bronchiole. The alveolar walls, which separate alveoli contain capillaries. The alveoli are lined by a single layer of pneumocytes, which thus form a very thin layer between air and blood so that exchange of oxygen and carbon dioxide is normally rapid and complete.

Children are born with about 200 million alveoli.

The adult number of about 300 million is reached around the age of eight years.

Components essential for external respiration.


The diaphragm is a thin musculomembranous dome-shaped muscle that separates the thoracic and abdominal cavities.

It is attached to the lower ribs at each side, and to the breast bone and the backbone at the front and back.

It bulges upwards against the heart and lungs, arching over the stomach, liver, and spleen.

There are openings in the diaphragm through which the oesophagus, blood vessels, and nerves pass.

The diaphragm plays an important part in breathing. It contracts with each inspiration, becoming flattened downwards and increasing the volume of the thoracic cavity. With each expiration the diaphragm relaxes and is restored to its dome shape.

See also information about other aspects of the respiratory system, such as pulmonary circulation.

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