Describe the structure of Human respiratory system

Human respiratory system consists of a pair of external nostrils, nasal cavity chamber, nasopharynx, larynx, trachea, bronchioles and alveoli.

- The external nostrils present just above the upper lip lead into the nasal chamber through the nasal passage.

- The nasal chamber opens into nasopharynx, which is a portion of pharynx, the common passage for food and air.

- Larynx is a cartilaginous box like structure that helps in sound production; it leads into the trachea.

- Trachea is a straight tube extending up to the mid-thoracic cavity, which divides

at the level of 5th thoracic vertebra into a right and left primary bronchi.

- Each bronchi undergoes repeated divisions to form the secondary and tertiary bronchi and bronchioles ending up in very thin terminal bronchioles.

- The tracheae, primary, secondary and tertiary bronchi, and initial bronchioles are supported by incomplete cartilaginous rings.

- Each terminal bronchiole gives rise to a number of very thin, irregular walled and vascularised bag-like structures called alveoli.

- The branching network of bronchi, bronchioles and alveoli constitutes the lungs.

- The lungs are located in the thoracic chamber which are covered by a double layered membrane called pleura, with pleural fluid between them.

- The outer pleural membrane is in close association with the thoracic cavity whereas the inner pleural membrane is in contact with the lung surface.