A guide to the respiratory system

The respiratory system enables oxygen to enter the bloodstream and waste products (eg Carbon Dioxide) to be removed.

Air is drawn in through the mouth and nose, where it is warmed, filtered and moistened. The air then travels through the throat and past the epiglottis (the protective flap of skin that folds down to protect the airway when we swallow).

Air now enters the larynx (more commonly known as the voice box or ‘Adam’s apple’). It passes between the vocal cords in the larynx and down into the trachea. The trachea is protected by rings of cartilage that surrounds it to prevent kinking.

The trachea divides into two ‘bronchi’ that supply air to each lung. The bronchi then divide into smaller air passages called ‘bronchioles’. At the end of the bronchioles are microscopic air sacks called ‘alveoli’.

The walls of the alveoli are only one cell in thickness, so oxygen can pass through into the blood, which is carried in capillaries that surround the alveoli.

Carbon dioxide (a waste gas from the body) passes from the blood into the alveoli, and is then breathed out. This whole process is known as gas exchange. 

The trachea, bronchi, and lungs are contained in the ‘thoracic cavity’ in the chest.

To draw air down into the thoracic cavity, the diaphragm flattens and the chest walls move out. This increases the size of the thoracic cavity, creating a negative pressure which draws air in.

Each lung is surrounded by a two layered membrane called the pleura. Between the two layers of the pleura is a thin layer of ‘serous’ fluid, which enables the chest walls to move freely.

The thoracic cavity is protected by the ribs, which curl around from the spine and connect to the sternum(breast bone) at the front of the body.