The respiratory system supplies the body with a constant supply of oxygen. Knowledge and understanding of the respiratory system is necessary for effective resuscitation.
The respiratory system consists of upper and lower airways.
Upper airways
The upper airways include the nostrils, nasal cavity, mouth, pharynx (throat) and larynx (voice box).
The throat is a common passageway for food and air. It starts from the cavity at the back of the mouth and nose then continues to the separate trachea and oesophagus.
The upper respiratory tract is the most common location for an airway obstruction.
Lower airways
The lower airways include the trachea and lungs, which consist of bronchi, bronchioles and alveoli.
The trachea (windpipe), allows air to pass to and from the lungs. It is in the front of the throat and begins at the larynx and vocal cords, extending down to the lungs. The oesophagus is behind the trachea and carries food and liquids to the stomach (or back from the stomach to the throat during vomiting or regurgitation).
The trachea divides into two bronchi known as the left main bronchus and right main bronchus, which then divide into progressively smaller bronchioles and, finally, alveoli (air sacs), which are surrounded by capillaries.
The tubular trachea and bronchi are kept open by C-shaped rings of strong connective tissue (cartilage), making them semi-rigid tubes (rather like vacuum tubing used to clean out swimming pools). These rings hold the trachea and bronchi open, allowing airflow to and from the lungs.
The lungs are located on either side of the chest (thorax) and fill most of the chest cavity, which is separated from the abdomen by a large sheet of muscle known as the diaphragm.
How do we breathe?
Breathing is the act of moving air into and out of the lungs.
Breathing in is called inhalation. It is an involuntary muscular action caused by contraction of the muscles to lift and expand the chest while the diaphragm is pulled down and flattened. This combined action increases the size of the chest cavity and draws air into the lungs.
Breathing out is called exhalation. Exhalation is caused when the muscles of the chest and the diaphragm relax. As the chest cavity becomes smaller, air is pushed out of the lungs.
The air we breathe in contains 21 per cent oxygen. Some oxygen in the air is absorbed by the lungs into the bloodstream and the air we breathe out contains 16 per cent oxygen.