Mucociliary clearance in health and disease
Pulmonary defence mechanisms
Several pulmonary defence mechanisms are found in the upper respiratory tract. The first are the presence of thick hairs or nasal vibrissae that grow inside the nostril, preventing larger particles from entering the nasal passages. Sneezing is initiated in response to irritating substances, removing the particles from the nasal passages under considerable force. A sneeze can propel up too 40,000 droplets through the air at 95 mph up to a distance of 15 feet.
Inside the nose itself are three long, narrow 'shelves' of bone known as the nasal turbinates. The turbinates are lined with tiny hairs, or cilia, that further filter, heat and humidify the inspired air. This prevents excessive drying of the mucous membranes during variations in atmospheric temperatures and humidity.
Due to the anatomy and functions of the nasal passage it is preferential for patients to inspire through their nose.
List some conditions, in the box below, under which patients may be unable to breathe through their nose and consider why (your answers will not be recorded).
Further down the upper airway is the epiglottis. This consists of a flap of elastic cartilage, attached to the base of the tongue. During swallowing the larynx rises and the epiglottis folds downwards, guarding and covering the entrance to the trachea. This protects the lungs from the aspiration of saliva, food and drink.
Once the inspired air passes into the trachea it enters the relatively sterile environment of the lungs and lower respiratory tract. The airway walls themselves are lined with cilia and mucous which protect the lungs from any particles that have escaped filtration from the upper airway. This highly effective system is known as the mucociliary escalator and is responsible for protecting the lower respiratory tract from infection and inflammation.
