What Causes Coughing?
Micro-organisms and Atmospheric Pollutants are the Chief Culprits
May 26, 2009
Coughing is a natural reflex that everyone has experienced. It's designed to remove irritation and micro-organisms from the lungs and upper respiratory tract: the trachea and bronchi and thereby prevent damage and infection.
Like some (probably most) of the body's defense systems, the coughing action which can be so unpleasant or even life-threatening, is essential for health in the long run.
Cough Mechanism
The lining of the respiratory tract contains cells which produce sticky mucus (sputum) to trap particles of chemicals and micro-organisms and prevent them entering the lungs. Other cells in the tract have hairs called cilia. These 'beat' in a particular direction, away from the lungs and up towards the mouth. In this way anything caught in the mucus is moved towards the mouth and can then be swallowed or spat out.
The respiratory tract lining also contains receptor cells. These are sensitive to accumulations of irritants, micro-organisms and mucus. Such a build up sends a signal to the brain's cough centre which triggers the muscular action of coughing
Mostly this works well but occasionally the receptor cells become too sensitive, perhaps as a result of a viral infection or maybe due to an allergic process as in asthma. The cells then trigger a coughing reflex even when the irritation is minimal. Such things as pollen or even walking from a warm to a cold environment can provoke coughing.
Disease of The Lung and Upper Respiratory Tract
Coughing is usually due to infection or damage to the respiratory organs. This is mostly relatively trivial resulting from a cold or flu virus although such infections can predispose to more severe bacterial infections and/or pneumonia and sometimes lasting damage to the lung tissues.
Diagnosis of respiratory disease is made from the history: when does the coughing occur? What sort of cough is it? Are there any other symptoms? Chest X rays may be taken to look for signs of damage or infection. And the sputum is examined for quantity, viscosity,colour and the presence of blood
Major Causes of Coughing
Very many conditions can cause coughing – usually any one of a variety of micro-organisms and industrial pollutants entering the bronchial tree. Disease involving the the blood supply to the lungs or to the surrounding tissue; for example pleurisy can also produce coughing.
- Viral infections: usually colds and flu. Normally not serious and self-limiting.
- Acute bronchitis: bacterial infection of the bronchial tree. May cause the production of thick, yellow or green sputum. Usually associated with fever and malaise. Can be more of a problem if associated with antibiotic resistant bacteria like MRSA.
- Chronic Bronchitis: co-exists with emphysema. It is a chronic inflammatory process within the respiratory tract. Associated with much mucus production. Such patients are very prone to chest infections. Causative factors are atmospheric pollution, especially cigarette smoke.
- Asthma: due to allergic reaction which constricts airways and causes wheezing and coughing. Usually well-managed these days but potentially serious. Can be triggered by all sorts of allergens such as cigarette smoke, perfumes and stress.
- Pneumonia: can be caused by viruses or bacteria and may follow some milder chest infection. The lung tissue itself is affected leading to much inflammation and build up of fluid in the lungs. Associated with fever. Aspiration pneumonia is caused by inhaling micro-organisms from the mouth or nose more often than not from vomit.
- Drugs; some types of medication can cause a dry irritant cough. ACE inhibitor drugs used to control blood pressure are an example.
- Tumours: any tumour situated in or near the respiratory tract can cause enough irritation to provoke the coughing reflex. Carcinoma of the bronchus is one such.
This article is for information only. If you have any health concerns you should consult your doctor.
Resources
Essential Medicine Eds. Read and Vann Jones. Pub. Churchill Livingstone 1996
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