A cough can be quite irritating and painful but in reality, it is an extremely useful process and one of the many ways in which the body strives to keep harmful substances out, ensuring you stay healthy. To understand more about how this is possible, it is important to first understand the structure of the respiratory system that is involved with breathing as well as phenomena such as coughing and sneezing.
Anatomy of Respiratory System
The respiratory system consists of several organs: nose, mouth, pharynx or the throat, larynx or the voice box, trachea or the wind pipe, tiny air tubes called bronchi and finally, the lungs. Of these, the nose, the sinuses around it and the larynx make up the upper respiratory tract and the trachea, bronchi and lungs make up the lower respiratory tract. [1] The linings of the bronchi are supplied by several sensory nerves that are connected to a portion of the medulla oblongata in the brain known as the ‘cough center’.
Cough Receptors
Cough receptors are present in several parts of the respiratory tract such as the trachea, bronchi, pharynx and the points where the large airways branch. These receptors respond to mechanical stimuli such as touch and movement as well as chemical stimuli such as heat, acidic substances and compounds such as capsaicin that are found in chillies. Besides, they are also present in the eardrums, sinuses, pharynx, pleura or the membranes covering the lungs and the external auditory canals. These receptors are believed to respond only to mechanical stimuli. [2]
What Happens During a Cough?
As NetDoctor UK explains, coughing is a reflex that begins when the sensory nerves in the respiratory system are stimulated due to the presence of a chemical or mechanical stimulus.[3] When the cough receptors are stimulated, an impulse travels through the nerves to the cough center in the medulla. This causes the cough center to respond by sending information to the muscles in the respiratory system to contract in such a way that it produces a cough to throw the irritant out of the body at great force along with a burst of air.[2]
Cough: The Process[4]
Vigorous Cough can be Dangerous
Have you ever noticed how continuously coughing for a few hours or days tends to give you a headache, makes you feel dizzy, causes urinary incontinence, makes you tired and causes pain in the chest and back? All these symptoms are a result of the high pressure generated when you cough very vigorously – this may be as high as 300 mm of Hg and the velocity at which air is expelled out is close to 800 kilometers per hour. [2] Now this tremendous pressure and speed of air is good in terms of the ability to clear the irritants and mucus from the respiratory passages but it also leads to complications. Some people – especially women with low bone density – have been known to suffer from rib fractures that are induced by cough.[2]
Ensuring the lower respiratory tract and the lungs always remain sterile (that is, free of microorganisms) is one of the major parts of the body’s defense systems. This, precisely, is how the cough reflex plays a protective role. In the absence of such a reflex, dirt can enter the lungs and trigger the growth of microorganisms that lead to complications such as respiratory infection and pneumonia. However, when the cough becomes chronic or excessive, it can lead to other type of complications such as damage of the inner linings of the respiratory passage and therefore, it becomes necessary to find a way to get rid of such cough.
Also read: Coughs are of different types, so are their solutions
References
1 Wexner Medical Center, Ohio State University, Anatomy of the Respiratory System
2 Mario Polverino et al, Anatomy and neuro-pathophysiology of the cough reflex arc. Multidisciplinary Respiratory Medicine 2012, 7:5 http://www.mrmjournal.com/content/7/1/5
3 Netdoctor: Coughing
http://www.netdoctor.co.uk/health_advice/facts/cough.htm
4 Washington Post: Anatomy of a Cough
http://www.washingtonpost.com/wp-srv/health/interactives/cold/