Anything that irritates the surface of your breathing tract between the throat and the secondary branches of the bronchial tubes can make you cough. A cough has three stages: first you draw in air; then you compress the chest; then you expel the air. In order to expel the air with force you draw up your diaphragm while your chest cavity elongates, and then by pressure of the abdominal muscles you drive the diaphragm up towards the chest like a piston.
In many common diseases cough is an outstanding symptom. In acute bronchitis one begins with a dry cough, which becomes moist as secretion develops. In this condition the chest X-ray will not usually reveal any altered condition.
In chronic bronchitis cough and expectoration, usually much worse in the morning, are the chief symptoms.
Chronic bronchiectasis has symptoms like chronic bronchitis, but the volume of sputum is large. Some patients produce as much as a quart a day. The breath and the sputum usually have an offensive odor.
Tuberculosis is associated with cough, and for this condition examination of the chest with X-ray is of utmost importance. The doctor makes a physical examination of the chest and may also send a specimen of sputum to the laboratory to search for germs of tuberculosis.
Heart failure, cancer, abscesses, embolus in the lung due to a clot that has broken loose somewhere in the circulation, and infection with parasites may be causes of cough. Some people develop a cough habit and then keep it up without any physical cause for the cough.