The three main receptors plays a vital role in the cough:
- Rapidly adapting receptors (RARs) that respond to mechanical stimuli, cigarette smoke, ammonia, acidic and alkaline solutions, hypotonic and hypertonic saline, pulmonary congestion, atelectasis, and bronchoconstriction
- Slowly adapting receptors (SARs)
- Nociceptors on C-fibers that respond to chemical stimuli as well as inflammatory and immunological mediators such as histamine, bradykinin, prostaglandins, substance P, capsaicin, and acidic pH
It is believed that the cough is caused by the following mechanism due to hypersensitivity reactions:
Cough is described as an chronic infection which shows inflammation in the pulmonary airway and
bronchial hyperresponsiveness to an allergen. Inflammatory cells are
accumulated in respiratory bronchioles.
Physiologically, allergen inhaled results in provocation of the inflammatory system of the respiratory
system resulting in increased secreation of inflammatory mediators such as methacalmine and
histamine. Release of histamine from the mast cells results in activation of the prostaglandins and
leukotrienes.In addition to that cytokines are also released from the mast cells which leads to
Increased vascular permeability, mucus secretion, bronchospasm, and wheezing. These leads to the bronchoconstriction and the airway is disturbed which results in cough mechanisms.
Triggering factors that results in blockage of the pulmonary airway include cold air, exercise, viral upper
respiratory infection, cigarette smoke, and respiratory allergens. Bronchial provocation with allergen
induces a prompt early phase immunoglobulin E (IgE)-mediated decrease in bronchial airflow. Initially
there is an increase in the leukocyte count in the pulmonary ares with help of CD4+ cells. The activated
T-lymphocytes also direct the release of inflammatory mediators from eosinophils, mast cells, and
lymphocytes. The cross-linkage of two IgE molecules by allergen causes mast cells to degranulate,
releasing histamine, leukotrienes, and other mediators that perpetuate the airway inflammation.
Histolopathology of the bronchial airway might shows an inflammatory infiltrate consisting
of eosinophils , mast cells, lymphocytes, monocytes, and neutrophils.