A lung receptor is a specialized structure in the lung involved in the control of breathing. Lung receptor function varies because there are a number of different types, but all are connected to nerves and alter breathing in various ways. Pulmonary stretch receptors are triggered when the lungs are inflated past a certain point, when they cause the breathing rate to slow. Irritant receptors respond to cold, and substances such as smoke and dust, causing airway narrowing and coughing. J receptors cause shallow, rapid breathing in response to lung congestion, which can be caused by conditions such as heart disease.
The pulmonary stretch receptor is thought to be located in muscle inside the walls of the airways, or bronchi. This type of lung receptor is described as slowly adapting because it keeps on responding to continued stimulation. Its response is triggered by lung inflation and it causes an increase in the time spent breathing out, leading to an overall slowing in the rate of respiration.
This effect is known as a Hering-Breuer inflation reflex, and it only occurs in adults when the lungs are unusually inflated, as happens during exercise. There is also a deflation reflex, where lung deflation leads to a decrease in the time spent breathing out, resulting in an increased respiration rate. It is thought that this reflex might be important in helping babies breathe immediately after birth.
The location of irritant receptors is thought to be in between the cells that line the air sacs, or alveoli, of the lungs. This type of pulmonary receptor causes over-breathing, coughing, narrowing of the airways and mucus production. These kinds of changes are seen in the disease known as asthma. The irritant receptor is known as a rapidly adapting lung receptor because it does not carry on responding to continued stimulation.
J receptors are thought to lie in the walls of the alveoli, close to blood vessels. This type of respiratory tract receptor got its name because it is located near small blood vessels known as capillaries. The letter J is short for juxtacapillary, which is Latin for near the capillary.
Researchers have found that this type of lung receptor responds to certain chemicals and to overinflation of the lungs. In life, stimulation of the J receptor is thought to occur when fluid builds up in the alveoli, or when the capillaries become abnormally full of blood. Heart failure or a blood clot in the lungs could lead to such conditions. Stimulation of the J receptors causes rapid breathing, narrowing of the bronchi and mucus production.