It turns out that the nose is not the only organ capable of sensing and distinguishing odors. But rather than perceiving them as the sense of smell, our lungs react to the presence of noxious chemicals by triggering an automatic response: a cough.
We know that we have taste receptors in our lungs, but the discovery of a class of cells that express olfactory receptors in human airways, called pulmonary neuroendocrine cells, or PNECs, is completely new. Researchers at Washington University in St. Louis and the University of Iowa discovered the receptors in the membranes of neuroendocrine cells. These specialized cells send nerve impulses to the brain allowing it to "smell" chemicals contained in potentially hazardous inhaled stimuli, like perfumes, cigarette smoke, industrial solvents, and others. Once an acrid odor has been sensed, it triggers the chemosensory cells to dump hormones that make the airways constrict. In other words, we cough.
"We forget that our body plan is a tube within a tube, so our lungs and our gut are open to the external environment," said lead researcher Yehuda Ben-Sharar in a statement. "Although they're inside us, they're actually part of our external layer. So they constantly suffer environmental insults and it makes sense that we evolved mechanisms to protect ourselves."
Put another way, the PNECs are guards whose job it is to exclude irritating or toxic chemicals.
"They are possibly designed to elicit a rapid, physiological response if you inhale something that is bad for you," said Ben-Sharar.
So unlike the unpleasant smell of noxious chemicals through our nose — which is something we could conceivably get accustomed to — certain chemicals trigger a response that's quick and largely automatic.
Read the entire study at ATS Journals: "Volatile-Sensing Functions for Pulmonary Neuroendocrine Cells."
Images: Ioannis Pantzi/Shutterstock/Ben-Shahar.