Most of the cell types in your body appear in many places — for example, humans have photoreceptors throughout our nervous systems, not just our eyes. So it seems strange that taste receptors would only be found on the tongue.
Turns out, you actually have taste receptors throughout your body; you just can't taste what they're tasting, said Nirupa Chaudhari, a professor of physiology and biophysics at the Miller School of Medicine at the University of Miami.
However, the mouth is the only place you'll find taste buds, which require two things: a cluster of cells and nerves that connect it to the region of the brain that perceives taste, Chaudhari told Live Science.
Related: Why does eating pineapple make your mouth tingle?
Taste buds are clusters of taste receptors that detect the nutrients in food and send messages about them to the gustatory cortex — the taste center of the brain. That lets you perceive taste.
Taste receptors in many of your organs also detect nutrients; but they exist on their own and don't connect to the brain's taste center.
But if we can't taste what they're tasting, why call it "taste" at all?
"The answer is very simple," said George Kyriazis, an assistant professor of biological chemistry and pharmacology at The Ohio State University College of Medicine. "The person that discovers a new molecule with a new function gets to name that molecule. And of course, the people that discovered this discovered it first on the tongue. That's why they coined 'taste receptor.'"
But taste receptors were eventually found far beyond the tongue. Scientists knew that the cells lining the gut were detecting certain chemicals to regulate digestion, so they went looking for the specific cells responsible — and found the same taste receptors we have on our tongues.
The tongue and the gut are both a part of the digestive system, and these cells were both found in the epithelium, or the layers of cells that line the organs, so this wasn't too surprising. But then researchers started venturing further.
For example, Kyriazis' lab discovered sweet taste receptors in the beta cells of the pancreas, where they help to regulate insulin.
Again, not necessarily groundbreaking: the tongue, the gut and the pancreas are full of cells that secrete something in response to chemical signals. Other discoveries followed this theme.
"Over the first 15 years, several labs around the world described functions of taste receptors that are more related to epithelial or secretory cells," Kyriazis told Live Science. "Now things have moved on."
He and others have since found taste receptors in places you might never expect: body fat, heart muscle, skeletal muscle, the bladder and even the brain, "which indicates that they are broader nutrient sensors and they are not confined within one cell type or one specific function," Kyriazis said.
As another example, taste receptors have been found in the trachea and bronchi, where they play a role in our innate immunity, Chaudhari pointed out. In mice, bitter taste receptors in the airways have also been linked to breathing regulation.
Bitter and umami taste receptors have even been found in the testes. When scientists knocked out bitter taste receptors in the testes of mice, it led to a reduction in sperm volume.
Given that we're only just beginning to understand how widespread taste receptors are in the human body — and all of their diverse functions — it's possible that they could be the answer to some previously frustrating questions.
Perhaps, Chaudhari suggested, artificial sweeteners aren't as effective for weight loss as we once thought because taste receptors in our guts are reacting to it as if it's sugar. We don't know if that's the case, but we do know that taste receptors in the gut detect artificial sweeteners, she said.
"By definition, if you have an artificial sweetener that, by one way or another, increases in the blood, that can have an effect in targeting taste receptors," Kyrazis said. "But I'm not convinced that this is very well described … we need more research on that."
