Smell Receptors in Places That Are Not the Nose — Why Does the Body Hold So Many of Them?

Today I want to tell a story that is still in progress. Not a story that has been settled, but a place being actively dug into right now.

It starts from something odd

Counting up human genes, something odd was found.

The smell genes are unusually many. How many — when human genes are sorted into families, the largest family is the olfactory receptor genes. The functioning ones alone come to about 400. And that is so even though humans are not animals that live as dependent on smell as dogs or mice.

Does smelling really need all that.

That question was the starting point.

But they turned up outside the nose

The more it was looked into, the more oddities came with it.

The genes were not only in olfactory cells. They are in the epithelial cells of the skin, in nerve cells, turning up all over the body. Places a long way from the nose.

Receptors sitting there are hardly going to be smelling anything. Nor is a smell going to reach a cell far from the nose.

So what are they doing.

The view shifts

Here the thinking moves like this.

Smell receptors may not be there in order to convey smell. Smell may be one use among them, and the original job something else — a switch that notices a molecule has arrived and turns on the work inside the cell.

In the nose, that switch carries on into the sensation we call "smell." But in the skin or the gut or a nerve there is no reason for it to carry on into smell. It will carry on into something else.

Seeing a receptor not as a part in a sense organ but as a switch scattered through the whole body. Research is active in this direction at the moment.

Why this is a concern of mine

I set this story alongside another axis.

Something drawing attention at the same time is a channel called Piezo. Pressing force and pulling force — pressure and tension open this channel, and that becomes an electrical signal or starts a chemical reaction inside the cell. It is the place where a physical force is translated into the cell's language.

The two are telling the same story.

The body has switches that turn what came from outside into work inside the cell, and those switches are far more numerous, and in far more places, than we had known. Some notice a molecule; some notice a force.

And those switches mostly begin their work by moving ions. (A Signal That Turns Up Everywhere — On Ions)

What this has to do with herbal medicine

Here is why I keep an interest in this story.

Herbal medicine is a medicine with tens, hundreds of compounds in it. Asked what those compounds do in the body, the answer up to now has mostly run along the lines of "it presses on such-and-such a receptor." But if that list of receptors is far longer than we had known, then there are far more places to put the question to.

Why so many aromatic herbs are used. What that aroma is, is molecules going to the nose. But if the receptors that notice those molecules are not only in the nose — the question changes. (Some Medicines Are Felt the Moment You Take Them)

Why treatment that works with pressure changes the body. That the force of a hand pushing moves tissue physically, we know that much. But if that force is also pressing on a cell's switch, a further layer to the story appears. (Chuna That Does Not Crack Bones)

Far more is still unknown

That the smell genes are many, and that the receptors turn up outside the nose as well — this much is confirmed.

What each of those receptors does is being worked out one at a time, and most of it is still unknown. Which herbal compound touches which of them is less known still.

So I do not use this story as an answer. I do not say "herbal medicine works by pressing on these receptors." There are no grounds for saying that.

I do, though, watch this direction with interest. The picture by which we understand the body is widening, and the things I have long worked with sit in the space it has widened into.

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Why does the body hold so many smell genes. A question that started from something odd is becoming, now, a story about switches throughout the whole body.

I will not pretend to know the answer. But that such a question is open at all means there is much about the body we still do not know. And I like that open space.

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References

• That olfactory receptor genes are the largest family among human genes — press release, 2004 Nobel Prize in Physiology or Medicine — Nobel Committee
• That pressing force opens ion channels directly — press release, 2021 Nobel Prize in Physiology or Medicine — Nobel Committee
• A study confirming that olfactory receptors are expressed across tissues throughout the human body — PLoS ONE, 2013

Written by Dr. Heo Ji-young (PhD in Korean Medicine Pathology, Kyung Hee University · former Research Professor of Herbology, Kyung Hee University)