Appliance of science: Why does your stomach rumble?

Some say it’s a sign of hunger or an upset stomach, but regardless of what causes it, we are all familiar with the odd sounds our stomachs can make, writes Dr Naomi Lavelle.

Appliance of science: Why does your stomach rumble?

Some say it’s a sign of hunger or an upset stomach, but regardless of what causes it, we are all familiar with the odd sounds our stomachs can make, anything from a low rumble to a full on growl.

These sounds are perfectly natural though and are just a sign that our bodies are working correctly; but why does our tummy make the noise at all?

A big name for a little rumble

The simple sounds of our stomach have quite and elaborate name; these gurgling and rumbling noises are referred to as borborymi. This onomatopoeic word was first coined by the ancient Greeks and quite simply translates as rumbling.

Where does the noise come from?

Those rumbling noises we hear come from our digestive system, which stretches from the mouth to the anus can come from the stomach or the small intestine.

Squeezing a tube

The noises are created as food, and other content, move down through the digestive system. Much of the digestive system is like a muscular tube and to pass food along the muscles must move in a certain way.

First a small area of muscles contract, like squeezing a ring around the tube, and this pushes the food and other content a little further along. Then those muscles relax and the muscles in front of them contract and so on, pushing food, liquids and gases down along the system with each contraction.

This muscular movement is called peristalsis. The noises are created by the process of peristalsis.

Is it only when stomachs are empty?

Although we associate the sounds with an empty stomach they can actually occur at any time. They do however tend to sound louder when our stomach and intestines are empty and there is no content to absorb and muffle the noise. We are therefore more aware of these rumbling, growling and gurgling sounds when they are at their loudest.

Not just when we eat

So if these sounds are connected with peristalsis why do we also hear them when there is no food in our stomachs?

That is down to something called the Migrating Motor Complex, (MMC), a specific type of electrical pulse that triggers peristalsis in the digestive system.

This is thought to serve a house-keeping function, clearing out any leftover food particles, mucus, bacteria or other debris from the stomach and small intestine.

Rumbling times

The MMC response is triggered every 90 to 120 minutes, until the next meal is eaten. It does tend to quieten down a bit while we sleep and then ramps up the activity again when we waken, which is why we often have gurgling tummies in the morning, and why we associate the sound with hunger.

The MMC cycle is broken once we eat food, so that is one of the ways to stop those gurgling noises.

A sign of good health

Although some might find the rumbling noises of our stomach and small intestine a little embarrassing, they are a sign of a healthy system. People with a sluggish digestive system and an ineffective MMC might not make as much noise from their stomachs but they can suffer with health issues such as indigestion, abdominal pain and feelings of nausea.

So next time your tummy rumbles, you can take it as a good sign.

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