You’re sat in your lecture, trying your best to stay awake and take some decent notes when suddenly you’re clenching your stomach muscles and trying desperately to stop the deafening sound of your stomach rumbling. The people either side of you turn and smirk as you shrink down into your seat and wonder: why is this happening?
The answer lies in the gastrointestinal (GI) tract. The GI tract is basically a tube running through the body from the mouth to the anus through which food travels and becomes digested. The walls of this contain layers of smooth muscle that contract to move food along the tube, for example from the stomach to the small intestine (think squeezing a tube of toothpaste from the bottom to move the toothpaste along the tube and out of the end). This process is called peristalsis, and is what causes the rumbling noise (called ‘borborygmus’ for anyone who’s interested). This noise is actually made even when you are full, made by the sounds of the muscles contracting. However, you can’t usually hear it because the food within the stomach and intestine muffles the sound. So, why do we associate the noise with being hungry?
This noise is actually made even when you are full, made by the sounds of the muscles contracting.
When the stomach has been empty for about two hours, receptors in the stomach wall sense this absence of food and send a message to the brain to make the muscles of the stomach and intestine start peristalsis again. Waves of electrical activity called migrating myoelectric complexes (MMCs) move through your enteric nervous system, initiating peristalsis. This is to sweep up any remaining food debris to make room for new food coming into the tract. However, as there isn’t a lot of food left lying around, the sound of the muscles contracting isn’t muffled. Add to this the sound of any gastrointestinal juices moving around and hitting the stomach wall (think shaking a half-full bottle of water compared to a full one) and you have enough of a racket going on to drown out your lecturer.
At the same time as this, the stomach lining, having detected the absence of food, produces a hormone called ghrelin. Ghrelin sends a message to the brain to say that the stomach is empty, which results in a feeling of hunger. Hence, you associate this feeling of hunger with the sound of your stomach rumbling.
When the stomach has been empty for about two hours, receptors in the stomach wall sense this absence of food and send a message to the brain to make the muscles of the stomach and intestine start peristalsis again.
So what can you do to prevent your stomach from growling at you every couple of hours? Well, dieticians recommend frequent small meals to consistently keep food in your stomach. I’d recommend a packet of mini cheddars under the desk.
Image: jeff_golden via Flickr