So what exactly happens in the stomach?
First of all, the stomach is a small part of the whole digestive system. So much occurs elsewhere, right from lips, mouth, tongue, throat, oesophagus, through the stomach to the small intestine – where the pancreas and liver help out by squirting stuff in to help break down nutrients – then down to the large intestine and finally through the rectum (which in itself is a whole riveting story that I’ll tell you another time!)
But the stomach then…
Food takes about four seconds to get from mouth to stomach, liquid takes only one second. They go down your food pipe (oesophagus) and pass through a ring called the cardiac sphincter that sits between the oesophagus and the stomach; a sphincter is a ring of muscle that opens and closes to let stuff through or keep it out. When this sphincter is a bit dodge it can let stomach acid flow upwards into the oesophagus, then you get heartburn. Alcohol is one cause of this as it relaxes the sphincter (ooh er missus).
The top part of your stomach is kind of a holding place where food can sit for an hour while any starch is worked on by enzymes. Once the food goes into the main bit of the stomach (called ‘the body’) it mixes with strong acid (just a tad less acidic than battery acid!) and digestive enzymes which start to break it down like crazy.
Squash and squeeze
The stomach has three layers of muscle, the fibres of one layer run horizontally, another layer’s fibres run vertically and a third’s run diagonally. This means the stomach can squash and squeeze this way and that to crush food. How awesome is that?!
The stomach doesn’t digest itself because its inside is coated in a really thick layer of mucous. When someone gets a stomach ulcer a bit of that mucous has ‘gone missing’ which means stomach acid can attack the cells of the stomach lining. That can happen when someone gets an infection such as H-Pylori.
When your stomach is empty it’s kind of long and hollow like a big sausage. On its inside it has loads of folds which means it can stretch to accommodate about 2L of food (not recommended), plus the folds increase its surface area. As it fills up it becomes pear shaped.
Fast and slow food
Food can stay in the stomach for several hours if it’s difficult to break down – this is normally if you eat very fatty food. The stomach will keep churning it around and around, up and down, side to side until the whole lot is the consistency of pea soup. At this stage the pea-soupy contents are called ‘chyme’ (pronounced kyme).
Some foods pass through really fast, such as refined carbs – cake, white bread, biscuits, breakfast cereals, sweets and so on, essentially because their cells have already been broken down during manufacture by humans, so the stomach hardly has a thing to do. That’s why they don’t keep you full and you can fit more of them in, and why snacking is a habit you should try to kick.
Imagine putting a piece of broccoli in a container of acid and a doughnut in another container of acid – which would disappear first? Yep, the doughnut because its ingredients have been bashed and crashed to small particles (refined).
Same idea applies to the stomach. Protein, fatty foods and vegetables will take longer; for instance the chains of protein molecules in Greek yoghurt will need working on by stomach enzymes as well as enzymes in the small intestine, to break them apart into individual amino acids. Add some nuts, seeds and fruit and the stomach has a bit of a job on. Hello feeling full for longer!
Does the stomach actually ‘digest’ things though?
Not as such. Hardly anything is absorbed through the stomach apart from a bit of alcohol, aspirin and some anti-inflammatory drugs. Absorption of nutrients happens in the small intestine.
So once the pea soup ‘chyme’ is ready to move into the small intestine another sphincter, this time at the bottom of the stomach, between the stomach and small intestine, opens, it’s called the pyloric sphincter. But it doesn’t just open and stay open, it opens and closes so the chyme is squirted through periodically. When the top bit of the small intestine fills with chyme it signals to the sphincter to close. When the chyme has moved down a bit the sphincter opens again and more chyme is sent down from above. Like I’ve said before, the small intestine is a stickler for housework so it’s pretty controlling over the opening and closing of the pyloric sphincter.