The journey of your food
Follow one mouthful from your teeth to the far end of a nine metre tube, through acid, bile and thirty square metres of hidden lining, narrated step by step.
You take a bite
Digestion starts before you even chew. The smell of food tells your brain to get ready, and your stomach begins making acid while the first bite is still on its way down. Over a lifetime you will push about fifty tonnes of food through this tube.
Teeth crush and grind
Your thirty two teeth are a demolition crew. Incisors slice, molars grind with a force of up to seventy kilograms, and the point of all of it is surface area. The smaller the pieces, the more places your enzymes can attack.
Saliva pours in
You make about one and a half litres of saliva a day, roughly a large bottle of water. It is not just wet. It carries an enzyme called amylase that starts breaking starch into sugar, which is why plain bread turns sweet if you hold it in your mouth.
You swallow
The tongue rolls the mush into a ball called a bolus and flicks it backwards. A flap of cartilage, the epiglottis, slams over your windpipe for about half a second. You do this roughly six hundred times a day and never once decide to.
The oesophagus squeezes it down
Food does not fall down your throat, it is squeezed. Rings of muscle contract behind it in a travelling wave called peristalsis, crossing the twenty five centimetre tube in about seven seconds. That is why an astronaut can swallow upside down in orbit.
Stomach acid goes to work
The stomach is a muscular bag that churns and burns at the same time. Its juice is hydrochloric acid, about a million times more acidic than your own blood and strong enough to dissolve a razor blade in a day. Your wall survives behind a mucus coat rebuilt every few days.
The meal waits its turn
Nothing leaves here in a hurry. A meal sits for two to four hours, longer if it is fatty, while the walls knead it into a soupy grey liquid called chyme. Your stomach can stretch from the size of a fist to hold about four litres.
The pylorus lets a teaspoon through
At the exit is a ring of muscle about as wide as a pencil. It opens just enough to release a teaspoon of chyme at a time, because the delicate gut beyond it would be burned raw by a whole stomachful of acid arriving at once.
Bile and enzymes pour in
Two organs squirt in together. The pancreas adds enzymes plus a splash of alkali that neutralises the acid within seconds, and the gallbladder releases bile, a bitter green soap made by the liver that shatters fat into droplets small enough to digest.
Seven metres of small intestine
The small intestine measures about seven metres relaxed, though muscle tone holds it nearer three inside a living body. Food creeps along its coils for three to six hours, and this quiet stretch is where almost everything useful is finally pulled out of your meal.
Villi soak up the nutrients
The lining is anything but smooth. It is carpeted with millions of finger shaped villi, each one furred with even smaller hairs, folding the surface up to roughly thirty square metres. That is the floor of a studio flat, packed inside your belly.
The liver inspects everything
Every drop of blood leaving your gut goes straight to the liver first, along a private vein. The liver stores sugar, strips out poisons and decides what the rest of your body is allowed to receive. It performs over five hundred different jobs.
The large intestine reclaims water
What arrives here is mostly water and fibre. Over twelve to thirty hours the large intestine drinks that water back, while trillions of gut bacteria ferment the leftovers and pay rent by making vitamin K and several of your B vitamins.
The rest leaves, days later
From first bite to final exit takes somewhere between one and three days, yet the real chemistry is finished in the first ten hours or so. The rest is the large intestine taking its time. Every atom you are built from came in through this one long tube.
Watch it explain itself
Every step above is narrated aloud. Play it, or open it in the editor and make it yours — no account needed.