How your digestive system works

00:06 Across the whole planet, humans eat on average between one and 2.7 kilograms of food a day.

00:13 That’s over 365 kilograms a year per person, and more than 28,800 kilograms over the course of a lifetime.

00:23 And every last scrap makes its way through the digestive system.

00:27 comprised of ten organs covering nine meters, and containing over 20 specialized cell types, this is one of the most diverse and complicated systems in the human body.

00:38 Its parts continuously work in unison to fulfill a singular task:

00:42 transforming the raw materials of your food into the nutrients and energy that keep you alive.

00:48 spanning the entire length of your torso, the digestive system has four main components.

00:54 First, there’s the gastrointestinal tract, a twisting channel that transports your food and has an internal surface area of between 30 and 40 square meters, enough to cover half a badminton court.

01:08 Second, there’s the pancreas, gallbladder, and liver, a trio of organs that break down food using an array of special juices.

01:16 Third, the body’s enzymes, hormones, nerves, and blood all work together to break down food, modulate the digestive process, and deliver its final products.

01:27 Finally, there’s the mesentery, a large stretch of tissue that supports and positions all your digestive organs in the abdomen, enabling them to do their jobs.

01:37 The digestive process begins before food even hits your tongue.

01:42 anticipating a tasty morsel, glands in your mouth start to pump out saliva.

01:47 We produce about 1.5 liters of this liquid each day.

01:52 Once inside your mouth, chewing combines with the sloshing saliva to turn food into a moist lump called the bolus.

02:00 Enzymes present in the saliva break down any starch.

02:04 Then, your food finds itself at the rim of a 25-centimeter-long tube called the esophagus, down which it must plunge to reach the stomach.

02:14 Nerves in the surrounding esophageal tissue sense the bolus’s presence and trigger peristalsis, a series of defined muscular contractions.

02:23 That propels the food into the stomach, where it’s left at the mercy of the muscular stomach walls, which bound the bolus, breaking it into chunks.

02:32 Hormones, secreted by cells in the lining, trigger the release of acids and enzyme-rich juices from the stomach wall that start to dissolve the food and break down its proteins.

02:43 These hormones also alert the pancreas, liver, and gallbladder to produce digestive juices and transfer bile, a yellowish-green liquid that digests fat, in preparation for the next stage.

02:56 After three hours inside the stomach, the once shapely bolus is now a frothy liquid called chyme, and it’s ready to move into the small intestine.

03:05 The liver sends bile to the gallbladder, which secretes it into the first portion of the small intestine called the duodenum.

03:14 Here, it dissolves the fats floating in the slurry of chyme so they can be easily digested by the pancreatic and intestinal juices that have leached onto the scene.

03:24 These enzyme-rich juices break the fat molecules down into fatty acids and glycerol for easier absorption into the body.

03:33 The enzymes also carry out the final deconstruction of proteins into amino acids and carbohydrates into glucose.

03:40 This happens in the small intestine’s lower regions, the jejunum and ileum, which are coated in millions of tiny projections called villi.

03:49 These create a huge surface area to maximize molecule absorption and transference into the bloodstream.

03:56 The blood takes them on the final leg of their journey to feed the body’s organs and tissues.

04:02 But it’s not over quite yet.

04:04 Leftover fiber, water, and dead cells sloughed off during digestion make it into the large intestine, also known as the colon.

04:13 The body drains out most of the remaining fluid through the intestinal wall.

04:17 What’s left is a soft mass called stool.

04:20 The colon squeezes this byproduct into a pouch called the rectum, where nerves sense it expanding and tell the body when it’s time to expel the waste.

04:29 The byproducts of digestion exit through the anus and the food’s long journey, typically lasting between 30 and 40 hours, is finally complete.