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Seven metres of grabbing

Why Are Your Intestines So Long?

Food is only absorbed where it touches the wall, so the wall is made long, folded, and covered in fuzz.

About seven metres,coiled upFolded into ridges allalongEvery ridge covered intiny fingersEvery finger covered insmaller ones still
Four tricks, all buying the same thing: contact.

  1. Step 1 of 5

    The stomach breaks food up. It does not take it in.

    1 Churned into asoup2 Passed on alittle at atime3 Absorbed alongthe way

    Acid and churning turn a meal into a soup. Almost nothing crosses into the blood there — that work happens further down.

  2. Step 2 of 5

    Absorbing happens only at the wall.

    The tube incross-section Only the wall can takeanything in

    Broken-down food has to physically meet the lining to cross it. Anything drifting down the middle of the tube passes by untouched.

  3. Step 3 of 5

    So the wall is folded, then fuzzy, then fuzzier.

    A plain tubethe bare areaWith folds and villiabout a hundredtimes moreWith cell fuzz toohundreds ofsquare metres

    Ridges around the tube multiply the area by three. Millions of finger-shaped villi multiply it by thirty. Each cell's own surface multiplies it again by twenty.

  4. Step 4 of 5

    Food is pushed, not dropped.

    A ring squeezes behind Food is pushedon The next ringtakes over

    Rings of muscle squeeze behind the food and relax in front of it, so a meal is walked along the tube. It works upside down, which is why astronauts can eat.

  5. Step 5 of 5

    The last stretch is about water, not food.

    Small intestine Takes in the foodLarge intestine Takes back the water

    By the time anything reaches the large intestine the nutrients are gone. What is left there is reclaiming water — and feeding several kilograms of bacteria.

    Your gut bacteria outnumber your own cells, and there are roughly as many of them as there are people who have ever lived, several times over.

The short version

Intestines are long and fuzzy because food only crosses where it touches the wall, so folds, villi and cell fuzz buy hundreds of square metres of it.

Try it yourself

Lay a seven-metre piece of string on the floor and then coil it into a shoebox. That is roughly your small intestine.

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