After the food is liquefied, our bodies need
to absorb both water and the nutrients our
bodies need: fats, proteins, and carbohydrates.
Almost nothing is absorbed in the stomach. Food
is mostly just broken down there.
In the intestines, there’s still some breakdown,
but also a lot of absorption. Absorption
takes a long time. Only the stuff right next to
the cells in our intestines can be absorbed, so
our bodies have ways to increase what we call the
surface area of the intestines. This is the
surface that actually touches the contents of the
intestine. For one thing, the lining of our
small intestine has lots of tiny finger-shaped
things called “villi.” These increase the
area just like a glove has more surface area than
a mitten. Each cell also has tiny
microvilli. All of this puts more cell
surface next to the stuff in the intestine (called
“chyme” and pronounced KYME).
Muscle contractions of the intestines slowly move
the chyme and mix the chyme with enzymes that
break it down. This movement and mixing also means
that as the cells absorb the nutrients from one
part of the chyme, a different part is pushed next
to the cells. If this didn’t happen, nutrients in
the middle of the chyme would never touch the
In the large intestine, most of what is being
absorbed is water. By this time, the stuff in
the intestine is a lot more solid. The large
intestine doesn’t have villi because the mass is
too solid to flow around the villi. Instead, there
are pits that tend to gather the water. Absorbing
water also takes time.
If someone’s intestines were moving really fast,
what do you think would happen to their ability
to absorb nutrients? How might their trips to the
bathroom be different?