How Do Our Bones Grow?

We humans are fairly squishy, and we eat fairly squishy food. So how do we grow hard bones? Learn how it happens in this episode of BrainStuff.

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Episode Transcript

Speaker 1 (00:02):
Welcome to brain Stuff from how stuff works. Hey, brain Stuff,
Lauren Volga bomb. Here, we all know that you are
what you eat, But how exactly do the things that
you eat get turned into pieces of you? I'm thinking
of bones in particular here. The foods we humans consume
are soft, especially compared to other animals diets. But from
them our bodies build strong, hard materials like fingernails, tooth enamel,

(00:26):
and bones. So how do we do it? How do
we soft fleshy humans turn soft fleshy food into bones.
Let's start off by zooming in all the way down
to the cellular level. Your body builds bone tissue with
the help of specialized cells called osteoblasts. Osteoblasts work together
forming a tight fit layer over areas where bone needs

(00:47):
to grow or be repaired. These cells secrete a particular
combination of amino acids, primarily glycine and proline. These amino
acids are the building blocks of proteins. Not unlike voltron,
they fold up with each other into something more than
the sum of their parts, though in this case it's
not a space bearing super robot, but strong triple helix
threads of protein. Your cells get these amino acids from

(01:10):
the foods that you eat. Meat, fish, dairy, and lagoons
contain both glycine and proline, and you can also get
proline from stuff like gelatine and cabbage. Once you're osteoblasts
secrete the immuno acids and they come together to form
the protein threads. Enzymes give those threads a stabilizing polish.
Vitamin C helps those enzymes work. Without it, the threads

(01:30):
can't come together to form bone tissue correctly. That's what
happens in scurvy, and it's one of the reasons why
you should eat some fruit sometimes. Cantaloup, citrus, kiwi, mango,
and berries are all good sources. The thus stabilized threads
are molecules of what's called collagen, which is the most
abundant protein in the animal kingdom. Collagen molecules packed together
into long, thin fibers called fibrals. In there many types

(01:54):
fibrals create these scaffolding that bodily tissues are built upon,
from your corneas to your blood vessels to your skin.
They're sturdy and kind of flexible, like steel beams in architecture.
They're also relatively lightweight. Adult human bones are about ten
collagen by mass, but if your bones were collagen fibrals alone,
you'd beat sentient silly putty. So to add further support

(02:17):
your osteoblasts, guide deposits of a strengthening layer of mineral
crystals along the fibrils, like pouring concrete over steel beams.
The mineral in question here is the compound calcium phosphate.
Calcium and phosphate bond in your system after you consume
foods that contain them. For calcium, that's dairy and soy products, eggs, shrimp,
and dark leafy greens. For phosphate, it's dairy, whole wheat, nuts,

(02:41):
and legumes, and this, along with dairy's amino acid content,
is why milk and fortified food adds talk about how
these products help build strong bones, though of course all
the other foods we've mentioned due to this mineral coating
is just a few atoms thick, but it gives bones
their stiff structure, and it accounts for about of adults

(03:01):
bone mass. Finally, the coated fibrils get gummed together with
a sort of shock absorbing glue made up of spiraled
collagen molecules that can uncoil when stress is applied, and
then snap back into shape. This helps prevent fractures at
a molecular level, like if you connected your steel reinforced
concrete beams with springs. Your skeleton also contains small amounts

(03:24):
of magnesium, sodium, and bicarbonate, plus a bunch of water
like by mass. So how does your body get ahold
of all of these substances. Well, your digestive system is
a fancy molecular blaster. When you eat, your teeth, gastro
intestinal muscles and digestive juices break food down to the
point that it's molecules already to be harvested. Your gut

(03:46):
bacteria helped too. There are some molecules that are cells
can't process by themselves. Our gut bacteria eat those molecules
and poop out compounds that are cells can process. The
cells in the walls of your swall intestine pass everything
that they can into your blood stream to be carried
on to maker cells like your osteoblasts. Today's episode was

(04:10):
written by me and produced by Tyler Clang. For more
on this and lots of other reinforced topics, visit our
home planet Paw Stuff Works dot com