Since I was little, one
bodily process has weirded me out more than all the others.
How is it that you can
drink a big glass of milk, go pee half an hour later, and it be clear? What
happens to that milk for it to turn from opaque white to clear, and in such a
short period of time?
As a kid, I imagined a sort
of sieve, like the really fine sifter my mom would use for powdered sugar on
cookies. In my mind, I could see it at the bottom of the stomach, filtering out
all the tiny molecules that made milk white. What was left must have been
clear, likely water, and came out as pee. That was one efficient sifter, I
thought.
As I went through my
biology classes in high school and college, I got a better idea of this magic
milk transformation. Your stomach digests foods physically and chemically.
Maybe some of the acids helped to break down the milk, I thought. I learned
that the kidneys are really the ones responsible for taking stuff out of fluids
and producing urine. So it wasn’t my mom’s powdered sugar sifter after all.
I didn’t really get a good
grasp on the process until I took Animal Physiology later on in college. Dr.
Henry, reputed at Auburn as one of the toughest professors in the College of
Science and Mathematics with the highest failure rate, went into detail about
the human body to an extent I never expected to delve. We talked about how
nerves work, how hormones work, how electricity in the body works, and all of
the chemical processes behind these things. I had some gray hairs and no social
life by the end of the semester, but I made it out with a B. Almost more
satisfying than that B was the understanding Dr. Henry gave me about how the
heck our bodies turn milk clear.
Let’s follow milk’s journey
through the human body.
1. Stomach
First off, milk is broken
down by an enzyme released in the stomach. Lactase gets in there and breaks up
the milk party, turning the milk into basic components like sugars, salts,
fats, and water. People who are unable to manufacture this enzyme in adequate
amounts or at all, are lactose-intolerant.
2. Bloodstream
Parts of your digestive
system are connected to your liver by what’s called the hepatic portal system.
The remnants of that milk you just drank are now floating around in your
bloodstream, being fed through your liver, and throughout the blood highway
system of your body. To your brain, to your pinky toe, to your eyes, you name
it.
3. Kidney
 |
| A nephron and its absorption/reabsorption regions. We'll get into this in another post. (wikipedia) |
Your blood is run through
another filtration organ- the kidneys. Our kidneys, in a way, are sifters.
Though, they are chemically-driven sifters, rather than physical ones that let
things through based on size.
A nephron is a single unit
in the kidney. We have a about a million in each kidney, and they’re constantly
running blood through and using concentration gradients to pull out unwanted
molecules and retain necessary ones. And a nephron is no simple little tube for
diffusion. A nephron is a complex thing, with and functional structures and
parts that are named after people. The details of how a nephron works warrant a
completely new blog post, so we’ll save those for later.
Long story short, the
nephron takes what you need from the blood- like say, the calcium from that
milk- and gets rid of the rest in the form of urine.
4. Peeville
Urine drains from your
kidneys through tubes called ureters to your bladder. Here, the unneeded milk
components (water likely being a major component) sit and wait until you get up
and go pee. The rest is history.
I dare you to go chug a big
glass of milk and see how long it takes for you to have to go pee. If it’s like
me, it’s a matter of minutes. The fact that our bodies can do all this in half
an hour or less is crazy to me, and even cooler than the powdered sugar sifter
in the stomach hypothesis.
It’s also a tangible
reminder of how quickly and efficiently our bodies absorb what we put into
them- good and bad.
Just some things to think about.
