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.
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.
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.
|A nephron and its|
regions. We'll get into this
in another post.
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.
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.