The Kidneys-A Brief Evolutionary Story
Once upon a time, a very very very long time ago, you and I were very small creatures floating freely in the vast oceans of the earth. How small were we? We were tiny, just one cell big. To put that into perspective, we are much bigger now, about 60 trillion (60,000,000,000,000) cells bigger.
Life was easier then. Floating in an ocean full of nutrients, we took in what we needed directly from the environment and got rid of any non-useful substances in the same way, released directly from our little bodies into the sea around us.
Well, it seemed like getting bigger might be a good idea, and so we started adding more cells to our bodies. Life was still pretty simple at first as these cells could still interact directly with the environment around them, pulling in foodstuffs, releasing wastes.
Over time we became even bigger and had to start evolving ever more complex ways of getting nutrients to every single cell (they all need to ‘eat’), no matter how far inside of the body they were. And as always, we had to have ways of getting rid of the waste products (they all need to ‘poop’).
Things got distinctly more difficult as we made our way to land. Now, we had to adapt to a wholly new environment. Extracting nutrients from the atmosphere, locomotion on solid earth, protecting ourselves from direct sunlight, new food sources, and getting our water needs met.
Our bodies became ever more complex. And larger. And we developed decidedly more complex systems. A respiratory system to help extract oxygen from the air around us, and release the gaseous byproduct. A digestive system to take in, absorb and excrete food. Strong skeletal muscles to move us around. And a pseudo-ocean inside of us, the bloodstream. Through an elaborate circulatory system, this became the highways, roads and paths inside of us to deliver what was needed to every individual cell, no matter how tightly hidden away, and the ability to get rid of all the unwanted materials.
But the blood traveling through the circulatory system is a closed system, going around and around and around. No outlet unless we are bleeding. So what was needed was a filter and removal system. This filter would ‘read’ the blood, and while keeping the vast majority of necessary substances such as water within our bodies also the ability to remove toxins, excesses and waste products.
The urinary system is just such a device. After the blood is filtered, the unwanted portions are sent down to a storage unit (the urinary bladder) where they stay out of harms way, until till time to eliminate them
At the heart of this system are the two kidneys. Their goal, is to maintain homeostasis, that is, keeping things at normal levels in the body. They do this with about 1 million small tubes called nephrons. Each one of the nephrons independently filters to insure the blood is kept right and proper, the correct proportions of things. A massive amount of blood is sent through the kidneys each day, about 45 gallons (180 liters) pass through each 24 hours. And of all of this only about 2 quarts (2 liters) are excreted as urine. 45 gallons! A day! Imagine an average size garbage can, that’s about the right size. And now imagine dipping a quart size canning jar in and removing 2 jars worth of fluid from the garbage can. Of course we don’t have that much blood in us, we have about 1.3 gallons (5 liters) so it is constantly re-circulated and re-scrutinized.
So the kidneys are the guardian filters of the blood. And the blood is the thoroughfare from which most substances move throughout our body. Their well-being is essential for overall health. They help maintain the closely guarded pH of the blood, the electrolytes (important elements such as sodium and potassium). They help regulate blood pressure, and a variety of other important functions.
But this is not a dissertation about the kidneys, no, this about one organ system that allowed us to evolve from the very simplest of organisms floating in a very large bath, to the exceedingly complex creatures whom we now are.
And the journey is not finished.
Postscript. I realize that this is way oversimplified and I left out many other important bodily systems (reproduction anyone?) and I took other poetic license as well, after all, many of our body systems were adapting and changing at the same time. But I wanted to filter it down to this bare kidney story. I hope you have found it entertaining.