The Most Valuable Liquid On Earth?
Over the last hundred years science and medicine have collaborated to become rather good at replacing failing body parts.
There are new hips to keep us dancing, dialysis machines to do the work of our failing kidneys and even artificial hearts to keep us alive and out of hospital for years whilst we’re waiting for our heart transplant.
Impressive.
But more than 400 years after William Harvey explained blood’s journey through blood vessels, science still hasn’t created a synthetic “blood” useful for much beyond decorating Halloween outfits.
Surprised?
Blood’s an incredibly complex, multi-functional liquid without which we never would’ve become the walking, talking, thinking (sometimes!) creatures we are today.
Need convincing?
How about..
.. its role as chief transport officer for our immune system’s bacteria and virus-nuking agents, our white cells and antibodies?
Or ..
..its distribution of hormones around the body, responsible for everything from the growth of our skeleton to the development of hair in funny places?
And don’t forget..
.. after we’ve indulged our passion for fruit cake? It’s blood that’s going to move those nutrients from our gut to our active, hungry cells.
Spot the common theme?
All of these functions rely on blood’s capability to pick up, drop off and repeat again and again! And it’s blood’s ability to collect and deliver oxygen around the body that hands down, is its most important function and the reason we’ll die if we lose too much of it!
Everyone’s blood follows the same, specific route around the body, starting its journey in the right side of the heart which pumps it to the lungs for the crucial oxygen pick-up.
The oxygen-infused blood then flows back to the left side of the heart to be pumped out to the body, traveling through thousands of miles (not a typo I promise) of blood vessels and delivering oxygen to trillions of cells before returning to the right side of the heart…
… to almost endlessly repeat this circuit.
Slumped in front of Netflix for an hour? Our 5 liters of blood makes that trek around 60 times. But hit the Peloton for an hour and our blood might complete that same journey hundreds of times to make sure our cells get all the oxygen needed.
What’s in these lovely liters that’s actually doing the oxygen delivering?
What’s the “something” so complex, that science can’t copy it?
Red blood cells, jam-packed with a red, iron-rich protein called hemoglobin, make up not quite half of our blood. And it’s those hemoglobin passengers riding inside the red blood cells (or erythrocytes, as they’re scientifically called), that are responsible for the collection and delivery of oxygen molecules.
Bone marrow within our skeleton continuously assembles new hemoglobin-laden erythrocytes before dispatching them into the circulation where they’ll spend their entire 4-month life span constantly repeating that same heart, lungs and body circuit. Eventually though, exhausted and fragile, they’ll head to the spleen and liver to be broken down and recycled.
The skeletal production line is truly the eighth wonder of the world, working constantly to replace not only those tired, old erythrocytes being broken down at end of their life but the ones lost in a hundred different ways, everything from a skinned knee to a nose bleed.
Take it from me (or head over to the geek notes to see my math), keeping the right number of erythrocytes needs a production rate of at least 3 million new erythrocytes every SECOND!!!
However, bone marrow needs oversight to keep up this rate of manufacture and that job falls to our kidneys and their release of the hormone erythropoietin (EPO) into the bloodstream. As long as blood keeps moving EPO from our kidneys to our bone marrow, then our daily erythrocyte production should keep up with our daily erythrocyte destruction.
What happens if we temporarily relocate to a mountain in Colorado or generously gift one of our precious pints? Because our kidneys are always monitoring the amount of oxygen in our blood they’ll recognize when there’s not enough oxygen circulating and increase their EPO output. More EPO arriving at the bone marrow cranks up the rate of new cells rolling off that production line until we have enough extra erythrocytes to bring blood oxygen delivery up to a normal level.
Brilliant!
(EPO is precious stuff and the reason for both Lance Armstrong losing his cycling titles and Michael Phelps sleeping in a tent. Intrigued? We’re already working on a future post about cheating in sport!)
Despite the simple elegance of this scheme, across the world around about 25% of people have anemia - meaning their hemoglobin levels are too low.
Although there are many different types and causes of anemia, for the majority of people, the issue is a very simple one – not enough iron to make those hemoglobin molecules and fill those erythrocytes.
Remember that bone marrow making 3 million erythrocytes every second because every second, the same number are ending their days?
Whilst the liver and spleen are good at recycling erythrocytes, they’re not 100% efficient so we’re always losing iron from the body. If there’s a mismatch between this iron loss and new iron arriving via our diet, we’re at risk of iron-deficiency anemia. Throw in a monthly blood loss taking with it even more iron and it’s easy to see why a 25-year-old woman is a whopping ten times more likely to have anemia than her twin brother!
Unfortunately, getting enough iron to our bone marrow isn’t as easy as taking a mega-supplement.
We never move more than around a third of our dietary iron, across the wall of our gut and into our blood stream for the bone marrow to grab and use it. That means at least 2/3 of all the iron we eat, whether in food or a supplement, straight away exits …. in our poop!
Please don’t think of this as an evolutionary mis-step - too much iron has all sorts of health-damaging effects, including the ultimate health-harming effect, death! And even with this poor iron movement from our gut to blood, thousands of people suffer iron poisoning every year, mostly children mistaking a supplement for candy. Thankfully, most of these cases don’t end in tragedy, reflecting the tradeoff that evolution has made between the need for iron for hemoglobin production and preventing iron toxicity!
And for anyone who suspects they may be anemic?
Head over to the Geek Out pages for some good, peer-reviewed research and medical articles that give useful information on how to get the best out of our dietary iron.
But as always, talking with the appropriate health care professionals is absolutely the way to go.
Stay curious,
