The Breath of Life Part 2
So I wrote The Breath of Life Part 1 over a year ago and I THOUGHT I had written a part two but apparently, no, just no. :/ So after much dealy and with no particular reason for it other than that I noticed I didn’t do it: The Breath of Life Part 2.
A Centaur CAN’T breathe like a human or a horse and survive. It just can’t get enough O₂.
But there are living (and extinct) animals that can get enough O₂ for the metabolic needs that a Centaur represents.
For living animals, it’s avians, but there’s mounting evidence that dinosaurs and certain modern reptiles and amphibians breathed in similar ways to cause the same effect, so this kind of power does scale.
The Way bird lungs work is a bit more complex than human lungs.
A human (and a horse as well) takes in a breath, filling its Aveolar sacs with fresh oxygen. The Aveolar sacs sit next to the blood flow, O₂ permeates across the thin membrane into the red blood cells in a gas exchange for the CO₂ in the blood cells. The human then exhales the CO₂. That’s a two Cycle Pattern. Inhale O₂, Exhale CO₂.
Avians have a four cycle pattern. So they take two breaths to our one for a complete cycle.
They inhale fresh O₂ which goes primarily into their Posterior Air Sacs but also a little into their lungs. On the exhale, that breath of O₂ is pumped from the Posterior Sacs into the Lungs.
While a second breath repeats the above with a second breath of fresh air, the first breath continues to move through the second half of the pattern.
On the 2nd inhale, that original breath is pumped across the Lungs toward the Anterior Air Sacs. On the second exhale, the air, now essentially empty of O₂, is pumped out of the Anterior Air Sacs (and just a little from the lungs) and back out the trachea to be exhaled.
Like in mammals, the exhaled air does mix a little with the inhaled air inside the dead space of the trachea, but that also performs a function of warming and moisturing the incoming air in exchange for cooling and drying the outgoing air. This prevents some heat and moisture loss and makes the system run more efficiently.
There is no gas exchange in the Air Sacs. They simply pump air. Birds tend to have between 7 and 9 air sacs in order to make this all work.
All gas exchange happens in the lungs. And because of the air sac arrangement, the flow of oxygen is unidirectional. This is what allows it to be so much more efficient than humans (and horses). While we place O₂ next to blood in a sac and let blood flow across it for the exchange. Avians have two currents. The air flows one way, losing Oxygen as it goes. The blood flows the other way, gaining Oxygen as it goes. Because of the longer track of exchange, more O₂ can be removed, if the first red blood cell it touches doesn’t make the exchange, the thousandth one will. By the end of the route, nearly every bit of O₂ has been extracted, so the exchange gets darn close to perfect.
The result of all of this is that avians tends to have a proportionally smaller lung than mammals but actually much more space devoted to the respiratory system. Those sacs take up a lot of room. For the overall system, a bird will devote about a 5th of its internal organ space to lungs while a mammal will only devote about a 20th, 4 times less. So if we give Centaurs this system, their lungs are a much more prominent feature than in a human or a horse and other efficiencies are going to have to be worked out elsewhere.
Besides for the fact that I simply can’t stomach two spines...
What is that?? Just no. I can’t. That’s a structure designed to fail, and there are just too many of those already in this system.
One of my reasons for scaling up Centaurs is that I don’t think they’re going to be barrel sprinters.
They can go fast. They can have a lot of power. But I think no matter what you do, they’re going to be a bit on the cooler side of what they can do. In the end, they have a lot of needs for the space they have. A normal equine with the same dimensions of a Centaur’s horse part is going to be smaller, faster, better balanced.
Cooler blooded simply seems implied to me. So I’m scaling them more like a draft.
Or in the particular case of the Centaurs I’m thinking of for “The Coward Gloria Foxfoot” (assuming I pick it up again) more like a Pygmy Giraffe for the sake of that spine but it comes to the same thing. So bigger, slower, calmer. Which will also mean they require a bit less in the oxygen needs department anyway. With more room to stuff all that internal organ mass they’re going to need.
They’ve got room for all that lung and their mass is going to be something to behold.
But more efficiency is needed before Hole-in-the-Sky is ready to take Gloria Foxfoot on their first campaign. So hopefully The Breath of Life Part 3 (a little less breathy) will take less than a year to get to.
