Worldbuilding 203: Organs and Body Structures
Greetings and seriocomic! Well, I am that a lot of the time, especially in this blog! All of the blogs! Today, I will discuss… organs and body structures! How can you use them to enhance your world? A lot! But do you expect anything else from a world connoisseur like me?
Not in haggis
As per usual, it is good to start with a definition, and I think ”What is in haggis” is a good definition, right? Jokes aside,
An organ is a collection of tissues that work together to perform a singular function.
Fantastic! Wait, what’s a tissue?
A tissue is a collection of cells of the same type.
Phew! Saved that one. But yeah, a tissue is a bunch of cells of the same type. Cells come in many types: muscle cells, liver cells, skin cells, nerve cells, etc. And when you group enough of them together that can work together, they become a tissue. And if you have a bunch of tissues together (which may or may not be the same kind of tissue) that work together to perform a job, then you have an organ!
No jack of all trades
Why do we have organs to begin with? Well, to explain this, let’s take humans, looking at a person. You can have the classical jack of all trades, master of none, or you can have a highly specialised one that is master of their craft. Now, who does the job best? Obviously, it is the one who has specialised; they are the master of doing their job and beat the jack all the time–get that image out of your head!
The same goes for biology on literally every scale. Cells that specialise in doing a job are better at doing that job than cells that have to do all the jobs. Bacteria are the jack of all trades; they have to do all the jobs, and you can see that they are not very fast. Put them in a petri dish and watch them try to swim, and it is a huge disappointment. But take a fish, on the other hand, and the specialisation of the muscle cells for movement makes them able to swim thousands of times faster. That is the power of specialisation!
Cell types are specialisation of cells, organs are specialisation of tissues, so they can do their jobs extremely well. And why do they need to do their jobs really well? Well, one cell like a bacteria can be a jack of all trades because being kinda trash at everything is still good enough to survive. But when you get fat like all multicellular life, it is harder. Especially given the square-cube law which says that if you double the size in width, breadth, and length, the volume is 8 times as big (2 cubed). Volume is where everything biochemical happens. The area only increases 4 times (2 squared), which is where exchanging of molecules happens. Which is to say that the amount of activity that can happen doubles relative to the amount of flow of molecules that can happen. Think of it like an engine doubling in all dimensions , and the amount of fuel increases, but the amount of work it needs to do is now twice what the fuel provides for. Imagine this scaling on a single cell, and you can see why it will fall over dead soon.
Organs jobs
So what are all the jobs that organs actually do? Well… a lot.
Oxidation agent acquisition
I discussed in my post on alien biology that breathing can be done differently. But breathing is a form of oxidation agent acquisition. What OAA means is that you need to acquire an oxidation agent. Oxidation is crucial to the vast majority of modern life, and as I recall, entirely vital for any lifeform that requires organs. This is because oxidation releases a lot of energy for a very small amount of fuel compared to non-oxidation reactions. What oxidation is and such is not that important now beyond the fact that the “best” one, because of how good it is and how common it is in the universe, is oxygen. Reduction would technically work too, but that is for another blogpost. ANNE! Add alternate biochemistry as a blogpost topic!
Anyway, the OAA organ has as its purpose getting this agent, or oxygen in most cases, into the body, and it has to get a lot of this into the body because every single cell will want some oxygen to work. Lungs, gills, tracheae (arthropods), etc are examples of these organs. Notice what all these have in common is that they require a HUGE surface area.
Nutrient acquisition
While you need oxygen to oxidise, you need nutrients to be oxidised, and with that, you need a nutrient acquisition organ, or several. This… It’s the mouth, it's the mouth parts and teeth, chewing and all of that stuff. It is how you get whatever you eat into your body so the next part I will go into can do their job. Some have vertical chewing (tetrapods), some have horizontal chewing (many arthropods), some do the lickling with their tongue being worse than a cat's tongue (snails). If we add metal to the tongue, we get what chitons do, and they lick rocks.
Some animals even have “circular” chewing where there are rows upon rows of teeth, all shifted in a spiral pattern. All rows of teeth chew in a different direction than the one before. So it can get really weird here. But every organism needs some way to get food that is outside into the body, and this is the nutrient acquisition part. They are often on the head, for a good reason that I will get to later.
Nutrient extraction
So the food is inside, now what? Well, some of the cells got destroyed, by you, presumably, chewing, but your body and cells need it in molecules! Most cells don’t eat other cells directly, they get molecules and only take them in. Well, this is what the nutrient extraction organs do. They extract it from what you eat.
This can be a multi-organ process where many organs have to work together. Many animals, for example, have a stomach that does the pre-processing where it tries to kill bacteria and dissolve the food more. Unless you’re a spider, at which you do this in the inside of the meal before drinking the dissolved insides out of their body; imagine going to a dinner party with a spider family!
The next part is the actual extraction of the biochemical molecules from the slushy mess of pre-processed chewed up and dissolved organic matter. It’s your intestines. They do the extraction, and like the lungs, this needs a LARGE surface area to work well. This is also where bacteria can actually help a lot. So much help, in fact, that many mammals have their children checks the thesaurus once again eat the dehydrated dissolved digestions of the mother. All so they can get the bacteria to help in the intestines!
The final big part is… dehydration. You don’t want to lose too much water with this whole ordeal, so the body tries to get the water back from it all. That is the colon's job, for you humans. Some colons are, in fact, so good at this dehydration job of the food that some mammals do not need to drink. They get all their water from the food they eat.
Nutrient & oxidation agent transportation
It's all well and good that you have organs that can get nutrients and oxidation agents, but all cells need it! Not just the one that manages to extract it. Well, this is where the NOAT (Nutrient & Oxidation Agent Transportation) comes in! I am so creative. This system helps take the nutrients and oxidation agent from your organs that collect it and take it to all other organs and cells!
There are many variations here to go on. You can have the open vs closed systems distinction. What does that mean? Well, you humans have what is called a closed system. That means the entire NAOT system is contained within its own channels where fluids can travel. It is closed because unless you injure yourself, there is a separation between the NAOT fluids and the rest of the body. For you, it is called the circulatory system and has your blood.
This is contrasted with an open system, which arthropods, which have insects in it, have. In an open system the NOAT fluids are mixed in with the rest of the bodily fluids and flow around. You don't have arteries, veins, or the like that are specifically evolved to only have NOAT fluids in it; it is all a giant mixed soup of fluids that flows around all over the place and hopefully reaches the right organs.
I’d say the astute among you, but we all know you are all astute, you’re reading my blog! Anyway, the astute will know that pumping it all throughout the body sounds like it would be a lot of work if you are particularly large. Hey, we all have hearts, I have three! But even with that, it's a big ass muscle, and ours has an entire system dedicated to just doing the NOAT job, so how is it for those with an open system? Welcome to reason number far too many why arthropods tend to be on the smaller side.
Of course, there are ways around this. Instead of having just one heart, you can have multiple throughout your body, and they all pump the NOAT fluid around hoping organs don’t starve to death.
Movement
One problem that any being faces is the ordeal of me being here, but what I want or need is over there. How do we solve this problem? Well, plants and fungi solved it by doing absolutely nothing and hoping the situation would never arise or by the time the issue became a life threatening problem, they would have shot off their spores and seeds to try again.
We animals, however, we thought this was a stupid idea and developed entire systems of moving! Namely muscles. Muscles contain proteins that essentially work like springs and contract when the right chemical signal is given. Which, when pulled on each other or other structures, gives movement! This is essentially the same across the entire animal kingdom. Which brings me to…
Structural support
You gotta pull on something, otherwise not much happens. And that is where structural support comes in. It serves to help hold up the body but also helps move the body. For you vertebrates, you have what is called an internal skeleton, or an endoskeleton. It means you have all the soft stuff outside the skeleton, albeit the skeleton can help protect some of the more important ones. This has the benefit of not scaling too much with size, thus allowing bigger animals, and, relatively speaking, better anchor points for muscles with angles and the like.
The other option is for what is called exoskeleton, or external skeleton. This means that the skeleton is your outside, and all soft stuff is on the inside. This is what arthropods have on Earth. The big benefit here is that you can use it as extra defence. Unlike an endoskeleton, where you get soft tissue around the outside meaning any wound will always harm soft tissue first, an exoskeleton allows a sturdier substance to take the brunt of the punishment first before any of the soft tissue starts taking damage.
This is counteracted by the fact that an exoskeleton needs to cover your entire body, so it will grow much faster, in terms of weight, with the size of the body, than an endoskeleton will. This is reason number way too many why so many why arthropods tend to be limited in size. When they left the ocean and went onto land, which happened before vertebrates, they did change to a less dense, and thus heavy, substance for their exoskeleton, chitin. Not as strong as the original, but strong enough and way lighter.
Waste management
One of the big issues in life is that you get what you want, use it, and then you are stuck with products you didn’t want! Well, those are waste products, and all biochemical processes have waste products because matter cannot be destroyed. And your body has to somehow deal with it.
Some of the waste products are actively harmful and need to be broken down. This is what the human liver does. In other cases, you need to expel it completely because it no longer serves a purpose. Gaseous waste can be breathed out, so no big deal there. But some waste is liquid-soluble and thus needs to be dissolved or liquid themselves and mixed with dominant liquid. Usually it's water because that is what the body is mostly made out of.
So, that which can be dissolved in water is put there, which is what human kidneys are for. However, not all liquids are soluble in water, so they have to be worked into forms that can dissolve in water, which goes back to the liver then. Then, there is waste that is pure solid. There is no way around it, and it has to be expelled as pure solid. This solid substance can be troublesome as it is more difficult to deal with, especially if it isn’t in the digestive tract and kept in motion. When it is part of cellular metabolism, it is more difficult to move around as it doesn’t want to be in the water. This is why silicon life forms are more difficult to exist. Carbon dioxide is a gas, silicon oxide is solid.
Some life forms, which is in fact most animals on earth, mix solid and liquid waste into one splat out of the cloaca. Others, mostly only mammals, divide up the solid and liquid waste, through the anus and urethra.
And my vote is that just as piss is for liquid, shit is for solid, splat should be for when mixed together.
Internal Defence
In my post on diseases, I discussed, well, diseases, and later I discussed parasites. When you are alive, you are literally a smörgåsbord–that is how it is properly spelled, you åäö deficient anglophones–of food for any other organism, and that means they will try to take it from you. Not directly killing you… Well, most of the time. Sometimes your death is the better option, but usually you’re better alive to steal from.
You, my good sir, madam, madir, si’am, or whatever other one you want to use, do not want this! It is your food! Your body! Your energy! So you need to have a system in place to defend you against the intruders! I know, an immune system! ANNE! ADD TO THE LIST!
I won’t go into details here for the human system, since it is colossally complicated and extremely old. But in broad strokes, you can think of systems coming in two flavours, innate and acquired. The innate system is one you are born with and just is as it is and doesn't depend on exposure to pathogens, or antigens. This is contrasted with the acquired immune system which depends on which antigens you’ve come across. If you never come across a pathogen, your acquired system will never learn how to defeat it.
Some animals, especially short lived ones, rely heavily on the innate system because they only need to survive a short time, have lots of sex, get babies, and then die. Pathogens don’t have a lot of time then to attack. Some animals in fact have their entire system not geared toward defeating pathogens, but to suppress the illness just long enough to get the next generation going and then die by the illness. Think of it being essentially born sick and then running a 40 celsius fever for your entire 4 year lifespan, then you flop over dead.
Larger animals that live longer tend to prefer focusing on the acquired immune system; it is more efficient long term and can actually defeat pathogens. The big downside is that for the first infection, it is SLOW. It is slower than a decaffeinated hung over student on a Monday morning (I am a teacher and I get to make this joke). But once the acquired system has learned a pathogen, it is ruthlessly fast and efficient.
Great system, unless it goes haywire and starts destroying its own body… which is actually the primary cause of death when it comes to diseases. The body’s own system to defend itself attacking and killing the body. MOVING ON!
Processing
You know what's better than surviving? Thinking! At least I think so, thinking is my favourite hobby! Anyway, when you get inputs–that is, senses–and outputs–that is, muscles–you need some way to correlate what inputs at what times should result in outputs. This sounds like a mathematical or computer function…
That is because it is! This is why, for example, neural networks in computers work so well. They can model any kind of function, and that is what brains do. It is a highly complicated processing unit that has an architecture that can mimic any function for amount of inputs to any amount of outputs!
But just because a brain can do this, it doesn’t mean it has to all be done in the same way. Vertebrates have a highly centralised brain where it all is located. And surprise surprise, it is in the head. The focus of the brain, eyes, mouth, nose, and such all at the same place is called cephalization and is a recurring phenomenon that has happened more than once. The reason is simple: you need to eat with the mouth, so it helps having eyes, nose, and taste all localised right there then. And when you have all those so close together, it is efficient to have the central processing unit near it all, less lag.
This is, however, not the only option. Octopi, for example, have a more decentralised system where there is a central brain, but each of the tentacles have like a mini-brain that controls the tentacle and processes its inputs to do the job that the main brain tells it to do. So you can go for this, too. The way I heard it described is this: a human brain has a map of how the body works, and when it wants something done, it uses the map to send signals to muscles to do what it wants the body to do. An octopus brain knows it has these other mini-brains, so if it decides that a job has to be done using one specific tentacle, it tells the mini-brain to do the job, then the mini-brain has to figure out how to do the job and the main brain doesn't care how it’s done.
Summa summarum
I have almost certainly missed some functionalities, and if I have, another post will, eventually, come. But when you make organs, think about what job they are performing. Many of the jobs mentioned here require many steps, and a lot of human organs combine jobs into one organ, but other times, they are split into finer separate jobs.
The benefit of specialisation is efficiency, so more specialised means more efficiency at the job. It also means a more fragile structure if anything is damaged, so there is a trade off. So find the balance that fits you, or that you find funny. I put a heart in the butt of my Limaces because I found it funny, and it made enough sense.
So keep in mind: organs exist to work to keep an organism alive, they don’t just randomly exist. Either they ARE doing a job, or they DID a job in the past, but useless things do not stick around for a long time. And no, the appendix is not useless, it serves an important job for the gut bacteria… It isn’t a required job, but it helps having it!
And with that, I bid you adieu, and I am going to go and let my organs, especially the squidgy spooch, do their jobs!
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