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Writing: Input Wanted Is it useful to have 2 stomachs?

  1. Sep 20, 2016 #1
    Here I will talk about the digestive system of my Kepler Bb humanoids.


    The teeth are much stronger than bone(Strong enough that they can eat bones no problem). Other than that and all time tooth formation(so a loose adult tooth is no problem for them since another will grow in its place), they are pretty much human in the mouth.


    Not much difference here besides length and time it takes for food to go down the esophagus.


    This here is where it differs the most. There are actually 2 stomachs connected to each other but they each have different roles.

    The first stomach is the one most likely to get infected and is where chemical and mechanical digestion take place.

    The second stomach is less likely to get infected and is used as an antinausea defense. If the first stomach is too full, only a little bit of food goes to the second stomach. If the first stomach is infected, all the food goes to the second stomach. Here only chemical digestion takes place.
    There is a sphincter that separates the 2 stomachs which I call the gastric sphincter. This is why food doesn't always go into the second stomach.

    In the second stomach, once it gets full enough it starts pushing the partially digested food into the first stomach which then lets it through bit by bit into the intestines.

    The liver, gall bladder, and pancreas are just like the esophagus in that there is little to no difference.


    Here there are some differences. For 1, the small intestine has even more absorptive surface area than ours. Second, there are glands in the small intestine that secrete their own digestive juices. The large intestine has a longer appendix that isn't useless at all and won't burst simply from inflammation. So a humanoid can have appendicitis several times in its life without an appendicular rupture(rupture of the appendix). Other than that, the large intestine, rectum, and anus are just like ours except for size.

    Anyway, is it useful to have this gastric sphincter and second stomach as an antinausea defense and to have the second stomach push stored food into the first stomach instead of pushing it directly into the intestines?

    Digestive System Images:
    Humanoid Digestive System at rest.png Humanoid Stomach.png Humanoid Digestive System, Digestion in Stomach, no bones.png Humanoid Digestive System, Digestion in Stomach, bones.png
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  3. Sep 20, 2016 #2

    Vanadium 50

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    Do you expect this to attract readers?
  4. Sep 20, 2016 #3
    Well this digestive system is not talked about in detail in my story but since this is important as to why these humanoids are different from us but also so similar, I would expect some readers to be attracted to this, especially readers that are also biologists.

    I couldn't put this in biology since this is about a fictional digestive system, not a real world one.
  5. Sep 21, 2016 #4


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    What stops evolution from simply getting rid of the 2nd stomach? Is nausea that big a deal?
  6. Sep 21, 2016 #5
    It isn't just nausea and vomiting that caused them to evolve a second stomach. It is also a diet that includes eating bones on a regular basis. Bones get diverted to the second stomach where an enzyme called CalciPhosphatase can digest the bone into minerals to be absorbed into the blood.

    But prehistorically, for this species, stomach flu meant big trouble. Predators would attack them more often, some people starved to death or died from dehydration as a result.

    Nausea resistance was first evolved and then later on a second stomach and gastric sphincter. This second stomach made nausea resistance worthless because nausea would signal the gastric sphincter to let some or all the food into the second stomach depending on severity and cause. Later on, as they started eating more bone, a special enzyme was needed. Gastric acid just wouldn't cut it. This also meant tougher teeth and esophagus needed to develop. So generations later the second stomach started making CalciPhosphatase for digesting bone. Even later when special powers got into their genetics, food storage during digestion became incredibly important for morphing powers. So the second stomach gained uses over the millennia and now with so much importance, there is just no way that getting rid of that second stomach would help the species. So genes for a second stomach thrive but genes to get rid of that second stomach don't.
  7. Sep 21, 2016 #6


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    I assume that was implied but unstated in your first post? :wink:

    So they started eating bone before they developed the mechanism to digest it?
  8. Sep 21, 2016 #7
    The second one can act as an intrusive guy to help the first one from having to vomit from time to time, which may lose other good nutrients altogether. Also, the two guys can grind all the foods in better and out for later better absorption done by the du-je-ill eums. In general, it's a very good idea to me. :oldbiggrin:
  9. Sep 21, 2016 #8
    Yes but in very small amounts that gastric acid itself could digest. When they had an enzyme for digesting bone, they started eating it in larger amounts. Eating bone is important in them during pregnancy to get the bloodstream in a high calcium state so that the fetus takes as little of the mother's bone as possible(and in some cases none).
  10. Sep 21, 2016 #9


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    I didn't think that gastric acid could dissolve bone, but other than that I suppose this is mildly plausible at least.
  11. Sep 21, 2016 #10


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    I think of nausea as a generalized defense response to bad stuff in the stomach. Vomiting gets rid of that bad stuff and therefore serves a useful function in avoiding poisoning, among possibly other things. This is something which evolved long ago (shared in many species) due to its adaptive value. Just because it feels bad does not mean it should be gotten rid of, nor that it would be selected against.
    The Garcia Effect is a behavioral response to nausea, where foods similar to those eaten prior to nausea are avoided afterwards.
    I think (at least in our circumstances) the nutrient loss would be balanced by the avoidance of poisoning in an evolutionary sense.

    Cows and other multi-stomach critters use their different stomachs for different functions. One is predator avoidance. The strategy would be eat fast, store incompletely chewed food in a storage stomach, get out of the open field where a predator has a better chance of finding you, then rechew and digest the food in a different stomach.
  12. Sep 21, 2016 #11
    But nauseous people and people throwing up attract more predators to the whole group(To a predator, nausea is a weakness). Plus, what if it is severe? Dehydration and Starvation would surely be causes of death in that case.

    Sure, vomiting might get rid of poison but it also gets rid of nutrition, bile, acid, and can cause blood pH to go up and thus give you alkalosis. To me, storing nutrition before throwing up(so in the nauseous state) in a separate stomach and then letting the acid and bile and poison out is better than letting everything out. And not all causes of nausea have to do with poison or infection. Sometimes it is just being overfull that causes nausea, another reason to have 2 stomachs. Sometimes it is high hormone levels(particularly in females). And sometimes it is severe pain. Gastric obstruction could cause nausea and vomiting along with extended digestion(though an obstruction not letting food out of the stomach is rare). Reflux can cause it.

    Those are all examples of non infectious, non poisoning, causes of nausea.
  13. Sep 21, 2016 #12


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    The risk of attracting a predator is almost certainly lower than the risk of getting very sick if you don't get nauseous and vomit.

    Of course. But the fact of the matter is that nausea and vomiting serve a useful evolutionary purpose, saving more lives than they take in the long run.

    You can't separate the toxic/poisonous material from the non toxic/poisonous in the stomach (well, we can't). You'd need another way to filter it out, and since there are many different chemicals and bacteria that cause nausea, there's really no single way to reliably filter them all out anyways. Vomiting is the simplest and quickest method of getting rid of the stuff that can make you sick.

    So you don't eat for a meal or two in most cases of nausea, so what? And though I haven't looked into it, I'm betting alkalosis from nausea and vomiting is very rare.

    Some of your examples, women's hormones making them vomit during early pregnancy for one, probably serve a useful purpose. I know I've read about possible evolutionary advantages of it. I'd also think that nausea from a gastric obstruction would be beneficial as well.
  14. Sep 21, 2016 #13

    jim mcnamara

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    Back to square zero:
    Applying Biology - your second stomach is a dead end. So it appears that stuff goes in, cannot go out. The only parallel in our gut is the appendix - it acts as safe storage for our gut flora in the case of severe diarrhea. Post-diarrhea the gut can be reinoculated with beneficial bacteria and friends.

    Dead ends in the gut cause lots of problems - the death rate from appendicitis was substantial prior to modern medical treatment.

    Take that FWIW.
  15. Sep 21, 2016 #14
    The only problem with that assumption is that just like the first stomach, the second stomach has smooth muscle tissue. Stretch and fullness stimulate contraction of this muscle but only after both stomachs are finished digesting whatever is in them.
  16. Sep 22, 2016 #15

    jim mcnamara

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    What are you talking about - your diagram shows a dead end stomach - no pylorus for #2. Unless you want to reinvent a lot more than you indicated.
    Stomachs have an input and a separate output. I realize this is fiction but you wanted to treat this exercise logically - or so I thought. How do you want to get stuff in #2 back up into #1, since #2 is marked "storage"?

    You do realize that lots of Earth ruminants (cows, deer, etc.) have mulitple "stomachs" If you look at this picture you can see that the rumen kind of recycles partially digested food, it acts somewhat like your idea storage. But there is a direct connection to the omasum, which is down "south" of the rumen. Try this cow model for your alien. Then you can have "moo-tiple" stomachs.

    And yes, it can be very useful to multiple stomachs if your food has a very low net yield of food energy and nutrients. They just need usable plumbing.

    http://www.extension.umn.edu/agriculture/dairy/feed-and-nutrition/feeding-the-dairy-herd/img/0469f01.g [Broken]
    Last edited by a moderator: May 8, 2017
  17. Sep 22, 2016 #16
    That's how I designed it is so that at some point, smooth muscle contracts in the second stomach to send it up to the first through the gastric sphincter and then the first stomach sends it to the intestines through the pyloric sphincter.
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