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| Big & Heartless; Could peristalsis alone do the trick? | |
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| Topic Started: Jan 10 2011, 07:52 PM (530 Views) | |
| Rhob | Jan 10 2011, 07:52 PM Post #1 |
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Adult
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So in the novelization of Independence Day (NERD ALERT), the alien invaders were said to lack hearts (*rimshot*). Instead, their blood was circulated through muscular peristalsis. My question is, could that actually work in an organism that large -- roughly human-sized? |
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| Empyreon | Jan 11 2011, 02:45 AM Post #2 |
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Are you plausible?
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Some sort of uber-peristalsis doesn't seem outside the realm of possibility, IMO, at least for aliens. There may be something about the nature of tetrapod veins that largely eliminates the possibility (I don't know). However, the larger the creature the more it would benefit from some kind of circulatory nexus where oxygenated blood goes to the rest of the body and un-oxygenated blood travels to the respiratory system. That nexus would likely develop pumping muscles, and you have a heart. To make a heart-free system work you will have to find another solution for getting oxygenated blood to the whole body. |
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Take a look at my exobiology subforum of the planet Nereus! COM Contributions food for thought
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| lamna | Jan 11 2011, 03:36 AM Post #3 |
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Perhaps it would work better if the creature has breathing holes all over its's body. |
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| Rhob | Jan 11 2011, 11:58 AM Post #4 |
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Yeah, one concern could be scalability. I'm not sure how well smooth muscles scale down. They might not be able to work at the capillary level, for example. But that's probably not a big deal, since bloodflow through our capillaries isn't propelled by muscular peristalsis, either. EDIT: There are things called precapillary sphincters which are made of smooth muscle.
Good point. The muscles which provide peristalsis for the vein-analogues would need some way to be oxygenated. Yet the blood moving through them is deoxygenated. However, Wikipedia says that the inner lining of veins is made of smooth muscle. While not engaging in peristalsis, apparently it stays flexed to maintain a particular volume. In addition, capillary beds aren't very thick. Presumably the venous smooth muscle is oxygenated and nourished from the capillaries as well. Finally, it's interesting to note that there are non-pulmonary methods for getting venous blood back to the heart. Vertebrates have what's called a skeletal-muscle pump which helps return venous return. In mammals, the diaphragmatic breathing mechanism also contributes.
This comes close to describing a tracheal system, doesn't it? Or is that your point?
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| Empyreon | Jan 11 2011, 05:14 PM Post #5 |
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Are you plausible?
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That may be a concern, but the entire arterial length doesn't have to be peristaltic, only enough to keep things flowing. Like you said, capillaries aren't peristaltic, and to my knowledge neither are veins. If enough of the arterial length can keep the blood flowing then the rest of it can be more like what we're familiar with. An interesting implication that comes to mind would be much less danger of fatal heart attacks. If one section of the system dies out, the others could pick up the slack, keeping blood flowing to necessary organs. |
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Take a look at my exobiology subforum of the planet Nereus! COM Contributions food for thought
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| colddigger | Jan 11 2011, 09:38 PM Post #6 |
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Joke's over! Love, Parasky
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A combination of a tracheal system and having oxygenated blood moved by smooth muscle contraction, could it work? |
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| Rhob | Jan 12 2011, 02:31 PM Post #7 |
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Right, I agree. There's another problem I stumbled upon, however. First let's simulate a band of circular smooth muscle as an open tube. If the walls of the tube contract, the diameter of the tube will decrease and therefore the length of the tube must increase. The increase in tube length will also be equal on both sides. So it seems that some additional mechanism would be needed to keep blood flowing in one direction. What do you think?
Hmm, interesting. Are you implying that a peristaltic circulatory system would necessarily have more redundancy? Or maybe the circulation would be more open?
Maaaybe... the tracheal system would have to be different from that of insects. However, the spiracles could draw in more oxygen if they're surrounded by contractile circular muscles. This same contraction could drive the flow of oxygenated blood away from the spiracles. Is that what you're thinking? |
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| colddigger | Jan 12 2011, 03:32 PM Post #8 |
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Joke's over! Love, Parasky
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Preeeeetty much, I mean if it's a big critter it can't rely on the air passively flowing in the tracheal system... But with a tracheal system the organism wouldn't have to rely on the blood as heavily for oxygen (if really at all -if it can work-) and so it could have a far lower need for an intense blood flow. |
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Oh Fine. Oh hi you! Why don't you go check out the finery that is SGP?? v Don't click v Spoiler: click to toggle | |
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| Empyreon | Jan 12 2011, 04:13 PM Post #9 |
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Are you plausible?
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Tracheal respiration will work in atmospheres rich with oxygen, but if there isn't enough to run larger bodies then something more efficient and/or complex will have to develop.
Well, how does the esophagus do it? Also, could some sort of structure akin to our tricuspid valve periodically positioned to prevent blood from "backwashing"?
That's where my line of thought was going, yes. If our heart stops then blood stops flowing and the rest of the body dies quickly. If a length of artery dies out in this organism then there might be a hiccup in the overall system, or a general lowering of blood pressure resulting in less activity, or something along those lines. Edited by Empyreon, Jan 12 2011, 04:13 PM.
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Take a look at my exobiology subforum of the planet Nereus! COM Contributions food for thought
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| Rhob | Jan 12 2011, 06:00 PM Post #10 |
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Adult
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The only issue with an actively-ventilated tracheal system is how waste gases would be exhaled. In insects, I'm pretty sure that both O2 and CO2 are passively diffused.
The esophagus contracts behind the food bolus as well as in front of it. I don't think that would work with blood, since you need a more continuous flow. Human veins have one-way valves to help blood flow back to the heart. Arteries in a peristaltic circulatory system could have those as well, though I'm not sure how well they'd have to correlate with the circular muscle bands.
Ah, right. I'm not sure why I didn't quite get that before. Yeah, the circulatory system would be much more distributed, so "mechanical failure" in one part wouldn't take out the whole system. That might make such creatures harder to kill in some ways, too.
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| Empyreon | Jan 12 2011, 06:10 PM Post #11 |
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Are you plausible?
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Indeed. You can't shout, "Aim for its heart!" Rather you'd have to inflict enough damage that blood loss will drop it, or aim for its brain instead.
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Take a look at my exobiology subforum of the planet Nereus! COM Contributions food for thought
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| Rhob | Jan 13 2011, 11:13 AM Post #12 |
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Adult
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So I've been reading about invertebrate circulatory systems. The setup of earthworms and other annelids is interesting. While typically described as a basic closed system, Wikipedia states that it has a "vascular sinus" in the gut wall. It might be better, then, to describe it as semi-closed. Even more interesting, the earthworm cirulatory system is partly driven by peristalsis! Of course, earthworms are much smaller than people. I'm almost positive that the "need" for more efficient circulation is driven by decreasing surface-area/volume ratio as the latter increases. That's why open circulatory systems become problematic for large(r) animals. Tissues need to start being perforated -- vascularized -- in order to get the oxygen and nutrients they need. Also, the blood return path needs to become more regularized. I can see a sort of "hybrid" circulatory system where organs are surrounded tightly by blood sinuses (to better drive the blood into the tissues) and having closed veins for returning blood back to the lungs/gills/etc. Both the arteries and veins could be driven by peristalsis. |
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| Rhob | Jan 17 2011, 12:28 PM Post #13 |
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Any other thoughts on this, Empyreon? Colddigger? Anyone else? |
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You can't shout, "Aim for its heart!" Rather you'd have to inflict enough damage that blood loss will drop it, or aim for its brain instead.
2:31 PM Jul 11