What would spiral-shaped lungs be good for?

Question

So I’m sitting here populating my alien world with critters to run around, eat each other and do critter stuff (as is the custom). At some point a thought came over me that their organs should be weird crazy shapes to mix things up a little.

What are spiral lungs good for?

The organs are sort of shaped like conches that sit comfortably inside the rib cage. Like a very long lung that’s coiled up like a python, except it’s one structure and can’t be straightened out. The trachea connects to both ends of the lungs for optimal airflow (because birds are unmatched in the breathing department). Aside from confusing the air molecules inside I’m not entirely certain what the advantage would be. My hypothesis is that air stays in the lungs longer this way in order to maximize gas exchange.

Tips for answerers: The method of respiration can be by compression or with air sacs circulating air through stiff lungs. Both versions should be explored in the answers to give a good idea of where they stand.

Answer 1

Countercurrent heat exchange

Not quite sure the exact kind of spiral you mean but if an organism needs to maintain a very different body temperature from the gas around it in an extreme environment and is otherwise well insulated then having incoming and outgoing gas spiral around each other through counterflowing passages might allow a stable temperature to be maintained.

For example penguins feet use something similar for blood to reduce heat loss through their feet in extremely cold environments.

Blood going one direction exchanges heat with blood going the other in a spiral.

You might try something similar with gases being breathed in and out.

Answer 2

A one-way air passage

When we (humans) inhale and exhale, the air enters the lungs and exits them through the same passage. So minimizing the distance to the trachea from any part of the lung is an energy-saving optimization in our lungs.

But if your organism has two different entries into the lung, this allows us to use valves to have a directed, one-way flow of air through the lung (even if both those entries connect to the same outside opening). Then their lung might be more similar to a human gut - a long tube, with complications along the inside to increase surface area. But our gut is way too long to fit in our body, so it's all coiled up - a similar adaptation with your one-way lung would seem likely.

Circulation via compression: If we want to contain the tube nicely inside an expanding/contracting muscle membrane, a spiral could be a convenient shape to pack it.

Circulation via "air sacs in stiff lungs": Not really much different--it's still advantageous to pack the lung tissue together; and the air sac(s) can simply be placed at one end or both.

An advantage of one-way airflow: countercurrent exchange

Countercurrent exchange is a well-known feature (already used in the lungs of birds, which you mentioned, and in fish's gills--with thanks to @Turksarama for pointing that out to me) that optimizes the transfer of gas (or heat, or chemicals dissolved in a liquid) across a membrane. For your one-way lung, this would mean you direct the flow of blood the around the lung in the opposite direction to the airflow.

Answer 3

What Qami said about one way passages, plus what Nyakouai said about increased gas exchange surface, but let me add one more thing: voice organs.

Your aliens might not have vocal cords like we do. Instead they vibrate different sections of the conch in order to speak. The larger the piece the deeper the voice. So an alien's vocal range depends on the sizes of their conch lungs, from the biggest cavity providing the lowest frequency to the smallest cavity giving the highest pitch.

This is very similar to how we humans perceive sound, by the way. We have an organ inside our ear called the Cochlea which is also a spiral (the emphasis below is mine):

The hair cells in the Organ of Corti are tuned to certain sound frequencies by way of their location in the cochlea, due to the degree of stiffness in the basilar membrane. This stiffness is due to, among other things, the thickness and width of the basilar membrane, which along the length of the cochlea is stiffest nearest its beginning at the oval window, where the stapes introduces the vibrations coming from the eardrum. Since its stiffness is high there, it allows only high-frequency vibrations to move the basilar membrane, and thus the hair cells. The farther a wave travels towards the cochlea's apex (the helicotrema), the less stiff the basilar membrane is; thus lower frequencies travel down the tube, and the less-stiff membrane is moved most easily by them where the reduced stiffness allows: that is, as the basilar membrane gets less and less stiff, waves slow down and it responds better to lower frequencies. In addition, in mammals, the cochlea is coiled, which has been shown to enhance low-frequency vibrations as they travel through the fluid-filled coil. This spatial arrangement of sound reception is referred to as tonotopy.

Answer 4

Extraction

First off, it is a nice idea, but not practical. The air is more difficult to push through the long winded pipes, costing more energy.

That out of the way, you can have super extraction. Lung lining is designed much like the intestines. It's made so there's a lot of surface area. The difference is that lungs are made to easily replace their gas with fresh oxigen holding particles that can swirl around a bit.

Your organisms have much more surface area for the lungs. That means more efficient oxygen extraction. This can change on what is needed. Either more quickly extraction, preventing the organism of using bad anaerobic processes in extended effort situations, or used to hold their breath longer. This last one won't be too much longer mind you.

Answer 5

What an alien idea. I like it.

I suppose your weird shape could somehow increase the total contact surface of your lungs, making them more efficient compared to boring old regular shaped lungs. There could also be more major blood vessels running in the coils of it, allowing for a quicker transfer of oxygen into vascular system.¹

Or (weird idea), it developped this way because your creature is somehow exposed on a regular basis to void. To avoid air being pulled out of the lungs, your coils are lined with sphincters that contracts and isolate sections of your lungs to create pockets of air.

_{1: Keep in mind, those are ideas from someone that hasn't had a biology class in the past 10 years.}

Answer 6

An internal cooling coil.

Building on Qami's idea of a one-way airway, a coil-shaped "lung" could also serve the purpose of cooling the body from the inside, in the same way a cooling coil would, by running a colder fluid through and around a warmer body or tube.

That might come in handy e.g. for large animals with active metabolisms that generate a lot of heat and have a low (skin) surface area to volume ratio. If a biological process like digestion or other metabolic functions produces a really strong exogenic thermal reaction, maybe the lung could loop around that area to cool it off. Having a one-way system with an 'in' and an 'out' would allow you to cool off continuously with no need to inhale.

Answer 7

Reality Check = FAIL!

The first important consideration for this kind of breathing system, the conchoid lung, I believe, will be dead space.

The other important consideration is that your system isn't set up and doesn't function like a bird's respiratory system.

So, what will happen? --- Dead space is the term for air that sits in a tube that can not be properly inhaled or exhaled. In other words, your chest cavity is only able to expand so much, so the amount of air inhaled is limited by the available chest volume. The more tubing you add to the system, the harder it will be to bring fresh air in and clear stale air. The air that gets into the very end of the lung will become stale and will be unlikely to clear.

In a human lung, the entire volume is taken up by increasingly smaller branches and then even tinier ones. So, the large trachea divides into two primary bronchi each of which divides further into a couple more levels of smaller secondary & tertiary bronchi. These in turn divide into many bronchioles which terminate in alveolar sacs where gas exchange happens. This works well because the distance from any one alveolus to the outside is relatively short and the respiratory cycle can fill and empty the lungs without (much) air remaining inside (there will always be some).

Your conchoidal lung basically presents us with a very long tube. The distance from the most proximal alveoli to the outside will be comparable to the distance of the alveoli in the upper lobes of the human lungs. However, the distance from the most distal alveoli to the outside might be a metre or more! That part of the lungs will be filled with dead air that will hardly ever be cleared.

You'll have to either scrap the conchoid lung or else scrap the relatively humanoid thoracic cavity you described. See below under reinventing the wheel.

Bird breathing is complex! --- Birds have two lungs, nine air sacs, and a four stroke respiratory cycle. Inspiration brings 1. the current breath's fresh air from outside into the posterior sacs and also 3. the previous breath's stale air from the lungs into the anterior air sacs. Exhalation pushes 2. the current breath's fresh air from the posterior sacs and into the lungs and also 4. pushes stale air from the previous breath back to the outside. The result is a continuous flow of air through the lungs.

The extra tubing coming off the distal ends of the conchoid lungs will not effect continuous breathing. In stead, they will just create more dead space.

Conclusion. --- As it stands, I think your system will both fail to produce a superior volume of air flow & gas exchange and also will defeat itself by taking up too much valuable space within the chest with extra tissue and dead space.

Lastly, if you just connect those extra tubes to air sacs, well, then all you've really done is reinvent the wheel that avian dinosaurs invented millions of years ago. The argument for increased surface area for gas exchange fails again. Whereas before, only the most proximal portions of the lungs would really receive fresh air; now, only the most distal parts of the lungs will receive fresh air. Much of the lung's coiled up length will just have stale air passing through it.

I think diminished returns on investment will eventually lead to smaller, more straight forward lungs.

Answer 8

A spiral-shaped lung could be good for separating out different-sized particles from the air that your creature inhales. The shallower curve at the outside of the spiral will allow smaller particles to flow around it, but the centrifugal force will push larger particles into the lining; and so on, as the curve gets sharper towards the centre of the spiral.

If your creatures live on a planet with lots of different kinds of dust, spores, and other particles which the creatures are adapted to inhale but which need to be filtered (e.g. maybe they eat the spores from the air but need to cough out the dust), then a spiral-shaped lung could function as a filter.

Answer 9

Two crazy ideas

1. For symbiosis: posit another creature which normally lives in spiral shapes (like a conch/shell) but sometimes found its way into the lungs where it supplied a symbiotic function like producing oxygen and helping the critter stay underwater longer, or filtering blood and converting waste product into useful product or less toxic waste product. Over time, critters develop spiral shapes in order to better acquire and accommodate the natural shape of their symbiotes, and over time critters have gotten used to having stuff live in their lungs.

2. For reproduction: if the lung cavity doubles as a reproductive cavity, then perhaps it has undergone an effect similar to the Earth-borne duck.

Answer 10

You said "air" but didn't really specify the composition of the atmosphere. If it was some sort of electrically-charged fluid, running it through spiral lungs would be useful for inducting electrical current. This could be a sort of "electrical respiration" for this species, rather than chemical respiration like we have.

This could also have the nice side effect of, when they go for a run or a bike ride, they could keep whatever they have that's analogous to cell phones in their pockets. Then by the time the exercise was over, they devices would be fully charged.

Answer 11

Gas chromatography

The air of your planet is far more complex than the atmosphere of Earth. A rich mix of hydrocarbons, silanes, germanes, amines and fluorinated compounds, it provides many useful chemical precursors. Unfortunately, your species' membranes, like ours, are lipid bilayers with little capacity to control which compounds cross, whether beneficial or baneful.

With the spiral lung, your organism breathes in a brief pulse of external air, followed by a carrier gas recycled internally from the absorbed inert compounds. This adheres differentially to the polysaccharide- and water-coated solid support phase of the spiral lung. After a moment, inhalation stops. This leaves each type of chemical having travelled a different distance depending on its hydrophilicity, and cells specialized to deal with each type of chemical constituent do so - whether to absorb, detoxify, or route through toward small channels for rapid "exhalation" from small ducted glands.

The system is not tremendously efficient as a means of respiration - I'm going to assume the primary means of absorbing oxidizing agents is by drinking compounds that rain down in the wind from the sunlit side of the planet, and that supplemental hydrocarbon intake is done by ordinary eating. But the breathing apparatus could deliver a wide range of useful trace elements from an otherwise hostile atmosphere.