The anus is an evolutionary marvel
theatlantic.com
theatlantic.com
Here's a fantastic (and free) book about just this structure:
I'm not an expert in, well, anything, so I rely a lot on Wikipedia for the basics.
You're right though, the engineering that goes into our bodily machines is mind boggling.
https://www.implantica.com/im-refluxstop/patients/gastrointe...
Who knows?
All I know is that it's different for everyone and for lots and lots of people, eating totally normal things is what causes or contributes to lots of bad symptoms misattributed to some disease or disorder. More often than not it's not you, it's the utter garbage food that our society has standardized upon. Just because it's common to eat a sandwich, or pasta, or a bowl of cereal or granola, or a bagel doesn't mean that human evolution has caught up with it yet.
I live on espresso/tea, heavy cream, protein/nutrition shakes, zero-cal flavor syrups, and grilled beef. It's sort of crazy how much healthier I am eating this than if I ate, say, even healthy sandwiches. My body just seems to dig being primarily a carnivore. If I personally liked vegetables and leafy greens more I would probably do vegan keto, as I don't like how unsustainable western meat production is, but I simply can't get into the idea of leafs as food.
Do you have an ELI5 for how this works?
But the vertical fists model helps to visualize the pylorus as a "cylinder" of annular muscle segments that contract and relax with alternating timing to pump liquid from the stomach into the duodenum in precise metered doses. This timed and coordinated squeezing action is called peristalsis, and is the mode of action of all your intestines as well as your esophagus.
Now here's the important part: notice that when you squeezed your top fist, liquid squirted out in both directions. Dynamic studies of the pylorus in action show that these two "squirts" are not the same. The forward squirt is usually smaller and contains only liquid and fine particles of food, whereas the larger backward squirt (called retropulsion) contains all of the large chunks of food that require further digestion.
So how does the pylorus do this? The answer lies largely in the shape and structure of the sphincter wall, and here's where it gets really crazy. The pyloric cylinder has two sets of muscles moving it: the big strong external rings of muscle, and a finer inner layer of muscle in the mucosal lining. When these muscles contract and relax, the inner mucosal lining forms various patterns of folds and wrinkles. When the pylorus is pumping liquid from the stomach to the small intestine, the two sets of muscles work together to shape folds and wrinkles that "grip" chunks of food, prevent them from passing, and then launch them backward, back into the stomach. The shapes of the folds is highly variable, and it appears that your pylorus adapts these intricate patterns in its lining from moment to moment based on the properties of the food in your stomach-- it's texture, viscosity, the shapes and sizes of the chunks in it, etc.
How does your stomach "know" these details about the food in it? I don't think anybody really knows yet.
In case anyone's looking for an exact source, here's the money quote from page 62 of the book:
> A certain contraction of the outer muscular tube is necessary for the formation of macroscopic mucosal folds. The variability of the fold pattern is also dependent on the hydrodynamic action of the fluid content of the submucosa, which in turn depends on the degree of filling of the blood vessels; the mass of mucous membrane, and consequently the volume of its folds, is regulated by the varying vascularity in the submucosa.
> In addition Forssell showed that the surface of the mucosa, or mucosal relief pattern, may vary from moment to moment; these movements are independent of, but co-ordinated with the contractions of the muscularis externa. Especially in the small intestine, but also in the stomach, various active contractile shapes, in some of which the mucosa "grips" particles of food, may be discerned. These consist of digestion chambers, blocking or filtering devices, re-absorption reservoirs and smooth or corrugated transporting tubes. In this way each region may best meet the varying demands placed on it from moment to moment, namely digestion, storage, absorption and transport respectively. One moment the mucosa may be occupied with one task, the next with another. Forsell called the inherent ability of the mucosa to move "mucosal autoplastik", providing a working relief pattern. It also determined to a large extent the number, position and form of the folds. While the coarser breakdown of food particles is effected by contractions of the muscularis externa, the finer dispersion occurs through changes in the relief pattern of the mucosa, which may enhance or counteract effects of contraction of the muscular walls. The special contractile organ of the mucous membrane is the muscularis mucosae; being attached to the mucosa and being incorporated in the submucosa, it is able to displace the former in different directions.
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EDIT
It's been almost twenty years since I read this book, and re-reading the quote above, I realize that this wild mechanism I described is also used in the small intestine (not just in the distal stomach and pylorus). It makes perfect sense, but it never occurred to me that this is how a whole lot of our guts work to move and process food. It's kind of another epiphany for me.
Anus inspired honey dispenser https://imgur.com/a/jmQUSYr
So here again, how does your stomach "know" when to stop trying to digest certain pieces of food and let them pass on to the small intestine? This topic is called gastric emptying, and it's a whole other rabbit trail. Your stomach monitors the chemistry of the food in it-- specifically, the chemistry of the digestion products generated as the food breaks down. It knows lots of details about the carbohydrate, protein, and fat being released, and it knows how quickly its digestive enzymes and acids are being used up. So it knows how much more work needs to be done, and whether or not its worth trying to get more nutrients out of a piece of unchewed nut, for example.
There are many other variables, and I think digestion is still largely shrouded in mystery. Studies have shown variation in gastric emptying rates based on the biological activity of food, infections in gut tissues (even if they're subclinical, i.e., you don't feel unwell), time of day, and even the person's emotional state. The guts are the seat of a large part of the autonomous nervous system, and science has barely scratched the surface of it.
Fun fact: I had pyloric stenosis as an infant. IIRC, this condition tends to hit first born males of which I am one.
Dearest mother kept bringing me into the hospital. "He keeps throwing up no matter what." She kept being told the "oh you're just a new mother" song until finally one doctor switched on a lightbulb to check something out.
Next thing is that I'm this infant on an adult stretcher being prep'd for surgery.
My oldest scar.
I swear if I was born 100 years earlier I'd be dead by starvation at no fault of anything but medical innovation.
In any case, congratulations on your continued survival!
For a few years, there was work related to the anus, which according to the staff was an under-studied topic for obvious reasons.
I'm afraid I chickened out of choosing the "model the anal sphincter" project. In retrospect it sounded fun and interesting.
The whole thing about human buttocks as well I recently learned about after getting a dog of my own (ya ya, covid puppy acquirer here). I was always weirded out by my childhood dog's butt and read up on it while I was researching dog ownership before I got my current little buddy. I figured I was going to have to wipe his butt to ease my slight-yet-ever-present faecal phobia. I then learned that dogs (and most mammals) actually prolapse pretty extremely when pooping, making it so that poop rarely touches their butts (at least on short haired dogs). As it turns out, my pup's butt is generally the least smelly part of him!
Anyway, a bit of a ramble about a dog's butt that many probably already know, but(t) I found it fascinating.
I'm not trying to convince you to get a dog or anything, but I never wanted one and it completely changed my life in so many positive ways. I'm getting outside regularly, I've made new friends, I've developed acquaintanceships with several awesome people in my neighbour, I talk to strangers, and my weekends now have structure which has made me incredibly productive in my personal projects--I now view the downtime I have between walks and general caretaking of my pup as very precious and not to be wasted whereas before I could spend an entire Saturday in bed if I felt like it.
(ya, I said embarking... I know what I did)
I and my family have had lots of dogs over the decades, and, looking back, the poodles have been my favorites. My present dog is a standard poodle who exemplifies what I like about the breed. She's smart, polite, curious, friendly, playful, and compliant. Smart and compliant in particular don't always go together in dogs, and it's a real bonus when they do.
Molly loves everyone, and is always happy to meet new people and other animals. She is nevertheless a good watchdog, who feels it's her duty to inform us if anyone (human or otherwise) approaches the property. On the other hand, as soon as we acknowledge her alerts, she stops them, which means they don't become tedious.
Poodles are retrievers, which may account for her tendency to bring me small animals, always completely unharmed, and to come and get me when she finds injured or dead animals near our house. Some birds and squirrels owe their continued lives to Molly.
There are a great many such things, such as that skeletal remains of old civilizations showing very good teeth for civilizations wherein the brushing thereof was nonexistent, but the diet contained no added sugars.
A rare and treasured occurrence indeed.
Squatting, as you would do outdoors if you didn't have a toilet, spreads the buttocks and there is much less cleaning needed. It also promotes more complete emptying so you don't have fecal matter left "pinched" in the anus that needs to be wiped up. If you use a typical western toilet, get something like a Squatty Potty to prop up your feet and you'll find you need to do much less wiping.
In the West I have to go through meetings knowing how unclean everyone's bottoms are /s
The mind boggles at how you've determined this...
But indeed the digestive tract is what makes us tori and not spheres.
Depending on pup, you can easily get a bunch of body parts shoved into smelling distance without any effort other than continuing to be alive. Then it's just a matter of recall and forming an opinion.
Hopefully this isn't TMI and in the spirit of this article!
I have a lot of dogs. Every once in a while, it seems that one of them gets a plugged up anal gland, or it doesn't get fully expressed when they poop. An earlier commenter said to look for liquid dropping out when they poop; I see this all the time. But sometimes that doesn't work for whatever reason, and then later on the gland "pops" and all the stuff comes out. The dog is usually sitting on my lap when this happens. It happens with both girl and boy dogs. My wife calls it getting butt-juiced.
The smell causes me to immediately change my clothes. It's not a fecal smell. I can't begin to describe it, but once you smell it you'll never forget.
Years ago we fostered a girl dachshund who loved my wife but hated me and feared me like the devil himself. Often when I would approach her in any but the slowest and most non-threatening way, she would tense violently and squirt anal gland juice like a skunk. Sometimes she'd leave a trail of the stuff on the floor as she ran for her life. One whiff would tell you it wasn't urine.
(BTW, that poor girl dog was eventually adopted by a sweet single woman and they are now inseperable companions)
I'm sorry to put this in your head but... fish sauce.
Source: I heard it from a vet.
Obviously my pug's butt has some kind of smell because all the other dogs keep smelling it :D My complacence is more with that if he sits his butt down on my pillow, I'm not going to freak out about it. Should I be concerned about this?
The uneven distribution is that not all dogs do it naturally, some need occasional assistance (you can do it but I’d recommend a quick/cheap vet visit, it’s gross and a bit of finesse). Some dogs just don’t get it done naturally and need that assistance on a regular cadence.
The health implication besides being a natural bodily process is that if it backs up, the whole solid waste system backs up.
Edit: don’t be overly worried, but do be attentive. If you see butt scooting this is probably what’s going on. (If it’s not it might be something more serious like a tapeworm. But I doubt that from what you described.)
And dogs are very attuned to the scent. If you smell it too it’s probably a good idea to go let a vet nurse squeeze out your pup’s anal glands. It’ll be a relief for pup and not at all traumatic.
I've seen videos on youtube of people expressing a dog's anal glands, but I myself have never once been able to do it. There must be a special technique that I just can't get.
There is definitely a technique, but for $5 or $10 extra at the grooming appointment I think I can afford to go a while longer yet before I try to figure it out for myself - I mean, I know you can go on YouTube and learn pretty much anything but I just can't see myself...
Clearly not, since it's not really feasible to give birth without simultaneously defecating all over the place. One of more unpalatable secrets kept from men back in the era where you were supposed to just sit in a different room and smoke your cigar.
P.S. also enemas were used in the past... but fortunately, interventions such as this, or pubic hair shaving are no longer ordered for women during labor and birth!
Congratulations my man.
Anus inspired honey dispenser https://imgur.com/a/jmQUSYr
ānus = ring / anus
annus = year
anus = old woman
Ano means anus, while año means year.
One of the first sentences a student of Spanish will learn is "¿cuántos años tienes?", how old are you, literally "how many years do you have?"— often before they really grasp the distinction between ene and eñe.
And indeed I see this on etymonline:
> from Latin nucleus "kernel," from nucula "little nut," diminutive of nux (genitive nucis) "nut,"
So for whatever reason a new word was called for, and our nucleus comes from that, not from the diminutive form of "nut".
I've been wondering about this! Does Spanish regularly form diminutives other than with the -it- infix? ("m'hijito" etc.) Latin forms them with -ill-, -cul-, or -ul-, and many such forms are obvious in Spanish (tomatillo / quesadilla etc.), but I've never known whether -ill- is still productive today or if those are relics from the past.
It's fun to see a Spanish region bordering Portugal (-inho) forming diminutives with -iño and one bordering France (-ette) forming them with -ete.
That’s a result of medieval hymn writers. They would write conception/gestation/birth related hymns to the Blessed Virgin. They used an a strict rhyme scheme.
So lots of of medieval monks had to ask “What’s a term for uterus that rhymes with tempora? Ok how about viscera [intestines]? Viscera it is.” And the hymn becomes popular so now viscera means uterus or breast or something.
Of course most will die at first. But that's a price evolution is always willing to pay.
Regardless, I am now picturing a future where evolved humans find the smell of plastic appetizing.
Do our primate cousins in the forests and zoos get hemorroids?
What's changed is that people don't die as infants anymore.
It also doesn't make sense: vaccines and antibiotics don't just protect infants.
> The modern Amish also don't currently live in a society with endemic smallpox.
That's why I said access to doctors, not to public health, which is what's kept most of us alive. Though I don't know how modern their approach to childbirth is, that one's important.
One interesting data point is that the age at which people transition economically from accumulating wealth to transferring it has remained about the same (around 64), at least as far as Western European inheritance records prior to demographic transition show. Ie. people retire at the same age. They just spend more time being old. I'm not sure it's all that much progress. I wish we found ways of making people useful longer, rather than just trying to keep them from dying.
This means that our actual durability and lifespan hasn't improved that much, just our ability to fix and avoid previously fatal injuries.
If humans weren't genetically encoded to die from old age, vs just plain wear and tear like you would with a car, you would statistically see a small amount of humans who lived until 300 today. Just like how there are thousand year old well preserved physical objects today.
"Takanori - One is a very intuitive approach we just intubated, from the anus, just to provide oxygen gas continuously. This oxygen delivery is really able to persist survival in lethal conditions. Even up to 60 minutes or even longer.
Eva - 60 minutes of breathing through the rectum just by pumping in oxygen. Sounds amazing, but also like you could get a bit uncomfortable. The more clinically relevant approach uses a liquid that's very good at dissolving oxygen, perfluorocarbon or PFC. This liquid is already used by doctors during some ice surgeries and sometimes as a type of synthetic blood for transfusions. So we already know that it's safe for humans.
Takanori - So that liquid ventilation approach is also having greater impacts on oxygenation. So as to really rescue those fatal hypoxic conditions in the mouse, rats, and pig model system.
Eva - Incredibly, Takanori showed that when just less than a pint of this PFC was injected into the anus of pigs, they would stay happily oxygenated for up to 20 minutes when in respiratory failure. And they didn't stop there, by re-injecting every 20 minutes or so they could keep the pigs going for hours, or even more. Importantly though, when we breathe in and out using our lungs, we aren't just taking in oxygen. We're getting rid of carbon dioxide and other waste products too."
Transcript of interview: https://www.thenakedscientists.com/articles/interviews/intes...
NY Times article: https://www.nytimes.com/2021/05/14/science/rectum-breathing-...
//EDIT//Actual paper: https://www.cell.com/med/fulltext/S2666-6340(21)00153-7?utm_...
Evolution sucks.
I see the domain is now available.
How about this design where you stuff food in the same hole you breathe through?
Seems so unnecessarily dangerous.
I agree, but it hasn't killed enough to evolutionarily matter.
It's not like there's no mitigation in place in the body itself.
Evolution's solution: cough it out
Better solution: don't send food, water, and air down the same pipe in the first place
I mean, no competent engineer would design the plumbing for a building such that the same pipes were used for water and air at different times, right?
> All amphibians, reptiles, birds, and a few mammals have this orifice, from which they excrete both urine and feces.
> Mating through the cloaca is known as cloacal copulation, commonly referred to as cloacal kiss.
> The cloacal region is also often associated with a secretory organ, the cloacal gland, which has been implicated in the scent-marking behavior of some reptiles, marsupials, amphibians, and monotremes.
"In every final scan we could see a big, full bladder, even though most of the women went to the toilet before they went inside the MRI,” explains Pek with comical astonishment. “We think it might be evolution’s way to force women to urinate after sex. Perhaps our ancestors developed this function to avoid urinary tract infections, but that’s only a hypothesis."
https://www.vice.com/en/article/qvgkzw/the-story-of-the-dutc...
> We have very little idea where anuses come from
This also more accurately describes what the article is about.
Problem: Warm-bloodedness means the testicles are now too warm to work well.
Hack #1: Hang them on the outside of the body so they can stay cooler.
New problem resulting from first hack: Now they're much easier to damage.
Hack #2: Make them hurt really bad if they get bashed, so the owner takes great care to guard them.
The proper solution would have to make them more temperature-tolerant in the first place.
Interestingly, ovaries didn't go down this road, though there are certainly some suboptimal designs in that whole system as well.
A fixed quantity of viable eggs within prime child bearing years until menopause when women would then perform other roles within the community.
I prefer Stephen Jay Gould's point that lots of evolved subsystems are just kludges and jury-rigged solutions that just happen to work good enough, sort of. ("The Panda's Thumb").
(That 13-year-old me read at the time when I stumbled across it in my grandfather's study.)
https://www.youtube.com/watch?v=0VyH1laOd2M good video on this
Rectal Breathing with Perfluorocarbons (cell.com) https://news.ycombinator.com/item?id=27159001
The Anus: Judge skeptical that Holmes’ luxury lifestyle should go before jury
If your workplace would fire you for the title, you should strongly consider finding a new workplace.
"Butts: finding the source."
or:
"Scientists Find That Hindsight is not 20/20"
https://en.wikipedia.org/wiki/Embryological_origins_of_the_m...
Ontogeny recapitulates phylogeny was somewhat debunked even 150 years ago. I speak as someone who owns a dozen Ernst Haeckel first or early editions.
Is there some related underlying concept we can't put our finger on? Maybe. Just like Dunbar's number
Our embryo though passes through the stages which were inherited from the embryos of our more primitive ancestors - the "embryo tree" structurally parallels and mirrors the evolution tree.
What's the correct pronunciation?
Pretty much everything that has evolved is intricate in ways we can’t even understand. When everything is a marvel equally, nothing is. But it’s not equal. Some things are more marvelous. So we call them a marvel. It’s how words work.
Say, a green ball is also technically a red ball and blue ball. Nothing is perfectly green. But you still don’t call a brightly green ball a red ball. Because that’s how words work.
Also, sphincters and valves have evolved countless ways independently in living organisms (and even in structures they build), and they're omnipresent also in the machines we create.
Regulating flow in a pipeline (of any kind) is possibly one of the most basic adaptations you need in order to make a working system... of anything.
So in fact... sphincters ARE completely ordinary and expected, if you ask me. And the anus is not special relative to other sphincters (and despite The Atlantic trying to be cute about it, they really don't support their headline in the article either).
While this comment may draw unhelpful and undesired debate, I genuinely believe these amazing structures were created by the Word of the Almighty God and credit should be given where it is due. These are incredible designs by our omnipotent creator.
If credit should be given where credit is due, should we also be allowed to criticize where the design is not amazing?
Why would we mere mortals be capable of knowing good design when we see it in the first place?
The dynamic range is quite good though.
Apart from that, all the evidence is actually on the side of the Christians, even though it's all anecdotal: scripture, patristic documents, traditions, etc. It's not quite enough to convince me, but the other side has exactly nothing, not even anecdotal evidence, on why there is something rather than nothing.