Speaker 1: Welcome to Stuff to Blow Your Mind, a production of
Speaker 1: My Heart Radio. Hello, and welcome to Stuff to Blow
Speaker 1: Your Mind Listener Mail. I am Joe McCormick, and my
Speaker 1: regular co host Robert Lamb is off work the weekend
Speaker 1: recording this, So like last Monday, I'm gonna be recording
Speaker 1: another listener Mail episode, so low but never fear. Rob
Speaker 1: will be rejoining me and we'll have some fresh new
Speaker 1: episodes for you sometime later this week. But for today,
Speaker 1: I'm going to dive right into a few of the
Speaker 1: messages that you've sent in over the past cycle. Looks
Speaker 1: like this. First one comes from Chris. Chris says, hey, guys,
Speaker 1: love the show. Something that blew my mind recently has
Speaker 1: to do with evolution. Here it goes in the ancient
Speaker 1: timeline of life on Earth, sharks are older than trees.
Speaker 1: I always thought of plants as first. Knowing that sharks
Speaker 1: were swimming around for a hundred million years before there
Speaker 1: were even trees blew my mind. Thanks Chris, Chris. Yeah,
Speaker 1: I I love stuff like this. So to fill in
Speaker 1: some detail on this claim, I would say that this
Speaker 1: statement is true, though it depends a little bit on
Speaker 1: how strict your definitions of a shark are um there
Speaker 1: there's some debate, I guess, about what counts as evidence
Speaker 1: of the first shark. But for reference, I just looked
Speaker 1: up the timeline summarized by the Natural History Museum of London,
Speaker 1: and according to them, there are a few fossil scales
Speaker 1: that appear to come from shark like animals, dating all
Speaker 1: the way back to the Ordovician period, So that's four
Speaker 1: hundred and fifty million years ago, which is mind bogglingly old.
Speaker 1: The Ortivician is the first geologic period after the Cambrian,
Speaker 1: and if you remember, we've done episodes on this in
Speaker 1: the past, the Cambrian is when we first see the
Speaker 1: explosion in divers city of animal body plans, animal body
Speaker 1: plans with hard parts that leave fossil traces, and so
Speaker 1: this is the age of the triobytes, of course famously,
Speaker 1: but also these these amazing creatures like Anomala carress, this undulating,
Speaker 1: soft bodied predator with a ring shaped crusher mouth and
Speaker 1: little face tentacles that look like shrimp anomal a caress
Speaker 1: actually means anomalous shrimp or weird shrimp. And uh creatures
Speaker 1: like Hallucigenia, which is the wandering spike worm. Uh and
Speaker 1: so so that's the Cambrian. But then after that we
Speaker 1: enter the Ordovician period and there we yes, we do
Speaker 1: see evidence of scales, but not teeth. But the scales
Speaker 1: look like they may have belonged to some kind of
Speaker 1: ancestral shark or creature that that overtime became sharks. So
Speaker 1: that evidence is is a maybe. But then by the
Speaker 1: early Devonian period, about four and ten million years ago,
Speaker 1: there is clear fossil evidence of shark teeth from a
Speaker 1: fish called Dolotas problematicus, which was beginning to show some
Speaker 1: of the signs of shark like anatomy, such as in
Speaker 1: the teeth and the jaw. And there's another early shark
Speaker 1: from the Devonian that I was reading about that I
Speaker 1: think we don't know much about, but it's called Leonotas
Speaker 1: l e O n O d u s. And the
Speaker 1: the only thing that I could really find about this
Speaker 1: one had to do with its teeth. If you get
Speaker 1: a chance, you should look up the teeth of the
Speaker 1: Leonoda shark. These creatures were about four million years old,
Speaker 1: and its teeth are not the serrated triangles or or
Speaker 1: the murder spikes you might think of in in shark
Speaker 1: mouth today. These look like well they look like the
Speaker 1: devil horns. They look like somebody in a metal show
Speaker 1: they go, they throw up the devil horns. They're these
Speaker 1: little y shaped forks, which makes me wonder what kind
Speaker 1: of prey this animal was eating. What do you bite
Speaker 1: with a bunch of little spiky, y shaped forks? I
Speaker 1: don't know. But meanwhile, the evolution of trees is also
Speaker 1: an interesting subject. I think the first things we would
Speaker 1: identify as trees, meaning tall vascular plants on dry land
Speaker 1: with woody stems. These show up I think in the
Speaker 1: mid to late Devonian period, so maybe around three hundred
Speaker 1: ninety to three hundred and eighty million years ago, somewhere
Speaker 1: in that range. And in fact, the proliferation of land plants,
Speaker 1: including trees during the mid to late Devonian is one
Speaker 1: of the hypothesized causes of the big mass extinction event
Speaker 1: that happened at the end of the Devonian period. Now,
Speaker 1: of course, this is not a settled issue. There are
Speaker 1: a bunch of different ideas about what could have caused it. Uh,
Speaker 1: you know, you have the regular culprits, things like US
Speaker 1: impacts from space or a massive volcanic eruptions. Um. But
Speaker 1: at least one idea that has been advanced is that
Speaker 1: as the continents were covered in plants and forests during
Speaker 1: the Devonian and as as the land turn green, suddenly
Speaker 1: a large amount of the carbon in the atmosphere was removed.
Speaker 1: Because remember this really weird fact. Plants the parts of
Speaker 1: plants that is not water, that is mostly built out
Speaker 1: of atoms that were originally in the air. So carbon,
Speaker 1: the carbon in wood in a tree trunk comes from
Speaker 1: atmospheric c O two that plants ingest and then they
Speaker 1: use the energy from sunlight to power the chemical reaction
Speaker 1: uh we know as photosynthesis, So it reacts CEO two
Speaker 1: with water to produce carbohydrates and oxygen as a byproduct.
Speaker 1: So you have the proliferation of forests that might have
Speaker 1: removed a bunch of carbon from the atmosphere to cause
Speaker 1: a sort of anti greenhouse effect leading to deadly rapid cooling.
Speaker 1: But again, there are other possible explanations for the for
Speaker 1: the late Devonian extinctions, so we don't really know for sure. However,
Speaker 1: one last cool thing to notice when you put sharks
Speaker 1: and trees side by side, so it does look like
Speaker 1: the sharks came first. But the other thing to notice
Speaker 1: is that they both appear to have had a sort
Speaker 1: of flourishing age of diversification and dominance in the period
Speaker 1: right after the Devonian, which is known as the Carboniferous
Speaker 1: So the Carboniferous period lasted from roughly three hundred and
Speaker 1: sixty to about three hundred million years ago, and it
Speaker 1: is named after the fact that this is the geologic
Speaker 1: strata that we first find packed with lots of coal.
Speaker 1: Carboniferous means coal carrying or full of coal, and coal
Speaker 1: is of course a form of fossil carbon that came
Speaker 1: largely from dead plant matter, including trees, especially trees that
Speaker 1: grew in low lying wetlands and swamps. So in these
Speaker 1: vast uh you know, continents full of low lying wetlands
Speaker 1: and wet forests and swamps, you'd have plants dying they
Speaker 1: fall down there there, or carbon content it's fossilized into coal,
Speaker 1: and then of course in the industrial revolution we we
Speaker 1: dig that up and that that turns into the energy
Speaker 1: that powers the development of modern civilization. But the Carboniferous
Speaker 1: period is also sometimes called the Golden Age of sharks.
Speaker 1: That same article I was looking at by the by
Speaker 1: the London Natural History Museum referred to it as the
Speaker 1: Golden Age of sharks. There's a great question why did
Speaker 1: sharks thrive in this period? Why this great diversification of sharks?
Speaker 1: And that's not known for sure. But one idea that
Speaker 1: I was reading at a great website called Elasmo research
Speaker 1: dot org. That's a shark science website that I think
Speaker 1: is mostly or entirely authored by a marine biologist named
Speaker 1: our Aiden Martin. I was reading on that site the
Speaker 1: idea that possibly sharks thrived in this period because at
Speaker 1: the at the Late Devonian extinction, another group of marine
Speaker 1: predators called the plaquaderms were wiped out. The plaqueoderms, if
Speaker 1: you've never seen pictures of them, you should definitely look
Speaker 1: them up there. They're great. They were armored fishes fish
Speaker 1: fish you would see with like plates around their head
Speaker 1: and sort of plate like jaws and mouths. Uh So,
Speaker 1: one good one to look up is called dunk Leosteus
Speaker 1: d U N K l e O S t e
Speaker 1: U S. Dunk Leosteus. And if you can find an
Speaker 1: image with a human for scale, or even better, if
Speaker 1: you can stand next to an arrangement of their armored
Speaker 1: head plates in a museum. It's a nightmare. You know.
Speaker 1: I would much rather face down a great white shark
Speaker 1: or I don't know, maybe even a megalodon. Is something
Speaker 1: about it's it's it's terrifying and awesome. But but the
Speaker 1: idea is that maybe with the competition of these plaqueoderms
Speaker 1: gone because they were wiped out at the end of
Speaker 1: the Devonian, maybe then sharks could expand and fill new
Speaker 1: niches and diversify. So anyway, thanks for kicking this off, Chris,
Speaker 1: but I wanted to give you an another one. So, yes,
Speaker 1: it appears sharks are older than trees. But did you
Speaker 1: know that mammals are older than bees. As with the
Speaker 1: previous case, there's some debate about where where you should start,
Speaker 1: you know what, at what point on the lineage you
Speaker 1: should say, okay, now these are mammals, because of course
Speaker 1: mammals are part of a lineage going back to the
Speaker 1: synapsids that lived even before the dinosaurs, you know, the
Speaker 1: dimetrodon So again you could debate about the where the
Speaker 1: best place to put their beginning is. But small furry
Speaker 1: sort of rodent ish critters that we would probably recognize
Speaker 1: as mammals existed during the reign of dinosaurs, with a
Speaker 1: number of fossils from the Jurassic Period between about a
Speaker 1: hundred and fifty and two hundred million years ago. Meanwhile,
Speaker 1: bees pop up later I think closer to a hundred
Speaker 1: and thirty million years ago. Anyway, thank you, Chris. Okay,
Speaker 1: this next message comes from Steven and it's in Risk
Speaker 1: wants to the series we did on thirst. Steven says,
Speaker 1: Dear Joe and Rob. As a recent microbiology graduate, I
Speaker 1: was delighted when you started talking about rabies, the horse
Speaker 1: hair worm and their relationships with their hosts thirst, and
Speaker 1: I remember that this was in the context of us
Speaker 1: talking about ways that UH disease causing pathogens and parasites
Speaker 1: will alter the host behavior in order to help themselves
Speaker 1: spread or reach another part of their their life cycle.
Speaker 1: So in the same way that a respiratory infection will
Speaker 1: make you cough and sneeze and spit more of the
Speaker 1: germs onto other people to to to spread it around faster,
Speaker 1: the rabies virus causes a series of behavioral modifications that
Speaker 1: that help it spread through bite. So you get bitten
Speaker 1: by an animal with rabies um and the the infected
Speaker 1: saliva put some of the virus into your muscle tissue,
Speaker 1: it spreads to the nervous system. Uh that that is
Speaker 1: facilitated by the fact that rabies tends to cause a
Speaker 1: kind of confusion, irritability aggression in its later stages, and
Speaker 1: that it makes it hard for the host to swallow,
Speaker 1: so it can't the The person or animal that's infected
Speaker 1: has difficulty or even finds it impossible to drink water,
Speaker 1: un thus can't wash all this infectious saliva out of
Speaker 1: its mouth, so each bite is supercharged as a vector
Speaker 1: of new infection. But Steven goes on to say, I
Speaker 1: thought I would add to the conversation with another interesting
Speaker 1: parasite that hijacks our need for water. The guinea worm
Speaker 1: is a parasitic worm whose life cycle depends on close
Speaker 1: proximity to water. As larvae, they spend their developmental years
Speaker 1: in the stomachs of aquatic copa pods that try to
Speaker 1: eat them. It isn't until they're consumed by larger animals
Speaker 1: e g. Humans that they can bust through our stomach
Speaker 1: lining and develop into adulthood while taking residents just under
Speaker 1: our skin. However, once the alt worm has set up
Speaker 1: camp under our skin. How does it get larvae back
Speaker 1: out into the world to begin the cycle again? If
Speaker 1: I remember correctly, the best cure for this disease is
Speaker 1: a simple stick with a notch at the end. The
Speaker 1: worm's tail is inserted in the notch and spooled out
Speaker 1: of the patient, much like a noodle being twirled into
Speaker 1: a fork. Of course, one can use a coffee filter
Speaker 1: to remove copa pods from drinking water, preventing infection altogether.
Speaker 1: Thanks for making such an informative and entertaining podcast. Sincerely,
Speaker 1: Stephen PS. Rob is right. Rabies is effectively one fatal
Speaker 1: if not vaccinated against before symptoms come on. However, there
Speaker 1: is one case of rabies being cured by a procedure
Speaker 1: called the Milwaukee Protocol. It seemed to have been a fluke, though,
Speaker 1: but it's an interesting enough topic to read about when
Speaker 1: you get the time. Well, Stephen, thank you for the message.
Speaker 1: Actually did look into this into the Milwaukee Protocol, and
Speaker 1: I found an explanation in a paper called Failure of
Speaker 1: the Milwaukee Protocol and a Child with Rabies, published in
Speaker 1: Clinical Infectious Diseases in two thousand eleven by Angela Arum Burrow.
Speaker 1: At all. So this paper is looking at rabies encephalitis,
Speaker 1: and this is the phase of Raby's infection where the
Speaker 1: virus has reached the central nervous system. Now, remember the
Speaker 1: normal courses that you're probably bitten by an infected animals,
Speaker 1: say somewhere in the body, maybe on the hand, and
Speaker 1: then viral particles from the saliva of that animal get
Speaker 1: into your muscle tissue, they infect nerve cells, and then
Speaker 1: they climb gradually up the nerve pathways until they finally
Speaker 1: reached the spinal cord in the brain. Now, remember that
Speaker 1: Rabies typically has a long incubation period. There can potentially
Speaker 1: be months between the initial exposure and the onset of
Speaker 1: symptoms with encephalitis. Rabies encephalitis may in fact be one
Speaker 1: of the worst and most deadly diseases you could imagine,
Speaker 1: and but it is pretty much entirely preventable if you
Speaker 1: seek treatment immediately after you get bitten or otherwise exposed.
Speaker 1: And the treatment is referred to in the literature as
Speaker 1: post exposure prophylaxis or PEP. And in fact, we've got
Speaker 1: some more listener mail coming up in a bit with
Speaker 1: direct experience with PEP. But anyway, the authors of this
Speaker 1: paper from two thousand eleven right that before two thousand four,
Speaker 1: there were only five documented cases of anyone ever surviving
Speaker 1: rabies and sephalitis, and all five of them were people
Speaker 1: who received some form of PEP, though they ended up
Speaker 1: reaching the encephalitis phase because the prophylaxis was maybe incomplete
Speaker 1: or late. But in the year two thousand four, some
Speaker 1: doctors reported the first ever survival of rabies and sephalitis
Speaker 1: without any PEP. This was in a child who had
Speaker 1: received what they called the Milwaukee Protocol, which is a
Speaker 1: combination h that they describe the following way. They say,
Speaker 1: it's quote therapeutic coma, anti viral therapy, cerebral vaseo spasm management,
Speaker 1: and avoidance of immunization. Now, unfortunately, it looks to me
Speaker 1: like attempts to reproduce this outcome in other patients have
Speaker 1: all failed, including in the case documented in this two
Speaker 1: thousand eleven paper. They tried the Milwaukee protocol, it didn't work.
Speaker 1: So it's possible that, as Stephen says, the time it
Speaker 1: looked like it worked in two thousand four, was some
Speaker 1: kind of outlier or some kind of fluke and and
Speaker 1: not a demonstration of any underlying usefulness in the therapy
Speaker 1: um and I've actually seen at least one more recent
Speaker 1: paper just discouraging its use altogether. We've got another message
Speaker 1: from Nate concerning treatment for rabies, and it goes like this,
Speaker 1: Robert and Joe love the show. I was listening to
Speaker 1: your episodes on Thurst and thought i'd share my experience
Speaker 1: with the rabies vaccine. Back in I had contact with
Speaker 1: a bat that found its way into my condo. I
Speaker 1: got it out of my place and wasn't too worried
Speaker 1: about it until my friend described how terrible rabies really is.
Speaker 1: I'm relatively certain that I wasn't bitten, but I went
Speaker 1: to the doctor anyway. The doctor decided to give me
Speaker 1: the vaccine to be cautious. The vaccine consisted of one
Speaker 1: shot in each arm and one shot in each thigh,
Speaker 1: followed by three more follow up visits with one shot
Speaker 1: in the arm. The first few days after the initial dose,
Speaker 1: I started to feel some flu like symptoms. Flu like
Speaker 1: symptoms also happened to be the early signs of rabies.
Speaker 1: At that time, I wasn't aware that vaccine side effects
Speaker 1: are relatively common, so that resulted in a pretty stressful
Speaker 1: couple of days. However, after the side effects went away,
Speaker 1: everything was good. Then my bill arrived for the vaccine.
Speaker 1: The pre insurance cost listed on the bill was thirty
Speaker 1: seven thousand dollars. It was so unbelievable that seven shots
Speaker 1: could be listed anywhere near that price. Luckily, my insurance
Speaker 1: covered most of it, but I still ended up paying
Speaker 1: about sevent dollars for the vaccines. I'm sure this pales
Speaker 1: in comparison with some other drugs, such as treatments for
Speaker 1: cancer and HIV and so forth, but it was pretty
Speaker 1: mind blowing how expensive it was. It's not the wildest story,
Speaker 1: but just thought i'd share. You guys have a great show.
Speaker 1: Thanks for all the entertainment over the last few years. Nate, Well, Nate,
Speaker 1: I'm I'm glad to hear you all right now. I'm
Speaker 1: I'm very glad in any case, that you didn't get
Speaker 1: rabies and cephalitis and uh. And obviously it's good that
Speaker 1: you had health insurance, but that that is an astonishing bill.
Speaker 1: I actually looked into this topic a bit, and I
Speaker 1: found an article exploring exactly this question, like why is
Speaker 1: rabies prophylaxis so expensive and why does the cost of
Speaker 1: it very so much so. This was an article called
Speaker 1: why a simple life saving raby shot can cost ten
Speaker 1: thousand dollars in America published in vox In by the
Speaker 1: healthcare reporter Sarah Cliff. I think she's at the New
Speaker 1: York Times now, but I've read a number of her
Speaker 1: articles about health healthcare in the US and uh and
Speaker 1: they're good. But in this article, so the background is
Speaker 1: that apparently there are just a lot of cases in
Speaker 1: the US where people end up in medical debt after
Speaker 1: a possible rabies exposure. And the article starts with the
Speaker 1: story of a college student who literally had a bat
Speaker 1: fly into her mouth while she was trying to shoot
Speaker 1: it out of her apartment. Uh. So she goes to
Speaker 1: an urgent care and there they describes what happened. They
Speaker 1: refer her to an emergency room for treatment. This was
Speaker 1: somewhere in New Hampshire. And then in the end, the
Speaker 1: bills she got for the full treatment was over six
Speaker 1: thousand dollars. And somehow this is on the low end
Speaker 1: of the cost range for for rabies p EP in
Speaker 1: the United States. The article claims that many bills are
Speaker 1: in the range of ten thousand dollars which of course
Speaker 1: is enormous, but obviously nowhere near your UH pre insurance
Speaker 1: bill of thirty seven thousands. So I really don't know
Speaker 1: what makes the difference in your case, especially since US
Speaker 1: healthcare costs are often rather opaque UM. But according to Cliff,
Speaker 1: the main itemized cost of these treatments is usually a
Speaker 1: drug called immunoglobulin, which is designed to slow the spread
Speaker 1: of the rabies virus in its progression towards the central
Speaker 1: nervous system, which gives the body time to learn from
Speaker 1: the vaccine and fight the infection. And UH immunoglobulin is
Speaker 1: allegedly expensive to produce because it has to be manufactured
Speaker 1: using human blood, which has to be pre screened for disease.
Speaker 1: So I guess it's a complicated process. But there are
Speaker 1: other major expenses for rabies treatment, sometimes because you have
Speaker 1: to go for multiple follow up visits and so there
Speaker 1: can be these hospital facility fees which get charged to
Speaker 1: people for showing up in the emergency room or at
Speaker 1: the clinic multiple times. But based on what this article
Speaker 1: describes it, it just seems like, you know, it's a
Speaker 1: say situation where the patient is kind of in a bind,
Speaker 1: like if you have potentially been exposed to rabies, you
Speaker 1: have to get the treatment. You really need these vaccines
Speaker 1: because they're extremely effective and untreated rabies is basically a
Speaker 1: hundred percent fatal, so you can't afford to just roll
Speaker 1: the dice and hope you won't get it. Uh. So
Speaker 1: it seems like drug manufacturers here have a lot of
Speaker 1: leeway in what they can charge and still sell plenty
Speaker 1: of the drugs. So apparently the same drug can have
Speaker 1: wildly different prices depending on where you get it. Cliffs
Speaker 1: article compares costs of identical rabies drugs in the US
Speaker 1: and other countries, and the ones in the US are
Speaker 1: sometimes like six times more than what the same drug
Speaker 1: costs in the UK. Though obviously in the UK, uh,
Speaker 1: there's another difference, which is the government will cover the
Speaker 1: direct cost to the drug rather than the patient. Um.
Speaker 1: But anyway, to come back on this, though, that is
Speaker 1: a pretty unpleasant state of affairs that you can end
Speaker 1: up with like a ten thousand dollar bill there. Uh,
Speaker 1: you shouldn't let that discourage you from seeking treatment if
Speaker 1: you think you might have been exposed to rabies, because again,
Speaker 1: untreated rabies always ends in death, and it's a horrible death.
Speaker 1: So if you think it's possible, you've got to get
Speaker 1: to a doctor as soon as you can. But anyway,
Speaker 1: this whole story reminded me of something else I was
Speaker 1: reading about recently, which is a totally different but complementary
Speaker 1: approach to fighting the impact of rabies on on on
Speaker 1: human society. And this intervention is attempting to intervene before
Speaker 1: infection occurs by vaccinating wild animals against rabies. So in
Speaker 1: the United States, most people who are exposed to the
Speaker 1: rabies virus apparently get it from domestic animals like cats
Speaker 1: and dogs, which in turn get infected through encounters with
Speaker 1: wild animals like raccoons, skunks, bats, coyotes, and foxes. So
Speaker 1: at any given time, the vast majority of disease carriers
Speaker 1: are not humans or domestic animals, but wild animals um
Speaker 1: And so if you could cut down on the rates
Speaker 1: of an infection among wild animals, that would downstream cut
Speaker 1: down on the rates of infection and exposure among domestic
Speaker 1: animals and humans. So I was reading about a series
Speaker 1: of programs by the U. S Department of Agriculture, Animal
Speaker 1: and Plant Health Inspection Service Wildlife Services. That's a lot
Speaker 1: of words to essentially seed the wilderness with bait containing
Speaker 1: oral rabies vaccine UH and note that this type of
Speaker 1: vaccine is not nearly as expensive as the UH the
Speaker 1: full human p EP course. But to read from the U.
Speaker 1: S d A website on this program, quote oral rabies
Speaker 1: vaccination or o r V bait is distributed to wildlife
Speaker 1: in targeted areas. This edible bait consists of a satchet
Speaker 1: or plastic packet containing the raboral VRG rabies vaccine. To
Speaker 1: make the bait attractive to wildlife, the sachets containing the
Speaker 1: vaccine are sprinkled with fishmeal coating, or encased inside hard
Speaker 1: fish meal polymer blocks about the size of a matchbox.
Speaker 1: Each year, w S I guess it's Wildlife Services and
Speaker 1: cooperators distribute about six point five million bits in selected
Speaker 1: states to create a zone where raccoon rabies can be contained.
Speaker 1: And I think they've been doing programs like this since
Speaker 1: the nineties. They claim that for every dollar spent on
Speaker 1: the wild r V program, and estimate of somewhere between
Speaker 1: four dollars and thirteen dollars are saved in costs associated
Speaker 1: with rabies transmission into into humans and domestic animals down
Speaker 1: the line, So that sounds like a great intervention. Okay.
Speaker 1: One last response to our episodes on thirst. This one
Speaker 1: comes from Kenny. Kenny says, Hi, Rob and Joe. I
Speaker 1: really enjoyed the first two episodes on thirst. I particularly
Speaker 1: like the discussion around the neural and endocrine systems the
Speaker 1: body uses to maintain the osmolarity of our blood. Since
Speaker 1: you only had time to touch on this, I thought
Speaker 1: I would write in about the mechanism by which the
Speaker 1: kidneys helped to regulate blood volume and osmotic concentration. I
Speaker 1: know it's an odd thing to find mind blowing, but
Speaker 1: it's one of those topics I remember most clearly from
Speaker 1: my biomedical science degree in the late nineties. Each kidney
Speaker 1: contains about a million structures called nephrons. The initial elements
Speaker 1: of the nephron filter the blood, then reabsorb everything you
Speaker 1: want to keep, like glucose, amino acids and much of
Speaker 1: the water. The clever part happens when the filtrate enters
Speaker 1: a structure called the loop of Henley and descends into
Speaker 1: the renal medulla deep within the kidney. The function of
Speaker 1: the loop is to create an osmo larity gradient within
Speaker 1: the surrounding interstitial tissue. It does this through the active
Speaker 1: transport of sodium chloride, meaning salt and water. The osmotic
Speaker 1: concentration of blood is about three hundred milla osmals per leader,
Speaker 1: but the interstitial fluid in the medulla is extremely hypertonic,
Speaker 1: so very salty, and can be as high as twelve
Speaker 1: hundred mill osmoles per leader. Once through the ascending arm
Speaker 1: of the loop, the filtrate is again extremely dilute and
Speaker 1: can have an osmotic concentration as low as seventy two
Speaker 1: a hundred when it enters the collecting duct. This duct
Speaker 1: passes straight down through the osmolarity gradient. If you are dehydrated,
Speaker 1: then anti diuretic hormone acts upon the collecting duct to
Speaker 1: make it permeable to water. As the filtrate descends through
Speaker 1: the osmolality gradient, more and more water diffuses through the
Speaker 1: vessel walls by osmosis, pulled through by the higher concentration
Speaker 1: of salts in the surrounding tissue. The more dehydrated you are,
Speaker 1: the more permeable the collecting duct, and the more concentrated
Speaker 1: the resulting urine. So despite the extreme tonicity of our
Speaker 1: most concentrated urine. It is in fact slightly hypotonic compared
Speaker 1: to the interstitial environment it passed through. In fact, the
Speaker 1: collecting duct is permeable to urea, which some of which
Speaker 1: diffuses out of the duck's lower reaches and further increases
Speaker 1: the osmilarity of the surrounding fluid. On the other hand,
Speaker 1: if you've drunk so much water that you squelch when
Speaker 1: you walk, a d H is almost absent, and that's
Speaker 1: anti diuretic hormone. A d H is almost absent, and
Speaker 1: the collecting duct becomes almost impermeable to water, which means
Speaker 1: that the filtrate will pass straight through as extremely dilute,
Speaker 1: almost colorless urine. The nature of the structure means that
Speaker 1: there is a hard limit to how concentrated humans can
Speaker 1: make their urine. We're not as good at retaining water
Speaker 1: as mammo's more adapted to arid conditions. A camel has
Speaker 1: large numbers of long loops of hinley, which allows it
Speaker 1: to maintain a hypertonic environment in its renal medulla with
Speaker 1: a concentration of more than double that of a human.
Speaker 1: This means that the camel can produce exceptionally concentrated urine
Speaker 1: and retain water for longer. I was also fascinated by
Speaker 1: your discussion on the taste of water. I live in Scotland,
Speaker 1: famous for rain mountains and deep locks. The water from
Speaker 1: our taps is so good, but we are rightly appalled
Speaker 1: by the sorry state of the stuff that comes out
Speaker 1: of the taps south of the border, I guess in England.
Speaker 1: My aunt lives in the south of England, where the
Speaker 1: geology is completely different, and I used to dread the
Speaker 1: tap water down there. It didn't exactly taste of farts,
Speaker 1: but it's deeply unpleasant and I never found it refreshing
Speaker 1: at all. The high levels of calcium and magnesium in
Speaker 1: the water, especially around London, where the water is very hard. Indeed,
Speaker 1: I mean the dishwashers and washing machines can end up
Speaker 1: with serious limescale build ups. Anyway, that's more than enough
Speaker 1: for me. Thanks for all you do, Kenny, uh and
Speaker 1: then Kenny also includes a little cartoon mocking the taste
Speaker 1: of English tap water. Well, Kenny, thank you for the message,
Speaker 1: the the interesting anatomical notes, but also yeah, I traveled
Speaker 1: England with my wife Rachel a few years back. And
Speaker 1: it was a great trip. Uh. England is a wonderful
Speaker 1: country with many treasures. But yes, I distinctly remember the
Speaker 1: tap water tasted so wrong. It it was like it
Speaker 1: had been steeped in a barrel full of chalk and
Speaker 1: discarded latex gloves. But no disrespect to England. Uh. You know,
Speaker 1: London is a place of fractal delights. And while we
Speaker 1: were there, we also went down to the Jurassic Coast
Speaker 1: and walked around with the wild ammonite fossils um, which
Speaker 1: is just great and one of my favorite feelings is
Speaker 1: is finding a fossil in its original exposure setting in
Speaker 1: the outdoors before somebody removes it to a collection or
Speaker 1: a museum. Uh. And if you've never done that, the
Speaker 1: Jurassic Coast is great. It's got ammonites and things all
Speaker 1: over there. But I also recommend I've mentioned this on
Speaker 1: the show before, but the the hikes they offer to
Speaker 1: the trilobite beds of the Burgess Shale in the Canadian Rockies.
Speaker 1: That's one of my all time favorite excursions. Just magical. Anyway,
Speaker 1: I think that is going to be it for today's
Speaker 1: episode of Listener Mail, but we will be back to
Speaker 1: talk to you again soon. Hey. If you're new to
Speaker 1: the show, once again, This is the Stuff to Blow
Speaker 1: Your Mind podcast. This is listener Mail, which we do
Speaker 1: every Monday, but we do core science and culture episodes
Speaker 1: on Tuesdays and Thursdays. We do short form episodes on Wednesdays,
Speaker 1: and then on Fridays, Rob and I usually do a
Speaker 1: casual episode that we call Weird House Cinema where we
Speaker 1: just talk about a weird movie, usually a monster movie
Speaker 1: or something from one of the genres. Uh. If you're
Speaker 1: not subscribed, you can find us wherever you get your podcast.
Speaker 1: Just look up the Stuff to Blow your Mind feed
Speaker 1: or go to stuff to Blow your Mind dot com.
Speaker 1: Big thanks as always to our wonderful audio producer Seth
Speaker 1: Nicholas Johnson. If you would like to get in touch
Speaker 1: with us to maybe have your message featured on a
Speaker 1: future listener Mail episode, or to suggest a topic for
Speaker 1: the show for one of our core episodes, or just
Speaker 1: to say hello, you can email us at contact at
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