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Speaker 1: My Welcome to Stuff to Blow Your Mind, the production

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Speaker 1: of My Heart Radio. Hey, welcome to Stuff to Blow

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Speaker 1: Your Mind. My name is Robert Lamb and I'm Joe McCormick,

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Speaker 1: and we're back with part two of our series on thirst.

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Speaker 1: What are you drinking right now? Absolutely nothing? Oh no, wait,

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Speaker 1: I do have I have water here at my desk.

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Speaker 1: I'm always drinking water. I'm a water guy. You know,

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Speaker 1: some people are really into tea. I almost never drink tea.

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Speaker 1: I go coffee water. That that's pretty much it. Uh,

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Speaker 1: during the daytime hours at least. Oh yeah, well, I'm

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Speaker 1: currently drinking tea. I generally go coffee, uh, te tea, water, tea,

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Speaker 1: and then water and then then when the evening comes,

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Speaker 1: you know, maybe I'll have something something else to drink.

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Speaker 1: But uh yeah, right now it is tea, which is

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Speaker 1: essentially water, but with extra things added to it. You know,

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Speaker 1: I some times get confused about what tea means because

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Speaker 1: I think of tea as being a specific kind of plant, like,

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Speaker 1: isn't there a t tree? Again, I don't know much

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Speaker 1: about tea, so I think about it in that way.

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Speaker 1: But then you can make a tea out of like

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Speaker 1: anything basically that you steep in water. Right, people make

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Speaker 1: mushroom teas, people with all kinds of just oh, we

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Speaker 1: have and plant stuff in water, and that's tea. Also yeah,

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Speaker 1: like I mean, there's there's property and that's generally what

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Speaker 1: I'm when I'm drinking. I'm drinking, you know, a dark

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Speaker 1: tea or maybe a green tea. But also sometimes I'll

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Speaker 1: have a tumeric tea, which is uh like like tumeric

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Speaker 1: and ginger and a little coconut oil and a little

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Speaker 1: honey hot water. But it doesn't actually contain tea, so

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Speaker 1: it's not completely accurate to call it such because it's

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Speaker 1: sort of how not all band aids are technically band

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Speaker 1: aids or xerox it's or whatever. Has this been a

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Speaker 1: terrible intro? Maybe we can cut my tea thing? No, No,

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Speaker 1: this is a This is an intro that the people

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Speaker 1: can relate to. People can thoughts on this. It's always

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Speaker 1: good to start off asking what a word means. So

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Speaker 1: I turns out I know nothing about T. I have

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Speaker 1: no little There you go. We need to come back

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Speaker 1: and do an episode or a series of episodes on T.

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Speaker 1: It's a fascinating subject, fascinating history. Okay, well, we're going

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Speaker 1: to jump back into some of the science that we

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Speaker 1: were talking about in the last episode, where I was

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Speaker 1: reviewing an interesting paper that I had read summarizing the

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Speaker 1: the recent state of research on the biology of thirst.

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Speaker 1: That was it was a paper published in Current Biology.

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Speaker 1: We had to break off in the middle of talking

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Speaker 1: about it. But but before we get back into that, Rob,

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Speaker 1: I think you wanted to talk about the taste of water,

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Speaker 1: which I think is in itself a very interesting subject. Yeah,

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Speaker 1: it's it's a strange one because we probably don't think

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Speaker 1: about it enough, but but we often talk about it,

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Speaker 1: especially when we when we travel from one place to another. Um.

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Speaker 1: We if you look back on I think back on

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Speaker 1: water that you've consumed in the past, may have specific

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Speaker 1: memories of different waters. Um Like, I remember when my

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Speaker 1: family lived in the country and we had well water,

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Speaker 1: and it had a it had a distinctive taste, and

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Speaker 1: I don't I can't say that I loved it, But

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Speaker 1: if I were to encounter the exact same flavor profile again,

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Speaker 1: it would probably make me nostalgic, you know, like it's

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Speaker 1: it's it's a definite flavor that is tied to a

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Speaker 1: definite place. And time warning that this is a little crude,

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Speaker 1: but I don't know of how else to explain it.

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Speaker 1: You've ever been somewhere that had farty water, Um, well,

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Speaker 1: it's kind of sulfury water, kind of kind of like

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Speaker 1: water from the That's kind of what this was like. Yeah,

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Speaker 1: it was that had kind of a a fire and

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Speaker 1: brimstone kind of flavor to it. Okay, that's a more

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Speaker 1: elegant way to put it. Well, the denizens of Hell

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Speaker 1: are not insulted. They're flattered that you would you would

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Speaker 1: compare this foul drinking water to flattens. But um, you know,

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Speaker 1: but then sometimes I don't know, there's there's also beech water,

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Speaker 1: you know, Like I I anytime I'm I'm in Florida

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Speaker 1: and I'm having Florida water, like it has its own

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Speaker 1: it tends to have its own bouquet, its own flavor

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Speaker 1: profile that at the time I'm not enjoying. But then

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Speaker 1: after I'm back and drinking tastier water, I'm kind of

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Speaker 1: kind of long for it, you know, because like this

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Speaker 1: is the water of of of the vacation that I

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Speaker 1: am no longer on that sort of thing. I remember

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Speaker 1: when I was in like a middle school. I went

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Speaker 1: to New Mexico and we went somewhere there where the

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Speaker 1: water was very I don't know, the tap water was

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Speaker 1: almost kind of frothy somehow. It was like a kind

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Speaker 1: of kind of white and cloudy, and I remember thinking

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Speaker 1: it had a strange taste. I don't know what to

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Speaker 1: connect that too, if it was supposed to be like

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Speaker 1: that or not. Yeah, So I guess one thing we

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Speaker 1: can definitely establish here is that there there certainly seems

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Speaker 1: to there is an objective difference in in drinking waters

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Speaker 1: from one place to another. Uh, you know, Atlanta water

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Speaker 1: versus Florida water, that sort of thing. But there's also

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Speaker 1: this wide variety in people just interpret the taste of water. Um.

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Speaker 1: You know, I think we we often think of water

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Speaker 1: as being neutral or tasteless. Um. If you're mixing a cocktail,

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Speaker 1: for example, you don't want to shake it too long

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Speaker 1: with the crushed ice because you will what will happen,

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Speaker 1: You will water it down. Water in this case is

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Speaker 1: the antithesis of an interesting flavor profile. Well. But the

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Speaker 1: other half of that is sometimes people screw up making

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Speaker 1: a drink because they don't shake it with ice at

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Speaker 1: all when they're supposed to, and they don't understand that

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Speaker 1: shaking with ice not only cools the drink, but it

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Speaker 1: also adds a certain amount of water to the drink,

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Speaker 1: which is an important ingredient. Yes, absolutely so, you're supposed

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Speaker 1: to shake a cocktail and you don't. You end up

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Speaker 1: with a drink that's usually too strong or too sweet. Yeah,

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Speaker 1: there's a balance to be maintained there, much like the

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Speaker 1: balance of of water in the human body that we

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Speaker 1: discussed in the last episode. Many of you out there

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Speaker 1: have probably met someone who claims to not like the

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Speaker 1: taste of water. Sometimes they'll these individuals will will use

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Speaker 1: flavored water or other beverages instead, and we'll tend to

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Speaker 1: shy away from just drinking straight water. Um. But I

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Speaker 1: don't know if you're like me, you know, perhaps you've

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Speaker 1: noticed times when a glass of ice water is just

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Speaker 1: super satisfying. Um, you know, particularly on a hot day,

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Speaker 1: like a just a super cold water, lots of ice

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Speaker 1: in it. Um, I would I would tend to. I

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Speaker 1: found myself wanting to categorize that as delicious, though at

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Speaker 1: the same time feeling weird for thinking that because it's

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Speaker 1: like it's water, it I can't say it's delicious. It

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Speaker 1: has no flavor, right, that's what we're we believe. Another

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Speaker 1: another one I really like is the first sip of

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Speaker 1: cold water that I have after I have brushed my teeth. Now,

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Speaker 1: after I've brushed my teeth and rinsed and spit, I'm

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Speaker 1: not drinking um water that way, but yeah, like, after

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Speaker 1: I've brushed my teeth, I've walked into another room, I

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Speaker 1: have a sip of water, super cool and refreshing, agreed,

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Speaker 1: much better than the sip of orange juice after you

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Speaker 1: brush your teeth, which is I don't know if you've

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Speaker 1: ever tried that. It's it's fame disgusting. Oh this is

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Speaker 1: this is always the worst. Really getting into the weeds here.

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Speaker 1: But um, that that feeling when you you were you're

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Speaker 1: busy in the morning, you go brush your teeth, You

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Speaker 1: come back and you find your coffee cup and it

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Speaker 1: still has half a cup of coffee in it. Heartbreaking

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Speaker 1: because you know you can't drink it. Now, if you drink,

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Speaker 1: you can drink it, you can you can throw it back,

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Speaker 1: but it's gonna taste awful. I wonder if anybody's ever

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Speaker 1: done a controlled study of how long you have to

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Speaker 1: wait after brushing your teeth before those those horrible flavor

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Speaker 1: interactions fade away. I don't think it's too long, it's

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Speaker 1: I mean, if I had to venture to guess, I'd

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Speaker 1: say it couldn't be more than like twenty minutes. Right. Yeah. Now,

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Speaker 1: of course, a lot of this, some of this is

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Speaker 1: gonna very culture to culture. In some cultures, it's not

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Speaker 1: it's not considered advisable to drink cold water. You want

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Speaker 1: to drink hot water. Uh, So you know, there's it's gonna,

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Speaker 1: it's gonna, it's gonna vary. There's a lot of cultural

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Speaker 1: stuff going on here as well. Oh, I've never heard

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Speaker 1: of that. What's what's an example of of a culture

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Speaker 1: that favors hot water drinking. There's a connection if Maray services,

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Speaker 1: a connection to traditional Chinese medicine here where um uh,

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Speaker 1: the idea is that it's better for your health to

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Speaker 1: drink hot water as opposed to cold water. But I

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Speaker 1: don't remember any of the deeper details of regarding it all. Right, Well,

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Speaker 1: to get us back on track, you had mentioned that

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Speaker 1: maybe maybe it was wrong to say that tap water,

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Speaker 1: you know, cold water coming in on a hot day

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Speaker 1: was delicious because water itself doesn't really have a taste.

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Speaker 1: And I think this is a common understanding, but is

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Speaker 1: that true? Like it does it have a taste? Does

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Speaker 1: it not have a taste? Does it have a taste.

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Speaker 1: We're just so used to that we can't taste it anymore. Yeah,

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Speaker 1: we'll like to We'll go back to Aristotle. Aristotle was

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Speaker 1: certainly kind of in the no taste camp, stating that

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Speaker 1: it was for the most part tasteless. Uh. The idea

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Speaker 1: that water is it made liver flavors, but it it's

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Speaker 1: in and of itself, does not have flavor. But a

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Speaker 1: lot of a lot of work has gone into this

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Speaker 1: this question of Uh, some some interesting studies. UM. I

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Speaker 1: was reading an article by Berlin Game at All titled

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Speaker 1: Understanding the Basics of Tap Water Taste, publishing the American

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Speaker 1: Water Works Association Journal in two thousand seven. UM, and Uh.

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Speaker 1: They point out that the basically you get the water

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Speaker 1: is going to contain negatively and positively charged ions as minerals.

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Speaker 1: You're gonna find that in your tap water, and that

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Speaker 1: can positively and negatively affect taste. This is especially key,

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Speaker 1: they point out as far as water regulations and reverse

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Speaker 1: os moses go, which is to say, without without getting

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Speaker 1: into all the chemistry, there are certainly differences in water

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Speaker 1: flavor due to different minerals and other elements in the water. Now,

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Speaker 1: another interesting thing about about tap water, especially uh, generally

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Speaker 1: when you're drinking tap water, UH, the drinking water probably

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Speaker 1: contains calcium, magnesium, sodium um. And according to Azila at

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Speaker 1: all In in an article in the Journal of General

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Speaker 1: Internal Medicine from two thousand one titled Comparison of Mineral

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Speaker 1: content of tap water and bottled waters, the mineral content

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Speaker 1: of drinking water UH like this ultimately maybe an important

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Speaker 1: source of daily recommended mineral dosages. UH, certainly in the

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Speaker 1: United States, which was the the area they were looking

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Speaker 1: at here um and UH. And so basically, why we

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Speaker 1: might think of water as being this thing that we

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Speaker 1: would will, let's just purify the heck out of it. Uh,

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Speaker 1: just give me the purest water possible. The purest water

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Speaker 1: possible isn't necessarily going to be the healthiest or the

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Speaker 1: tastiest UM, which I thought that was an interesting distinction.

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Speaker 1: Like when when we when we purchased bottled water, we're

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Speaker 1: not going and by and buying the distilled water usually,

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Speaker 1: I mean, maybe maybe that's what you're doing. But for

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Speaker 1: the most part, people are are are not buying distilled

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Speaker 1: water for drinking purposes, right. But distilled water, even though

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Speaker 1: it is probably the purest form of water you can get,

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Speaker 1: is not necessarily better for any reason, not for not

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Speaker 1: for health or for experience of drinking. Now, in terms

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Speaker 1: of just trying to get down to the question, though, well,

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Speaker 1: what what does it taste like? Okay, you know we're

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Speaker 1: saying it can can go a little in this direction,

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Speaker 1: a little in that direction. We have these mineral components, uh,

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Speaker 1: you know, adding to the the flavor. But but what

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Speaker 1: is the taste itself? And I think one of the

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Speaker 1: interesting things about that question is that it forces you

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Speaker 1: to take a step back and think about taste itself. Um.

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Speaker 1: You know, taste involves both sensations on the tongue and

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Speaker 1: olfactory information as well. So it's not only it's not

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Speaker 1: only tasting with the mouth, it's smelling, uh whatever you

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Speaker 1: know it is that you're consuming as well. Um and uh.

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Speaker 1: And certainly we do taste contents in the water, though

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Speaker 1: under ideal circumstances that not that's not going to push

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Speaker 1: you hard in any direction. But but obviously if you

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Speaker 1: dilute some sugar and a glass of the universal solvent

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Speaker 1: and drink it, you'll find it sweet saltwater taste salty.

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Speaker 1: Your sense of taste is still weighing in on the water.

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Speaker 1: But in terms of the this kind of brings us

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Speaker 1: back to the same question. Does the water itself have

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Speaker 1: a taste or is it just the vehicle for these

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Speaker 1: various flavors, be it salt or sugar, or you know,

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Speaker 1: a slight hint of of magnesium, that sort of thing.

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Speaker 1: So one idea proposed in the sixties and seventies by

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Speaker 1: psychologist Linda barda Shut was that the taste of water

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Speaker 1: is more of an after taste of prior eating and drinking.

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Speaker 1: And this too, I guess it is more in line

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Speaker 1: with the idea of water as the vehicle flavor, but

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Speaker 1: something that is in and of itself flavorless. So the

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Speaker 1: idea would be that, like when you take a drink

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Speaker 1: of water, you are somehow re experiencing flavors of foods

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Speaker 1: you may have eaten most recently. Yeah, and this this

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Speaker 1: will become important. And again we have to realize that

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Speaker 1: when you take a sip of water, you were not

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Speaker 1: introducing water no matter how sterile your water is, your

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Speaker 1: mouth is is not sterile. You know your your mouth

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Speaker 1: is going to even if you if you've just brush

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Speaker 1: your teeth, great, but that you're going to have some

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Speaker 1: semblance of of the of that experience in your mouth.

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Speaker 1: If you're eating dinner, you know there's going to be

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Speaker 1: the hint of food or drink as well. So, yeah,

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Speaker 1: you're not introducing the water into a neutral place. If

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Speaker 1: nothing else you your saliva is present. Emily Underwood wrote

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Speaker 1: in an excellent short seventeen piece for the American Association

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Speaker 1: for the Advancement of Science on this topic, the Flavor

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Speaker 1: of Water, um and uh. At one point she's a

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Speaker 1: citing Zachary Knight, oh, who is one of the three

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Speaker 1: authors of the research summary thirst in Current Biology that

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Speaker 1: I was referring to in the last episode, and I'll

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Speaker 1: be talking about again in a few minutes. Yeah, So

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Speaker 1: Underwood points to um, something that that we discussed in

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Speaker 1: the last episode that you know, ultimately, when we're getting

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Speaker 1: into taste, when we're getting into water detection in the mouth,

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Speaker 1: the molecular and cellular mechanisms here are are not that

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Speaker 1: well understood. And then she also touches on some of

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Speaker 1: nights UM research regarding the thirst trigger, Uh, you know

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Speaker 1: where where that is seems to locate in the brain

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Speaker 1: and then ultimately what's where is the trigger in the

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Speaker 1: in the rest of the body. But we'll come back

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Speaker 1: to that in a bit. Yeah, but I guess there

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Speaker 1: are somewhat separate questions for can you detect water in

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Speaker 1: your mouth versus can you taste water? I mean those

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Speaker 1: are slightly slightly different, right, yeah, well, but but then again,

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Speaker 1: when you start thinking about like what what taste is,

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Speaker 1: maybe they're not that different, like it's but but it

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Speaker 1: basically comes down to, yeah, it's not about interpreting these

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Speaker 1: minerals or sweetness or saltiness, but like the just the

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Speaker 1: basic signal of it is water. It is in my mouth,

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Speaker 1: you know, um, And then ultimately being able to tell

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Speaker 1: if something is not water, um, like or if it

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Speaker 1: or if the water is you know, too far in

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Speaker 1: a particular direction, like oh it is it is actually

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Speaker 1: oil and water and not just water, Um, I wanted water.

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Speaker 1: That's sort of question. So researchers have been trying to

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Speaker 1: isolate water sensing taste receptor. It sells on the tongue

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Speaker 1: um of a particular note here is the paper the

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Speaker 1: segular Mechanism for Water Detection in the Mammalian Taste system

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Speaker 1: by Zocchi at All published in Nature Neuroscience in UM.

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Speaker 1: This was a team I believe from the California Institute

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Speaker 1: of Technology in Pasadena, and they were working with mice

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Speaker 1: UH and this is this is one of those the

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Speaker 1: studies that I mean, it's already an interesting area, like

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Speaker 1: using mice to figure out how we're tasting, but then

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Speaker 1: it goes in ultimately strange directions that are pretty fascinating.

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Speaker 1: So they were they were using different varieties of mice

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Speaker 1: with specific types of taste receptor cells genetically knocked out

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Speaker 1: in order to try and isolate which ones were seemingly

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Speaker 1: useful in tasting water. And they found that the acid

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Speaker 1: sensing sour taste receptor cells seemed to be the most involved.

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Speaker 1: Mice with those knocked out took far longer distinguishing oily

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Speaker 1: water from clean water. UM. In the words of the study,

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Speaker 1: this quote compromise discrimination between water and non aqueous fluids.

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Speaker 1: So these cells seem like they may they may well

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Speaker 1: be very much involved in UH in the process. Interesting, Okay,

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Speaker 1: So if we are actually tasting water, it may rely

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Speaker 1: more on the cells that normally taste sourness or acidity

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Speaker 1: than other taste receptor cells, or at least in mice,

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Speaker 1: and if if the same held true in humans, that

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Speaker 1: would be the case for us. But this is where

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Speaker 1: the mouse experiment from this team gets weird. Um. So

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Speaker 1: to further test this out, they bread mice that could

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Speaker 1: taste light with these acids sensing t rcs UH taste

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Speaker 1: receptor cells. They train them to drink water from a pigot,

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Speaker 1: and they replace that'spigot with an optic fiber cable, so

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Speaker 1: they they they apparently treated the mice in this case,

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Speaker 1: they apparently treated the light as if they were tasting water,

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Speaker 1: but they didn't stop. They kept drinking the light long

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Speaker 1: after UH they would have normally stopped drinking water. So

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Speaker 1: the acid sensing t rcs might be involved in triggering drinking,

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Speaker 1: but they might not be involved in stopping you from drinking,

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Speaker 1: like saying, okay, well that's that's all the water I

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Speaker 1: need to drink right now, um and um. And I'm

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Speaker 1: not sure there may be other complications there. I mean,

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Speaker 1: once you you have an animal drinking light and not

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Speaker 1: actual water. Um, it just seems to me like there

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Speaker 1: might there might be other things going on there on

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Speaker 1: in a very physical basis. So this would be taste

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Speaker 1: receptor cells in the mouth, but they're like optically sensitive cells.

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Speaker 1: Am I right about this? It's literally like drinking light

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Speaker 1: with their mouth, like letting light shine into the oral cavity.

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Speaker 1: Yes it uh, I mean it sounds insane and you

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Speaker 1: say it out loud, but but yeah, there's there's actually

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Speaker 1: a YouTube video about it from Science Magazine titled these

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Speaker 1: mice are drinking light. H So if anyone needs to

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Speaker 1: actually see what we're talking about here, pull that up.

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Speaker 1: And yeah, it just it's it's a this, this black

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Speaker 1: mouse going up to this, um, this little receptacle, and

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Speaker 1: it appears to be drinking, but there's blue light flooding

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Speaker 1: out of the hole, okay, and it's got light sensitive

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Speaker 1: cells in its mouth. So the mouse's brain is reacting

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Speaker 1: as if by shining light into its mouth it was

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Speaker 1: swallowing water. Yes, that's crazy, man, Yeah it is. This

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Speaker 1: is this is it's it's it's mind blowing on several

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Speaker 1: levels here. Um. So ultimately this this all might be

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Speaker 1: related to changes in pH level. When in a normal situation,

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Speaker 1: when you know, a mouse or any mammal supposedly is

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Speaker 1: drinking something that is not light. When it it tries

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Speaker 1: out the water, saliva is washing around in the mouth,

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Speaker 1: and the removal of saliva might be key to sensing water. Again,

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Speaker 1: coming back to what we said earlier about uh, you know,

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Speaker 1: water is not entering into a neutral environment when it

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Speaker 1: goes in your mouth. It's going to interact with at

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Speaker 1: least saliva, and in doing so that might change the

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Speaker 1: pH level which triggers these um these t r c

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Speaker 1: s on the tongue. Um. That seems to be the

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Speaker 1: basic framework we're potentially looking at here. Oh that's interesting.

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Speaker 1: So at least according to the idea here, part of

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Speaker 1: the sensation of of drinking water might be the water's

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Speaker 1: ability to wash natural saliva out of the mouth. Right, So,

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Speaker 1: of course standard caveat that more researches is required, And

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Speaker 1: then we still don't we still don't have this one, Kno,

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Speaker 1: But it's yeah, it's it. Ultimately, it makes you rethink

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Speaker 1: again what taste actually is and consider there there may

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Speaker 1: be precise triggers in place for detecting water and distinguish

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Speaker 1: it from other liquids, and then also letting you know

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Speaker 1: that you have had enough water. Like all these things

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Speaker 1: that we just take for granted, we think of them

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Speaker 1: as we think of them as choices that we make,

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Speaker 1: like I have to, I have, I am, I've decided

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Speaker 1: now I must have water. I have decided now that

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Speaker 1: I don't need any more water. But but these are

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Speaker 1: all tied into the you know, this intricate biological system.

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Speaker 1: Thank thank Alright, well, Rob, if you're ready, I wanted

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Speaker 1: to discuss some more of the things I was reading

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Speaker 1: in that article and Current Biology that was about the

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Speaker 1: biology of thirst. Again. This was by David Leeb, Christopher Zimmerman,

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Speaker 1: and Zachary Knight. Let's do it all right now. We

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Speaker 1: already talked about some of the conditions that will trigger

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Speaker 1: thirst and water seeking behavior in animals such as rodents

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Speaker 1: and humans. Uh uh. Commonly, one thing would be a

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Speaker 1: decrease in water volume in the body, but another thing

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Speaker 1: would be an increase in what's called blood OSMO reality

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Speaker 1: O S M O L A L I T Y.

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Speaker 1: I spell it because that word will keep coming up

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Speaker 1: in this discussion. OSM reality is the concentration of substances

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Speaker 1: dissolved in the water content of the body, so the

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Speaker 1: blood osmolality will go up. Say, if you consume salt

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Speaker 1: or consume other kinds of salts of various minerals, whether

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Speaker 1: that's sodium or magnesium or whatever, there are lots of

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Speaker 1: things dissolved in the blood, and is the concentration of

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Speaker 1: those things dissolved in the blood goes up. That's that's

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Speaker 1: known as increasing OSMO reality. And as we discussed in

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Speaker 1: the last episode, your your awsom reality really needs to

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Speaker 1: be pretty tightly constrained within an ideal range, or it

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Speaker 1: can start leading to system wide problems with cellular function

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Speaker 1: because cells need a pretty tightly controlled electrochemical gradient on

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Speaker 1: each side of their their membranes in order to control

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Speaker 1: the passage of ions in and out of the cell

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Speaker 1: to you know, take in things, the cell needs to

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Speaker 1: release waste products and so forth. So uh So, in

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Speaker 1: order for your body to work right, it needs to

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Speaker 1: have the right level of the right concentration of things

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Speaker 1: like salts dissolved in its water. But you also have

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Speaker 1: to keep your your body, your your body's water volume

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Speaker 1: at the right level, uh in order to maintain ideal

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Speaker 1: blood pressure. Because that blood's gotta flow, and if if

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Speaker 1: you suddenly are to remove a lot of liquid from

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Speaker 1: the body, suddenly the heart has to pump harder and

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Speaker 1: harder to get the red blood cells to do all

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Speaker 1: the different parts of your body. So keeping up keeping

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Speaker 1: up the right amount of water in the body and

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Speaker 1: the correct concentration of substances dissolved in that water is crucial.

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Speaker 1: And that dichotomy we talked about last time actually breaks

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Speaker 1: down into two distinct types of dehydration that the authors

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Speaker 1: talk about. And these two types of dehydration actually lead

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Speaker 1: to different behavioral reactions in animals. So you can have

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Speaker 1: dehydration within cells or dehydration between cells. A loss of

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Speaker 1: water from within cells, known as intracellular dehydration, is usually

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Speaker 1: caused by high blood osmolality, so the introduction of salts

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Speaker 1: or other things like that into the body. This draws

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Speaker 1: water out of cells by osmosis and causes the cells

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Speaker 1: to shrink, which certainly doesn't sound good. Standard behavioral response

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Speaker 1: to to uh that kind of thing. That intracellular dehydration

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Speaker 1: is thirst. You want water, so you go get it.

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Speaker 1: Loss of water from between cells is known as extracellular dehydration,

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Speaker 1: and this usually is caused by a loss of total

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Speaker 1: blood volume, for example by bleeding. You know, if you

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Speaker 1: cut yourself and lose a bunch of liquid out of

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Speaker 1: your arm or something, you will lose total blood content

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Speaker 1: without changing the body's osmolality. You know, you think about

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Speaker 1: it that way, like you're the liquid is going down,

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Speaker 1: but you're not changing how salty the liquid that's left is.

429
00:24:02,880 --> 00:24:05,960
Speaker 1: So in order to recover from that condition, you will

430
00:24:06,000 --> 00:24:10,040
Speaker 1: actually need both water and salt to replenish the lost volume.

431
00:24:10,560 --> 00:24:14,359
Speaker 1: Just drinking water alone would leave your osmolality too low.

432
00:24:14,920 --> 00:24:18,400
Speaker 1: So the behavioral response to a loss of total water

433
00:24:18,600 --> 00:24:23,080
Speaker 1: content or content from between cells is usually thirst plus

434
00:24:23,240 --> 00:24:25,840
Speaker 1: what the author is called salt appetite. You want water

435
00:24:26,000 --> 00:24:30,160
Speaker 1: and salt at the same time. But interestingly, many things

436
00:24:30,280 --> 00:24:34,000
Speaker 1: that happened to the body cause both types of dehydration

437
00:24:34,040 --> 00:24:36,840
Speaker 1: at the same time. Uh. Then the example they give

438
00:24:36,880 --> 00:24:39,159
Speaker 1: is sweating. This is very common, right, you know. You

439
00:24:39,600 --> 00:24:41,920
Speaker 1: you go out in the sun and you sweat. Well,

440
00:24:42,080 --> 00:24:45,600
Speaker 1: sweat is not only a loss of blood volume. Uh,

441
00:24:45,800 --> 00:24:49,840
Speaker 1: sweat is salty, but sweat is actually less salty than

442
00:24:49,920 --> 00:24:53,240
Speaker 1: your blood. So if your body is losing liquid that

443
00:24:53,440 --> 00:24:57,040
Speaker 1: is less salty than its water content overall, like sweat

444
00:24:57,240 --> 00:25:00,280
Speaker 1: is the salt content of what's left behind and is

445
00:25:00,359 --> 00:25:04,520
Speaker 1: therefore increasing. Does that make sense, So the extra salt

446
00:25:04,640 --> 00:25:07,920
Speaker 1: left over inside you when you sweat causes an increase

447
00:25:07,960 --> 00:25:11,679
Speaker 1: in blood osmlality, again triggering a thirst for water. It's

448
00:25:11,760 --> 00:25:14,920
Speaker 1: kind of counterintuitive because if you ever do taste sweat it,

449
00:25:15,080 --> 00:25:16,920
Speaker 1: you know it tastes salty, so you would think it

450
00:25:16,960 --> 00:25:19,439
Speaker 1: would feel like you're losing salt, but you're actually gaining

451
00:25:19,480 --> 00:25:22,320
Speaker 1: salt is in relationship to the amount of water left

452
00:25:22,359 --> 00:25:24,560
Speaker 1: in you. Yeah, I think we've touched that on this

453
00:25:24,680 --> 00:25:27,520
Speaker 1: on the show before that that sometimes we give too

454
00:25:27,600 --> 00:25:30,680
Speaker 1: much credit to sweat in its ability to remove things

455
00:25:30,760 --> 00:25:35,480
Speaker 1: from our body, certainly when some arguments for the removal

456
00:25:35,560 --> 00:25:39,199
Speaker 1: of impurities through sweat, for example, Oh yeah, yeah, right

457
00:25:39,280 --> 00:25:41,239
Speaker 1: with people who think that you can like cleanse all

458
00:25:41,280 --> 00:25:44,320
Speaker 1: the toxins by sweating or something, I mean, sweating is great. No,

459
00:25:44,520 --> 00:25:46,960
Speaker 1: no knocking on sweat and uh and if memory serves

460
00:25:46,960 --> 00:25:48,920
Speaker 1: like I mean, there is some toxin removal, but not

461
00:25:49,560 --> 00:25:52,640
Speaker 1: not anywhere near as good as say, good old fashioned urination.

462
00:25:52,720 --> 00:25:55,680
Speaker 1: I mean, that's that's right, when we have urination exactly.

463
00:25:56,200 --> 00:25:58,200
Speaker 1: So I guess from here we go on to talk

464
00:25:58,240 --> 00:26:03,680
Speaker 1: about how the brain senses and monitors osmolality. Uh. This

465
00:26:03,880 --> 00:26:06,760
Speaker 1: is what the authors say is quote, probably the most

466
00:26:06,920 --> 00:26:10,560
Speaker 1: important homeostatic signal for drinking in everyday life is the

467
00:26:10,640 --> 00:26:13,920
Speaker 1: brain's ability to monitor osmolality. That's what's going to be

468
00:26:14,200 --> 00:26:17,840
Speaker 1: causing you to go drink water. Um. And the authors

469
00:26:17,880 --> 00:26:20,560
Speaker 1: point out some interesting things, one of which is that

470
00:26:20,720 --> 00:26:25,240
Speaker 1: when blood osmolality and blood volume are both threatened at

471
00:26:25,280 --> 00:26:29,040
Speaker 1: the same time, for example, if they both increase above

472
00:26:29,119 --> 00:26:32,400
Speaker 1: the ideal range at the same time, the body places

473
00:26:32,440 --> 00:26:37,399
Speaker 1: a higher priority on defending the the ideal osmolality than

474
00:26:37,480 --> 00:26:41,240
Speaker 1: it does on defending volume. So examples of this would be,

475
00:26:41,359 --> 00:26:45,720
Speaker 1: you know, hypernatremia having too much sodium, or hyperglycemia having

476
00:26:45,800 --> 00:26:49,040
Speaker 1: too much glucose in the blood. Whatever it is. The

477
00:26:49,720 --> 00:26:52,400
Speaker 1: state of having too high of an osm reality, which

478
00:26:52,440 --> 00:26:56,680
Speaker 1: they call hyper tonicity, is probably more threatening, more of

479
00:26:56,760 --> 00:27:00,399
Speaker 1: a danger overall than than having not quite the right

480
00:27:00,440 --> 00:27:04,239
Speaker 1: amount of water volume in your body. But anyway, well,

481
00:27:04,320 --> 00:27:06,520
Speaker 1: you know, so what takes care of this whole job, Well,

482
00:27:06,560 --> 00:27:09,680
Speaker 1: you've got some physical structures in your brain that sort

483
00:27:09,720 --> 00:27:12,760
Speaker 1: of that dip their finger into the soup to to

484
00:27:13,000 --> 00:27:15,600
Speaker 1: to taste it for salt and uh and and let

485
00:27:15,680 --> 00:27:18,399
Speaker 1: you know what's going on. Both of them are small,

486
00:27:18,600 --> 00:27:21,640
Speaker 1: they reside in the fore brain, and they are known

487
00:27:21,840 --> 00:27:25,040
Speaker 1: as first of all, the sub formical organ or SFO,

488
00:27:25,880 --> 00:27:29,879
Speaker 1: and then the organum vasculosum of the lamina terminalis or

489
00:27:29,960 --> 00:27:34,480
Speaker 1: ov LT. Now you've probably heard before of something called

490
00:27:34,600 --> 00:27:38,679
Speaker 1: the blood brain barrier. This is a system of border

491
00:27:38,840 --> 00:27:42,440
Speaker 1: cells that prevent things that happen to be floating around

492
00:27:42,520 --> 00:27:46,440
Speaker 1: in the blood from passing non selectively into the brain.

493
00:27:47,280 --> 00:27:49,440
Speaker 1: So you know, the brain does need blood. It has

494
00:27:49,480 --> 00:27:53,159
Speaker 1: to receive oxygen and other nutrients from blood flow, but

495
00:27:53,400 --> 00:27:57,679
Speaker 1: the brain has to also protect itself against totally unregulated

496
00:27:57,800 --> 00:28:00,919
Speaker 1: exchange with the blood. And there may be multiple reasons

497
00:28:01,000 --> 00:28:03,800
Speaker 1: for this, but one of the main ones I've seen

498
00:28:04,320 --> 00:28:08,760
Speaker 1: is that this prevents blood borne pathogens from infecting brain tissue,

499
00:28:08,800 --> 00:28:12,680
Speaker 1: so that seems important. So in regions where it's active,

500
00:28:12,720 --> 00:28:16,399
Speaker 1: the blood brain barrier only allows selective passage of certain

501
00:28:16,440 --> 00:28:19,600
Speaker 1: types of material from the blood into the neurons. But

502
00:28:20,000 --> 00:28:22,480
Speaker 1: if you're part of the brain that needs to get

503
00:28:22,680 --> 00:28:26,000
Speaker 1: raw data about the contents of the blood moment by moment,

504
00:28:26,520 --> 00:28:29,600
Speaker 1: apparently it won't do to be hiding behind this protective

505
00:28:29,640 --> 00:28:32,800
Speaker 1: fence of cells. So, according to the authors here, the

506
00:28:33,000 --> 00:28:35,439
Speaker 1: SFO and the o v l T, though they are

507
00:28:35,560 --> 00:28:39,240
Speaker 1: in the brain, are located outside the blood brain barrier,

508
00:28:39,440 --> 00:28:42,720
Speaker 1: so they can sort of taste the blood river unfiltered,

509
00:28:42,920 --> 00:28:45,400
Speaker 1: undiluted to get a raw sense of what's going on.

510
00:28:46,320 --> 00:28:49,080
Speaker 1: To read directly from the paper here quote, it is

511
00:28:49,200 --> 00:28:52,800
Speaker 1: thought that these SFO and ov LT neurons monitor the

512
00:28:52,880 --> 00:28:59,160
Speaker 1: blood osmolality directly, possibly via stretch sensitive ion channels embedded

513
00:28:59,240 --> 00:29:03,360
Speaker 1: in their plasma membranes that detect changes in cell volume

514
00:29:03,480 --> 00:29:08,640
Speaker 1: following intracellular dehydration. However, the identity of the specific ion

515
00:29:08,800 --> 00:29:12,640
Speaker 1: channel or other protein responsible for OSMO sensing by these

516
00:29:12,720 --> 00:29:16,920
Speaker 1: neurons is unknown. Furthermore, the possibility cannot be excluded that

517
00:29:17,040 --> 00:29:20,480
Speaker 1: other cell types such as galia play an important role

518
00:29:20,560 --> 00:29:24,960
Speaker 1: in OSMO sensation. So here they they identify, they put

519
00:29:25,000 --> 00:29:27,080
Speaker 1: the flag up for One more thing that hasn't fully

520
00:29:27,240 --> 00:29:29,880
Speaker 1: been figured out in in the science of thirst is

521
00:29:30,280 --> 00:29:34,080
Speaker 1: what is the direct molecular mechanism that the neurons in

522
00:29:34,160 --> 00:29:38,640
Speaker 1: these brain regions use to detect changes in blood osmolality.

523
00:29:38,800 --> 00:29:42,000
Speaker 1: It maybe these stretched sensitive cells that you know, get

524
00:29:42,120 --> 00:29:45,560
Speaker 1: dehydrated and then send information based on that to to

525
00:29:45,760 --> 00:29:48,640
Speaker 1: the brain regions that then filter out to to other

526
00:29:48,680 --> 00:29:51,440
Speaker 1: brain regions from there. But we don't know for sure

527
00:29:51,960 --> 00:29:57,720
Speaker 1: anyway that is sensing intracellular dehydration or increases in blood osmolality.

528
00:29:57,840 --> 00:30:00,880
Speaker 1: But what about that other kind extra cell or dehydration

529
00:30:01,200 --> 00:30:06,120
Speaker 1: where the blood volume actually decreases overall, such as after bleeding. Well,

530
00:30:06,360 --> 00:30:10,440
Speaker 1: decreases in blood volume are known as hypovolemia, like low

531
00:30:10,600 --> 00:30:14,600
Speaker 1: volume hypovolemia UH, and they correspond with a decrease in

532
00:30:14,800 --> 00:30:20,360
Speaker 1: blood pressure hypotension UH and the body's reactions to hypotension

533
00:30:21,040 --> 00:30:25,080
Speaker 1: take places sort of a complex chain of mechanisms involving

534
00:30:25,200 --> 00:30:29,840
Speaker 1: multiple multiple organs and several forms of a hormone, very

535
00:30:29,880 --> 00:30:35,760
Speaker 1: important hormone called angiotenson. You might see this abbreviated sometimes

536
00:30:36,160 --> 00:30:39,120
Speaker 1: with like capital letters A in G I and then

537
00:30:39,160 --> 00:30:42,200
Speaker 1: maybe A in G I I for Angiotenson one and

538
00:30:42,320 --> 00:30:46,240
Speaker 1: angiotensin two. Apparently the most crucial form of the hormone

539
00:30:46,320 --> 00:30:50,280
Speaker 1: is Angiotenson two, which causes things like the narrowing of

540
00:30:50,360 --> 00:30:53,400
Speaker 1: blood vessels. So if you shrink blood vessels and make

541
00:30:53,440 --> 00:30:56,720
Speaker 1: them smaller, that helps keep blood pressure up when volume

542
00:30:56,840 --> 00:31:00,880
Speaker 1: is low uh, and it also leads to water reuptake

543
00:31:01,000 --> 00:31:03,840
Speaker 1: by the kidneys. The kidneys are like holding fast to

544
00:31:03,920 --> 00:31:06,840
Speaker 1: the water content rather than just squandering it as they

545
00:31:06,920 --> 00:31:09,080
Speaker 1: might if you had plenty of water in your body.

546
00:31:09,640 --> 00:31:12,720
Speaker 1: And there's evidence that the presence of angiotenson to this

547
00:31:12,840 --> 00:31:16,560
Speaker 1: hormone also causes a thirst drive to be generated in

548
00:31:16,640 --> 00:31:22,400
Speaker 1: the brain, primarily involving the SFO or the sub formical organ. Interestingly,

549
00:31:22,720 --> 00:31:26,360
Speaker 1: in rodents, if you just give them straight Angiotenson two,

550
00:31:26,920 --> 00:31:31,120
Speaker 1: it causes what the authors call profound water consumption, just

551
00:31:31,320 --> 00:31:35,840
Speaker 1: like you know, voluminous drinking of water. But in humans,

552
00:31:35,920 --> 00:31:40,000
Speaker 1: apparently Angiotenson two levels quote do not correlate well with

553
00:31:40,120 --> 00:31:44,200
Speaker 1: the perception of thirst, and infusions of physiological levels of

554
00:31:44,320 --> 00:31:49,800
Speaker 1: Angiotenson to do not stimulate drinking. Interesting, so, perhaps while

555
00:31:50,040 --> 00:31:53,920
Speaker 1: this hormone does things to increase blood pressure, like constrict

556
00:31:53,960 --> 00:31:57,160
Speaker 1: blood vessels and cause water reuptake by the kidneys, it

557
00:31:57,280 --> 00:32:00,160
Speaker 1: does not make us thirsty for water like it us

558
00:32:00,200 --> 00:32:04,560
Speaker 1: and other animals for some reason the author's right quote Well,

559
00:32:04,600 --> 00:32:07,760
Speaker 1: this suggests that Angiotenson too might be less important for

560
00:32:07,840 --> 00:32:11,760
Speaker 1: regulation of drinking and humans. Interpretation of these negative results

561
00:32:11,840 --> 00:32:15,920
Speaker 1: is complicated by the fact that peripheral infusion of angiotenson

562
00:32:15,960 --> 00:32:19,880
Speaker 1: too rapidly increases blood pressure, which can then feed back

563
00:32:20,000 --> 00:32:23,880
Speaker 1: to counteract any effects of angiotenson too on thirst. So

564
00:32:24,000 --> 00:32:27,840
Speaker 1: maybe they're just complicated balancing interactions here that when you know,

565
00:32:27,920 --> 00:32:32,680
Speaker 1: if you directly infuse this hormone, it increases blood pressure,

566
00:32:32,760 --> 00:32:36,320
Speaker 1: which has other downstream effects which which counteract the onset

567
00:32:36,400 --> 00:32:39,880
Speaker 1: of thirst. Okay, I mean, I guess just it just

568
00:32:39,960 --> 00:32:42,400
Speaker 1: goes to show, you know, one of the factors of

569
00:32:43,120 --> 00:32:46,480
Speaker 1: experiments with with with mice and other non human mammals

570
00:32:46,600 --> 00:32:48,760
Speaker 1: is that we have a whole lot in common with them,

571
00:32:48,800 --> 00:32:52,000
Speaker 1: but not everything is going to um is going to

572
00:32:52,040 --> 00:32:54,280
Speaker 1: apply to us one to one, Right, A lot does,

573
00:32:54,360 --> 00:33:03,600
Speaker 1: but not everything. Okay, But anyway, I guess what we're

574
00:33:03,640 --> 00:33:06,520
Speaker 1: trying to uh figure out here is building a bridge

575
00:33:06,600 --> 00:33:09,960
Speaker 1: from our existing knowledge about these brain regions that play

576
00:33:09,960 --> 00:33:13,800
Speaker 1: a role in monitoring the body's osmolality and water content

577
00:33:14,480 --> 00:33:17,600
Speaker 1: and UH and regular in these hormones that helped regulate

578
00:33:17,640 --> 00:33:22,080
Speaker 1: the body's physiologic response to dehydration, and how that connects

579
00:33:22,160 --> 00:33:25,400
Speaker 1: to the actual behavior and the drives that we since

580
00:33:25,440 --> 00:33:29,200
Speaker 1: when we get thirsty and go get water. Um. So

581
00:33:29,560 --> 00:33:32,960
Speaker 1: there there are sort of system wide homeostatic responses when

582
00:33:33,160 --> 00:33:35,720
Speaker 1: when we get dehydrated again, the s f O and

583
00:33:35,800 --> 00:33:38,720
Speaker 1: the O v l T together with another region in

584
00:33:38,840 --> 00:33:41,960
Speaker 1: between them, the media and pre optic nucleus or m

585
00:33:42,040 --> 00:33:45,320
Speaker 1: n p O. These three regions together comprise a hub

586
00:33:45,480 --> 00:33:48,280
Speaker 1: called the lamina terminalys. This is sort of the brain's

587
00:33:48,360 --> 00:33:52,640
Speaker 1: fluid control center. What is fairly well understood is the

588
00:33:52,800 --> 00:33:56,360
Speaker 1: the autonomic and neuroendocrine pathways by which the body responds

589
00:33:56,400 --> 00:33:59,120
Speaker 1: to dehydration. You know, all these things we've been talking about,

590
00:33:59,600 --> 00:34:02,760
Speaker 1: the the angiotenson to the constriction of blood vessels to

591
00:34:02,840 --> 00:34:06,320
Speaker 1: increase blood pressure, water reuptake by the kidneys, the release

592
00:34:06,360 --> 00:34:08,840
Speaker 1: of other hormones, and not just angiotenson, but things like

593
00:34:08,960 --> 00:34:13,000
Speaker 1: vasa pressin and oxytocin. But what is less well understood

594
00:34:13,120 --> 00:34:16,440
Speaker 1: are the mechanisms leading to the generation of thirst as

595
00:34:16,480 --> 00:34:19,799
Speaker 1: a motivation state. But we know some things that are

596
00:34:19,960 --> 00:34:22,680
Speaker 1: very interesting. So to come back to something you actually

597
00:34:22,760 --> 00:34:27,320
Speaker 1: mentioned earlier in the episode, Rob, the brains regulation of

598
00:34:27,440 --> 00:34:32,040
Speaker 1: water drinking is not based only on the current osmolality

599
00:34:32,160 --> 00:34:34,400
Speaker 1: of the blood. So it's not just these brain regions

600
00:34:34,520 --> 00:34:37,280
Speaker 1: that you know. Dip a finger in and see how salty.

601
00:34:37,320 --> 00:34:40,799
Speaker 1: The soup is the brain also appears to change our

602
00:34:40,920 --> 00:34:45,920
Speaker 1: motivation to drink water before changes actually show up in

603
00:34:46,040 --> 00:34:51,520
Speaker 1: the blood. Their behavior changes that occur in anticipation of

604
00:34:51,719 --> 00:34:55,959
Speaker 1: changes in osmolality. So what would this mean in plain English? Okay,

605
00:34:56,000 --> 00:34:58,600
Speaker 1: so you're out in the hot sun wrestling alligators, or

606
00:34:58,680 --> 00:35:00,239
Speaker 1: you know, you're working up a sweat, whate it is

607
00:35:00,320 --> 00:35:03,320
Speaker 1: you're doing, and you come in, you get in the shade,

608
00:35:03,480 --> 00:35:06,560
Speaker 1: and you drink a nice glass of water. When you

609
00:35:06,800 --> 00:35:10,279
Speaker 1: do that, there is actually a delay on the order

610
00:35:10,400 --> 00:35:13,480
Speaker 1: of tens of minutes. It might be ten, twenty or

611
00:35:13,560 --> 00:35:17,120
Speaker 1: even more minutes before the water that you just drank

612
00:35:17,680 --> 00:35:21,280
Speaker 1: is fully absorbed by the digestive system and added into

613
00:35:21,520 --> 00:35:24,359
Speaker 1: the blood. However, it might just take you a few

614
00:35:24,520 --> 00:35:27,880
Speaker 1: seconds to drink a glass of water and then decide

615
00:35:27,920 --> 00:35:31,799
Speaker 1: whether you're going to drink more. So, if it's taking

616
00:35:31,840 --> 00:35:35,520
Speaker 1: your body tens of minutes to fully incorporate the water

617
00:35:35,680 --> 00:35:38,200
Speaker 1: you've just consumed and for that to you know, show

618
00:35:38,280 --> 00:35:41,120
Speaker 1: up in a blood as molality test, how come you

619
00:35:41,200 --> 00:35:45,360
Speaker 1: don't just keep drinking water constantly until that happens. You know,

620
00:35:45,480 --> 00:35:48,799
Speaker 1: you don't, even if you're thirsty, you don't usually drink

621
00:35:48,840 --> 00:35:51,359
Speaker 1: a glass of water and then just fill up another one,

622
00:35:51,600 --> 00:35:54,960
Speaker 1: and another and another and another for you know, fifteen

623
00:35:55,000 --> 00:35:58,080
Speaker 1: minutes or something. If your level of thirst were only

624
00:35:58,200 --> 00:36:00,680
Speaker 1: based on your blood oz molality, you might do that.

625
00:36:00,960 --> 00:36:04,239
Speaker 1: You might kill yourself just drinking gallons of water while

626
00:36:04,280 --> 00:36:09,239
Speaker 1: you're waiting for your fluid monitoring system to register the changes. Right, yeah, yeah,

627
00:36:09,320 --> 00:36:12,759
Speaker 1: I mean, I mean it needs to be again. It

628
00:36:12,960 --> 00:36:14,840
Speaker 1: comes back to just what a fine balance it is.

629
00:36:15,440 --> 00:36:18,360
Speaker 1: And uh and and therefore you need you need different

630
00:36:18,400 --> 00:36:22,520
Speaker 1: sensors in different places in the human mechanism here, right,

631
00:36:22,680 --> 00:36:26,800
Speaker 1: So the sensation of your thirst being quenched by drinking

632
00:36:26,880 --> 00:36:31,600
Speaker 1: water must be created by a different process altogether the

633
00:36:31,680 --> 00:36:35,440
Speaker 1: author's right quote. Thirst is not quenched by the reverse

634
00:36:35,719 --> 00:36:39,440
Speaker 1: of the process that generates it. Instead, the brain appears

635
00:36:39,560 --> 00:36:44,439
Speaker 1: to somehow detect the intake of liquid. It's usually thought

636
00:36:44,520 --> 00:36:48,120
Speaker 1: that this happens somewhere in the orofaranks in the middle

637
00:36:48,239 --> 00:36:51,760
Speaker 1: part of the throat, and then somehow adjusts the feeling

638
00:36:51,840 --> 00:36:56,080
Speaker 1: of thirst in anticipation of the coming changes in blood

639
00:36:56,120 --> 00:36:59,400
Speaker 1: os molality. So it looks like what happens is that

640
00:36:59,600 --> 00:37:03,360
Speaker 1: your hydrated you drink water. The swallowing of water is

641
00:37:03,400 --> 00:37:07,279
Speaker 1: somehow sensed in the throat, and then these sensations are

642
00:37:07,360 --> 00:37:11,399
Speaker 1: transmitted to the sub formical organ, the SFO, and then

643
00:37:11,480 --> 00:37:15,800
Speaker 1: from there they inhibit thirst generating pathways. And so this

644
00:37:15,960 --> 00:37:19,880
Speaker 1: raises interesting questions how exactly do we sense water intake

645
00:37:19,960 --> 00:37:22,520
Speaker 1: in the throat? This was not well understood at the

646
00:37:22,560 --> 00:37:24,840
Speaker 1: time this paper was written. I actually have come across

647
00:37:24,880 --> 00:37:27,560
Speaker 1: a couple of studies in the years since that we

648
00:37:27,600 --> 00:37:29,080
Speaker 1: can talk about as we go on. We might get

649
00:37:29,160 --> 00:37:30,960
Speaker 1: more into those in the next part of the series.

650
00:37:31,440 --> 00:37:33,920
Speaker 1: Um But at the time, some of the ideas out

651
00:37:34,000 --> 00:37:36,879
Speaker 1: there were, well, maybe it has something to do with temperature.

652
00:37:37,560 --> 00:37:42,440
Speaker 1: Apparently cooling of the throat triggers water intake signals, and

653
00:37:43,360 --> 00:37:46,600
Speaker 1: evidence for this claim would be that research has found

654
00:37:46,640 --> 00:37:51,320
Speaker 1: that cold liquids inhibit thirst faster than warm liquids. I

655
00:37:51,719 --> 00:37:54,360
Speaker 1: haven't tried it myself, but that sounds correct to me.

656
00:37:55,560 --> 00:37:58,440
Speaker 1: Interesting and it would make sense water usually tends to

657
00:37:58,520 --> 00:38:00,960
Speaker 1: cool the mouth in the throat, and that this cooling

658
00:38:01,280 --> 00:38:03,480
Speaker 1: may be used as a rough signal that water is

659
00:38:03,520 --> 00:38:07,839
Speaker 1: coming in. Also, it seems that cooling of the mouth

660
00:38:07,960 --> 00:38:10,040
Speaker 1: on its own, even if it's not water, just making

661
00:38:10,080 --> 00:38:14,440
Speaker 1: the mouth colder can somehow reduce thirst and reduce activity

662
00:38:14,560 --> 00:38:18,680
Speaker 1: of the SFO. Interesting, so you would potentially be able

663
00:38:18,719 --> 00:38:22,360
Speaker 1: to use just like a cooling breath UH technique to

664
00:38:23,200 --> 00:38:25,920
Speaker 1: to to inhibit thirst possibly if you know, if the

665
00:38:25,960 --> 00:38:29,880
Speaker 1: temperature explanation has anything going for it. But there may

666
00:38:29,920 --> 00:38:31,719
Speaker 1: be other things as well. There may be other ways

667
00:38:31,760 --> 00:38:34,600
Speaker 1: of sensing water in the oral cavity, maybe some stuff

668
00:38:34,640 --> 00:38:36,720
Speaker 1: more along the lines of what you were talking about earlier.

669
00:38:36,880 --> 00:38:40,520
Speaker 1: Things could have to do with UH taste sensors that

670
00:38:40,800 --> 00:38:43,960
Speaker 1: that somehow to detect the presence of water through acid

671
00:38:44,040 --> 00:38:47,799
Speaker 1: sensing taste receptors or something, or there could be there

672
00:38:47,840 --> 00:38:51,520
Speaker 1: may be some limited evidence that stretch receptors and osma

673
00:38:51,560 --> 00:38:55,280
Speaker 1: sensors in the stomach might also detect water intake before

674
00:38:55,360 --> 00:38:57,600
Speaker 1: full absorption. But again, at the time of this summary

675
00:38:57,640 --> 00:39:01,560
Speaker 1: in this was just not fully understood. I guess one

676
00:39:01,560 --> 00:39:03,080
Speaker 1: way of looking at it would be that it's it's

677
00:39:03,080 --> 00:39:06,640
Speaker 1: not necessarily like one trigger or one sensor that is

678
00:39:06,960 --> 00:39:09,320
Speaker 1: that is playing a crucial role here. It's more of

679
00:39:09,440 --> 00:39:13,000
Speaker 1: a whole suite of things, that is UM that is

680
00:39:13,080 --> 00:39:16,760
Speaker 1: generating this UM this this understanding of how much water

681
00:39:17,280 --> 00:39:21,360
Speaker 1: has entered the system. Right, But whatever the exact mechanism is.

682
00:39:21,560 --> 00:39:26,239
Speaker 1: It's definitely anticipatory in nature. It's definitely changing your behavior

683
00:39:26,960 --> 00:39:30,000
Speaker 1: before the thing that your behavior is supposed to fix

684
00:39:30,080 --> 00:39:33,680
Speaker 1: has actually changed yet. Wow, Like when you're done drinking

685
00:39:33,719 --> 00:39:36,120
Speaker 1: the glass of water, you're still dehydrated. You're going to

686
00:39:36,160 --> 00:39:38,959
Speaker 1: be dehydrated for another ten to fifteen minutes at least.

687
00:39:39,480 --> 00:39:42,719
Speaker 1: It's it's the kind of excellence in supply chain management

688
00:39:43,280 --> 00:39:46,680
Speaker 1: that technology companies are chasing after. You know, the idea

689
00:39:46,760 --> 00:39:50,680
Speaker 1: that that they want to anticipate the need um and

690
00:39:50,840 --> 00:39:54,000
Speaker 1: and then you know, be able to uh to to

691
00:39:54,120 --> 00:39:57,600
Speaker 1: alter the supply chain um uh, you know, at moment

692
00:39:57,680 --> 00:39:59,879
Speaker 1: to moment to make sure that the need is met

693
00:40:00,280 --> 00:40:04,040
Speaker 1: without wasting water or product or whatever the case may be. Yeah,

694
00:40:04,200 --> 00:40:07,920
Speaker 1: I like it. Okay, there's more anticipation to come. How

695
00:40:07,920 --> 00:40:14,240
Speaker 1: about anticipatory regulation of thirst from eating from food? Because

696
00:40:14,640 --> 00:40:18,279
Speaker 1: when we eat food, thirst appears to be generated in

697
00:40:18,400 --> 00:40:23,319
Speaker 1: anticipation of coming changes to blood osmalality. So why would

698
00:40:23,400 --> 00:40:26,239
Speaker 1: eating food make us need water? Well, first of all,

699
00:40:26,440 --> 00:40:29,120
Speaker 1: fluids are used in digestion. You think about when you

700
00:40:29,200 --> 00:40:32,560
Speaker 1: eat food, you generate saliva you uh, you know, not

701
00:40:32,680 --> 00:40:35,520
Speaker 1: to be gross, but there's a lot of lubrication that

702
00:40:35,719 --> 00:40:39,800
Speaker 1: needs to happen like swallowing requires some water. Oh, I

703
00:40:39,840 --> 00:40:42,319
Speaker 1: mean you have to. You have to to to chew

704
00:40:42,400 --> 00:40:45,319
Speaker 1: up the food and form the bolus that will then

705
00:40:45,400 --> 00:40:48,839
Speaker 1: travel down the throat. I mean, I think we've we've

706
00:40:48,920 --> 00:40:51,360
Speaker 1: covered that on the show before, Like, think about it today.

707
00:40:51,719 --> 00:40:55,360
Speaker 1: Your next meal really focused on everything that's going on

708
00:40:55,520 --> 00:40:58,120
Speaker 1: in your mouth. It's a it's a beautiful chorus of

709
00:40:58,440 --> 00:41:01,960
Speaker 1: disassembly and then rhasson into the right sort of package

710
00:41:02,000 --> 00:41:04,799
Speaker 1: to then make the journey down to the stomach. It's

711
00:41:04,880 --> 00:41:07,880
Speaker 1: really it's like it's beautiful and it's horrible. You can't

712
00:41:07,960 --> 00:41:09,920
Speaker 1: think about it while you're eating, or at least I

713
00:41:10,000 --> 00:41:13,279
Speaker 1: find I can't just think. I mean, have you ever

714
00:41:13,560 --> 00:41:16,360
Speaker 1: thought of more appetizing idea that you're like mouth and

715
00:41:16,520 --> 00:41:20,279
Speaker 1: throat are lubricating the ball of food that you're smashing up.

716
00:41:21,920 --> 00:41:24,120
Speaker 1: But anyway, so that's one thing. But then the other

717
00:41:24,560 --> 00:41:28,279
Speaker 1: half of it is that eating usually increases blood osmalality

718
00:41:28,400 --> 00:41:31,600
Speaker 1: by adding salt and other things to the body. Yes,

719
00:41:32,160 --> 00:41:34,920
Speaker 1: so much salt. So much so the body appears to

720
00:41:35,040 --> 00:41:39,520
Speaker 1: have an anticipatory response to eating that is generating thirst

721
00:41:39,719 --> 00:41:44,279
Speaker 1: before those changes even register. And this thirst that comes

722
00:41:44,360 --> 00:41:47,480
Speaker 1: from eating is known as pran deal thirst. It seems

723
00:41:47,480 --> 00:41:50,840
Speaker 1: to occur before changes in blood osmalality come into effect,

724
00:41:50,960 --> 00:41:54,640
Speaker 1: so UH a lot of animals are observed to drink

725
00:41:54,719 --> 00:41:56,960
Speaker 1: at the same time that they eat, if they're able.

726
00:41:57,480 --> 00:42:01,080
Speaker 1: The mechanism of this anticipatory new real pathways still not

727
00:42:01,239 --> 00:42:05,880
Speaker 1: fully understood, but if pran deal thirst is not sated

728
00:42:06,080 --> 00:42:09,360
Speaker 1: I mentioned this earlier, sometimes animal brains tend to react

729
00:42:09,480 --> 00:42:13,680
Speaker 1: by reducing appetite until water is consumed. UH. This is

730
00:42:13,760 --> 00:42:18,640
Speaker 1: known as dehydration induced stand orexia, but in general dehydration

731
00:42:18,719 --> 00:42:22,800
Speaker 1: will cause animals to restrict their food intake, with some exceptions,

732
00:42:22,840 --> 00:42:25,160
Speaker 1: of course, because some animals, you know, they get their

733
00:42:25,200 --> 00:42:28,960
Speaker 1: water entirely from food and so forth. But dehydration induced

734
00:42:28,960 --> 00:42:33,240
Speaker 1: stand orexia tends to I thought this was interesting reduce

735
00:42:33,440 --> 00:42:38,640
Speaker 1: meal size but not meal number, so UH it might

736
00:42:38,719 --> 00:42:42,040
Speaker 1: not affect how often an animal is willing to eat,

737
00:42:42,160 --> 00:42:45,760
Speaker 1: but how much they eat when they do eat, meaning

738
00:42:45,880 --> 00:42:49,480
Speaker 1: that it probably works by causing an animal to terminate

739
00:42:49,600 --> 00:42:52,759
Speaker 1: feeding behaviors earlier than they would normally each time it

740
00:42:53,000 --> 00:42:56,120
Speaker 1: it has a meal now at the at the end

741
00:42:56,160 --> 00:42:59,719
Speaker 1: of their right up here, the authors acknowledge that UH

742
00:43:00,120 --> 00:43:03,080
Speaker 1: acknowledge some exceptions to the stuff they're talking about. There.

743
00:43:03,160 --> 00:43:06,360
Speaker 1: These generalizations tend to be true for humans and rodents

744
00:43:06,440 --> 00:43:09,760
Speaker 1: and some other animals, but of course they're very different

745
00:43:09,840 --> 00:43:14,400
Speaker 1: ecological niches that will cause variation to these generalizations. For example,

746
00:43:15,280 --> 00:43:18,440
Speaker 1: a lot of grazing herbivores do not seem to experience

747
00:43:18,520 --> 00:43:22,279
Speaker 1: pran deal thirst or or thirst related to eating, you know,

748
00:43:22,360 --> 00:43:25,239
Speaker 1: because they eat all day, but they only drink drink

749
00:43:25,280 --> 00:43:28,440
Speaker 1: water a few times a day. And then they're very

750
00:43:28,520 --> 00:43:32,320
Speaker 1: different kinds of animals like amphibians that don't technically drink

751
00:43:32,480 --> 00:43:36,040
Speaker 1: at all, like many amphibians just absorb water through their skin.

752
00:43:36,920 --> 00:43:39,000
Speaker 1: We've talked about amphibians before in the show and about

753
00:43:39,040 --> 00:43:41,800
Speaker 1: how the you know, they're how delicate their place in

754
00:43:41,840 --> 00:43:43,880
Speaker 1: the environment can be. And this is this is part

755
00:43:43,920 --> 00:43:45,840
Speaker 1: of it. It's like if if I'm in the environment,

756
00:43:46,200 --> 00:43:49,680
Speaker 1: i am drinking it, I am breathing it. Uh, and

757
00:43:50,040 --> 00:43:53,759
Speaker 1: my skin is the is the barrier through which all

758
00:43:53,800 --> 00:43:57,920
Speaker 1: this takes place. Yeah, very different relationship to one's environment,

759
00:43:58,160 --> 00:44:01,200
Speaker 1: very very different kind of chemist of being for the

760
00:44:02,000 --> 00:44:04,640
Speaker 1: for the amphibian, I recall it's been a while, but

761
00:44:04,719 --> 00:44:08,800
Speaker 1: I recall reading a funny article about terrestrial toads that

762
00:44:08,840 --> 00:44:12,920
Speaker 1: would primarily do water absorption through their pelvic regions, so

763
00:44:13,040 --> 00:44:16,120
Speaker 1: they sort of like like thrust their lower bodies and

764
00:44:16,560 --> 00:44:20,160
Speaker 1: bellies into any surface that's wet while they're while they're

765
00:44:20,160 --> 00:44:23,160
Speaker 1: hanging out in water absorption mode. All right, we're gonna

766
00:44:23,160 --> 00:44:24,839
Speaker 1: go ahead and close out this episode, but we will

767
00:44:24,880 --> 00:44:27,520
Speaker 1: be back for a third thirst episode. We have a

768
00:44:27,560 --> 00:44:31,080
Speaker 1: lot of additional information we want to get to. Don't worry,

769
00:44:31,120 --> 00:44:33,840
Speaker 1: there will be parasites in it. Uh. So it should

770
00:44:33,840 --> 00:44:36,560
Speaker 1: be uh, it should be a grotesque a good time.

771
00:44:37,000 --> 00:44:39,400
Speaker 1: And of course in the meantime, right in, let us

772
00:44:39,440 --> 00:44:42,239
Speaker 1: know your thoughts on water. And all of you are

773
00:44:42,400 --> 00:44:45,880
Speaker 1: water drinkers. You consume water one way or another or another.

774
00:44:45,960 --> 00:44:47,759
Speaker 1: And I imagine you have some thoughts on all of this.

775
00:44:48,200 --> 00:44:50,160
Speaker 1: Do you do you love drinking water? Do you hate

776
00:44:50,200 --> 00:44:53,960
Speaker 1: drinking water? Um? Is there? What are your thoughts on

777
00:44:54,080 --> 00:44:58,600
Speaker 1: the consumption of cold water versus hot water? Um or

778
00:44:58,680 --> 00:45:01,520
Speaker 1: maybe prefer the lukewarm wa water. I mean, I guess

779
00:45:01,520 --> 00:45:03,759
Speaker 1: they're factors we didn't even get into. You know, like

780
00:45:03,880 --> 00:45:06,279
Speaker 1: sometimes cold water can be a sensitive on the teeth

781
00:45:06,280 --> 00:45:08,719
Speaker 1: and gums. Uh, the same can be said for for

782
00:45:08,840 --> 00:45:11,239
Speaker 1: hot water as well, So I don't know, perhaps you

783
00:45:11,280 --> 00:45:14,040
Speaker 1: have thoughts on that. Have you never drunk water? Have you?

784
00:45:14,520 --> 00:45:19,880
Speaker 1: Are you a creature that only absorbs water from chicken nuggets? Oh,

785
00:45:20,000 --> 00:45:24,320
Speaker 1: the chicken chicken nugget water? Yes? Well, anyway, right, and

786
00:45:24,640 --> 00:45:27,720
Speaker 1: let us know it's all fair game. In the meantime,

787
00:45:28,200 --> 00:45:30,399
Speaker 1: as usual core episodes of Stuff to Blow Your Mind

788
00:45:30,560 --> 00:45:32,640
Speaker 1: Tuesdays and Thursdays and the Stuff to Blow your Mind

789
00:45:32,680 --> 00:45:35,920
Speaker 1: podcast feed We have a listener mail on Monday, Artifact

790
00:45:35,960 --> 00:45:37,920
Speaker 1: on Wednesday, and on Friday we do Weird how Cinement

791
00:45:37,960 --> 00:45:40,600
Speaker 1: at our time, just that most serious matters aside and

792
00:45:40,719 --> 00:45:43,480
Speaker 1: just talk about a strange film. Huge thanks as always

793
00:45:43,520 --> 00:45:46,960
Speaker 1: to our excellent audio producer Seth Nicholas Johnson. If you

794
00:45:46,960 --> 00:45:49,120
Speaker 1: would like to get in touch with us with feedback

795
00:45:49,200 --> 00:45:51,479
Speaker 1: on this episode or any other, to suggest a topic

796
00:45:51,560 --> 00:45:53,800
Speaker 1: for the future, just to say hello, you can email

797
00:45:53,880 --> 00:45:57,080
Speaker 1: us at contact at stuff to Blow your Mind dot com.

798
00:46:04,800 --> 00:46:07,280
Speaker 1: Stuff to Blow Your Mind is production of I Heart Radio.

799
00:46:07,640 --> 00:46:10,000
Speaker 1: For more podcasts my heart Radio, visit the i heart

800
00:46:10,040 --> 00:46:12,759
Speaker 1: Radio app, Apple Podcasts, or wherever you're listening to your

801
00:46:12,800 --> 00:46:13,440
Speaker 1: favorite shows.