we're going to talk aboutantidiuretic hormone. and you can see i've alreadystarted drawing for this video. and the main reason is becausei'm not a great drawer, and i wanted to make sure thateverything was pretty clear. and so i drew out on oneside the pituitary gland
and on the other the brain. and so antidiuretichormone-- i underlined adh because that's usuallywhat it's called. people call it adh.
sometimes people callit vasopressin as well. actually, vasopressin isgood because it's useful. you can see "vaso" kind ofrefers to blood vessels, and "pressin" kind of squeezingdown on blood vessels. it gives you a clue as towhat the hormone is doing. so i've drawn for youthe hypothalamus here. also, right belowit, this would be kind of the infundibulum,kind of the neck. and at the verybottom, the pituitary.
so this is the actualpituitary down here. and there's a frontand back to this. and the front, facingforward closer to the eyes, would be the anterior pituitary. so that'd be over here. and back here, this lobe wouldbe the posterior pituitary because it's a littlebit further back. and since we'renaming stuff, let me just go aheadand round it out.
this right here isactually the optic chiasm. it has to do with vision. so i'm just going towrite optic chiasm so you know whatwe're talking about. and the only reasoni even bring that up is because just above it--let's say in this area-- just above it. and if i was to draw itover on my little diagram-- that'd be maybe right there--is what's called the "supra"--
s-u-p-r-a-- supraoptic nucleus. and nucleus here justrefers to a collection of nerve cell bodies, notthe nucleus we usually think of-- meaning not theone where it's sitting inside of a cell and kind ofdirecting the flow of traffic in the brains of the cellin a way of saying it. but here the nucleus isactually just a collection of little nerve cell bodies. and i'm actually justgoing to draw two,
but you know there'sactually many more there. this is just fordiagram purposes. and actually, if i was todraw the rest of this nerve, you would actuallygo all the way down. and this is actually beginningto share with you some of the cool aspects of thishypothalamus and the posterior pituitary. you can see that, basically,these nerve cells start in one spot, andthey go all the way
down to the posterior pituitarythrough that infundibulum. this is how the hypothalamusand posterior pituitary are connected-- through nerves. and these nerves are actuallyfull of the hormone adh. so we've alreadytalked about the fact that this is related to adh,but now you can see exactly how. adh is actually beingmade in these nerve cells. and it's actuallysitting here waiting for the right moment forthese nerves to release it.
and this adh is actuallya small protein. it's nine amino acids long. so it's actually pretty small. this is adh. nine amino acids. so it's pretty teeny,and it's a hormone. and if you know it's anamino acid-based hormone, you can think of it as apeptide or a protein hormone and distinguish it fromthe steroid hormones.
so this is how adh is made. it's made in these nerve cells. and the next thing to talkabout is how it's released. and so if you have, let'ssay, a little capillary bed in here with littlearterials and capillaries coming together into littlevenules on this side, what happens is that, whenthere's a trigger-- and actually, maybei should write that in a very bold color.
let's say red. that's my favorite bold color. when there's a trigger,these nerve cells right here are going to fire off their adh. they're going torelease all that adh, and it's going to dumpright here into this area where all the capillaries are. and of course, theflow of blood is going to carry all thatadh into the little vein--
and let me draw thevenule and the vein-- and basically, take itto the rest of the body. so this is how adhactually gets released out of the nerve cells that livein the supraoptic nucleus and gets out to the body. it basically does it by dumpinginto that posterior pituitary and getting picked up byall those little capillaries and venules. so i guess the next issue is tofigure out what is the trigger?
so what is the trigger forthis little supraoptic nucleus that i've drawn here? so let's talk about that. let me make some space. there. now, we've got aclean bit of canvas. so let's talk about thetriggers that our body uses to know when to fire offthat adh to get it released. the main trigger-- and thisis probably the one trigger
that you want to take away. if you're going toforget everything else, try to remember this one. the main trigger is going tobe high blood concentration. and the way we think about bloodconcentration is in osmolarity. let me write that down. what osmolarity refers to is,if you took all the solutes that are floating aroundin the blood-- so that includes everythingfrom protein to sodium
to potassium, everythingthat is going to drag water into the blood vessels--if you combine all that, then what is your total bloodconcentration going to be? and you can almostthink of it as a meter. so let me draw it for you. like a little meter here. on one side, you've got--let's say something like that. and on one side,let's say you've got 260, and onthe other side 320.
and this is just concentrations. so 280 and 300. and this is osms per liter. and actually, theseare the units here. so osmolarity as measuredin osms per liter. so this is the concentration. and what you wantto do is you want to really stay inthis area right here. this is kind of your green zone.
this is where the body likesto be, generally speaking. and if it's here, ifit's in this area, or if it's in thisarea, then that's where the body is not too happy. and so for example, let's sayyou're in this first zone. this would meanthat your body is noticing that theblood is too dilute. and if it's on thisside, your body's noticing that it's too salty.
the body is saying thatthe blood is too salty. and so in thiscase, if you have, let's say-- like isaid-- a meter down here, if the needle isfalling in this area, then that's going to be atrigger for adh release. so that's the first triggerthat we can talk about. in fact, why don'ti even go back up and add that to our diagram? so i'm going to putthat into our diagram
so that we can seeit very clearly as being one of the triggers. so let's imagine you haveright here a little nerve cell. and i'm going to draw it thisway purposefully because we actually don't know wherethese little osmoreceptors are. all we know is thatthey do a fantastic job, but we don't know exactlywhere these osmoreceptors are. and this is my littlediagram that i drew before. and you can now think, if theosmoreceptor is telling you
that it's over there,then that's a problem. and in fact, why i don'ti even go one step further and label this asmy osmoreceptor? so if my osmoreceptor is setto tell me that it's too salty, that is one ofthe signals that's going to trigger adh release. ok. so now, what's thesecond trigger? what's another reasonwhy we might release adh?
low blood volume. think about that for a second. how in the world wouldyour body even know that the bloodvolume is too low? well, let's go back to basics. let's go back to the heart. that's where i like tobegin because that's how i always think about it. just very simply, whatis going into the heart,
and what's coming out? well, we know we haveblood vessels-- large ones, in fact, large veins--dumping into the heart. so we have the superiorand inferior vena cava. this is the superior venacava-- this is a large vein-- and this is theinferior vena cava. these aren't theonly large veins, but these are twoexamples of large veins. and we also havethe right atrium.
so we have a coupleof spots here that are in theblood vessels where we might have littlenerve endings. so nerve endingsin these areas are going to start recognizingwhen the blood volume is low. because, remember,the venous system-- this is kind of a stretch-- thevenous stretch from something we talked about a long time ago. the venous systemis actually going
to be a large volume system. so if there's ever adecrease in the volume, that would be one of thebest places to figure it out. so information in the walls-- sobasically, these nerve fibers, rather, in thewalls of the vessels are going to be less stretched. and they're going to say, well,why are we less stretched? and the answer is that there'sactually less blood volume. so when they're less stretched,they're going to send a signal
and say, hey, something's up. we have less bloodvolume, and i think the brain needs toknow about that. so that's how a signal gets sentall the way up to the brain. and actually, i candraw that in as well. so let's put in alittle receptor here. and now, these are going togo down and sense low volume from those receptorsin the large veins and the right atrium.
now, what's another trigger? you can see there are alot of different triggers. i'm putting upone after another. let's put anothertrigger up there. what's another reason whyadh would be secreted? well, maybe a decreasein blood pressure. now, we know thatthe veins tell us a lot of informationabout volume. so it might extend thatthe arteries can tell us
about pressure. and you might recallfrom another video where we talked aboutbaroreceptors that this is a fantastic way to getinformation about pressure. so let me draw some ofthose baroreceptors. and baroreceptor justrefers to pressure receptor. we have baroreceptors that arein the aortic arch right there. and we also havebaroreceptors that are in the carotidsinuses on both sides.
so these baroreceptors are goingto recognize when the blood pressure is starting to go low. and they're goingto send a signal up to the brain tosay, hey, again, we need to do something about this. our pressure is low. so that's anothersignal up to the brain. and that we candraw it right here. we could say, ok.
maybe something like this. and that would be asignal about low-- let's write thathere-- low pressure. so now we've got signals abouthigh osmolarity, low volume, low pressure. are there any other signalsthat we can think of? one more jumps to mymind-- angiotensin 2. remember, angiotensin2 is actually part of the whole ras system--the renin-angiotensin-- or i'll
just write at--aldosterone system. and so angiotensin 2 is actuallygoing to be another trigger. so you can actually imaginethrough a blood vessel, and you might havea nerve nearby. and this is going to triggerright here this molecule of angiotensin, which haseight little amino acids. it's going to be asignal to that nerve that it needs to let the bodyknow-- or the brain know, rather, that pressures are low.
this is another signal. and let me just write thatup here in our picture. another signal couldbe something like this. maybe right here. and the exact locationthat i'm drawing is actually justkind of arbitrary, but the idea is thatyou have angiotensin 2 having effects onthe brain as well. so this little moleculeis going to come and let
the brain know that, hey,even the kidneys are trying to do something aboutthe blood pressure. and it would be great ifthe brain got involved in releasing someadh, if needed. so these are thedifferent triggers. and like i saidin the beginning, probably the main oneyou want to think about--
Diabetes Inspidus,as far as adh is concerned--is this osmoreceptor. this is really themost important one
because everything elseis secondary to that. that is definitely themajor function of adh.
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