0:01 hi every Dr Mike here in this video
0:04 we're going to make sense of acids bases
0:08 and buffers finally now let's take a [Music]
0:14 [Music]
0:17 look so to begin we need to understand a
0:20 couple of things first thing is this
0:22 your body is filled with ions these are
0:25 charged atoms or elements examples of
0:29 ions include sodium and pottassium and calcium
0:30 calcium
0:32 and also hydrogen but there's others
0:34 there's bicarbonate there's chloride
0:36 there's magnesium regardless they're
0:39 charged atoms or elements they all play
0:42 roles in the body for example sodium and
0:43 potassium really important for nerve
0:46 conduction calcium muscle contraction
0:49 and hydrogen ions what's that important
0:54 for H well this is the question for the
0:55 day right
0:58 because if I were to measure your sodium
0:59 concentration in your blood it's going
1:03 to be about 140
1:05 Mill but if I were to measure the
1:07 concentration of hydrogen in your blood
1:14 0.00004 Millar there's a huge difference
1:17 hydrogen concentration really low and
1:19 this is important because we need to
1:22 maintain a low concentration of hydrons
1:25 because it's super reactive and you
1:26 might think but it's charged just like
1:28 all the others why is it so reactive
1:30 think about the periodic table right
1:32 right hydrogen helium lithium burum
1:34 boron carbon hydrogen's the first one
1:36 it's really tiny it's simp it's
1:39 basically if you look at it in its
1:43 ionized form it is just a proton and
1:45 then as you move through you have bigger
1:48 and bigger uh uh elements like you get
1:50 to sodium
1:53 right which is going to be big with its
1:55 little charge and then you have
1:57 pottassium which is even bigger as an
2:01 atom with its little charge so hydrogen
2:03 right which is just a charge compared to
2:07 the others its size to charge ratio
2:09 right huge charge compared to its size
2:12 so it's super reactive which means it
2:13 goes around the body trying to steal
2:15 electrons from things like proteins and
2:17 it can damage the proteins and a whole
2:19 body is made out of proteins they form
2:21 the structural components of our body
2:23 but also the functional like enzymes you
2:26 don't want to damage the proteins so we
2:28 need to maintain these low hydrogen ion
2:30 concentrations and as you know from my
2:33 previous videos we measure hydron
2:38 concentration not like this but as pH so
2:40 how do we maintain our hydron
2:42 concentration as being low well the
2:44 first thing is we need to talk about how
2:46 we even make hydrogen ions where do
2:49 these hydrogen ions come from great
2:53 question Dr Mike so we need to talk
2:55 about acids acids are what produce
2:57 hydrogen ions if I were to draw up the
3:00 most basic or I should say not basic I
3:01 need to be careful cuz we're talking
3:04 about acids and bases the most simple
3:08 way to write an acid I could write ha so
3:10 let's say that is an
3:14 acid that's an acid what acids do by
3:17 definition is they donate hydrogen ions
3:20 right so this acid will donate a
3:23 hydrogen ion now as you know a hydrogen
3:25 ion can also just be called a proton
3:27 they're synonymous so keep that in mind
3:30 if I were to donate that hydrogen ion
3:34 what am I left with I'm left with the A
3:35 and it's going to be negative cuz that's
3:37 neutral so the positive and negative
3:39 charges balance out if I steal the
3:41 positive there's the negative what we
3:43 call this is the conjugate
3:45 conjugate
3:48 base now this is where we can introduce
3:50 bases I said the definition of an acid
3:53 is it donates hydrogen ions the
3:56 definition of a base is that it absorbs
4:00 or mops up hydrogen ions which means
4:02 this equation can effectively or
4:03 theoretically go in the opposite
4:05 direction where the base mops up the
4:09 hydrogen and produces the acid again
4:11 very important
4:13 concept what determines
4:15 determines
4:18 how an whether an acid goes in that
4:20 direction or whether the base mops it up
4:22 and goes in this direction well to
4:23 understand that we need to draw up some
4:26 actual physiological or biological acids
4:28 that we have in the body there's a whole
4:29 bunch I'm going to drop some some
4:34 important ones so we have hydrochloric
4:38 acid hydrochloric acid we
4:41 have H2
4:44 P4 Nega which we call dihydrogen
4:51 phosphate or phosphoric acid we can have
4:55 h23 which we call carbonic acid we can
4:57 have like you've probably heard of amino
5:00 acids and fatty acids and lactic acid
5:02 and pyruvic acid so there's a whole
5:05 bunch let's talk about amino acids just
5:07 very quickly amino acids
5:10 so amino acids are really really
5:12 interesting remember an acid can donate
5:15 a proton so if I want to draw up an
5:19 amino acid again a simple version
5:22 carbon hydrogen there's this functional
5:24 side group that has that can change
5:26 that's what determines the flavor or the
5:28 type of amino acid that we have but we
5:33 also have a a carboxy end right this is
5:35 what we call the C Terminus that's the
5:40 caroal end and we have an aan Terminus
5:42 which we call the N terminal right so we
5:45 got the N terminal aan end C terminal
5:49 carboxy and have a look at it right this
5:50 is really
5:52 interesting this C
5:56 Terminus can donate the hydrogen onon
6:00 into the solution and if it does
6:10 produce Co Nega so it's a it's an amino
6:13 acid because it can donate a proton
6:15 beautiful it can also go in the opposite
6:18 direction right and be reprotonated
6:22 bring that prot proton back wonderful
6:24 this side can do the same thing this
6:28 side can take on hydrogen ions and if it
6:32 does it becomes
6:37 NH3 positive or it can release a hydron
6:41 from mh3 positive and bring it back to
6:44 nh2 so you've actually got two ionizable
6:47 groups on amino acid sort of acting as
6:48 and I haven't defined this yet but as
6:51 like a double buffer so let's write this
6:54 down here let's write the way I'm going
6:56 to write this down is like this you've
7:02 got an amino acid with the C terminal or
7:05 you've got an amino acid with its
7:11 protonated amine terminal all acids so
7:12 since they're all acids what do they do
7:15 they all disassociate to release hydrogen
7:16 hydrogen
7:19 ions so that's easy so we know that
7:21 because they're
7:23 acids but what do they produce they
7:25 conjugate base so what's the conjugate
7:28 base I remove hydrogen ion I'm left with
7:31 chloride ion I remove a hydrogen from
7:33 here I've only left with one
7:37 hydrogen one phosphate and four oxygen
7:38 but two
7:41 negative so hydrogen
7:44 phosphate here I'm left with a hydrogen
7:46 a carbon and three oxygen and negative
7:47 that's called
7:51 bicarbonate this the carboxy end I'm
7:56 left with Co negative and here I'm left
8:03 these are the conjugate bases from the
8:06 acid all right here's the thing I asked
8:10 the question you can theoretically say
8:11 that because a base can bind to a
8:14 hydrogen ion to produce an acid but an
8:17 acid can disassociate into hydrons and
8:19 the conjugate base what determines which
8:22 direction it goes all right that's
8:24 determined by two important
8:26 things the
8:29 ph and the pka
8:34 the ph and the pka related terms the pH
8:37 is the concentration of hydrogen ions in
8:39 the immediate solution that it's in
8:41 right we know in the body it should be at
8:42 at
8:47 7.4 that's the pH the pka is the value
8:51 that each acid has that tells you how
8:55 likely it is to donate its hydrogen ion
8:59 its proton in a particular pH you might
9:01 go oh what does this even mean all right
9:03 let's think about it like this right
9:06 let's let's say let's just write up the
9:09 the basic sorry the simple form of an acid
9:11 acid
9:15 ha reversibly gives us hydrogen ions
9:17 plus the conjugate base and let's write
9:19 it on a
9:21 seesaw or in the US what do you call it
9:22 a TA
9:28 tot now we know that the pH of the
9:30 solution should be
9:34 7.4 right now if the
9:36 pka the
9:40 pka which is the value that's given to
9:42 the acid to tell you how likely it is to
9:44 donate its hydrogen ion if that's the
9:46 same as the
9:49 pH it simply tells you that if that's
9:51 the same as that it's balanced it's
9:53 going to go equal in that direction as
9:56 it is in that direction so it's as
9:58 likely to donate protons as it is to
10:00 bind them up
10:02 that's actually what we call a buffer a
10:06 buffer is when the pka is as close as it
10:09 possibly can be to a pH to the pH of the
10:13 solution and it can release protons when
10:17 needed and bind them up when needed so
10:19 that is a good buffer excuse me a good
10:23 buffer is when the pka and the pH are
10:26 close together when the ph and the PK
10:28 they'll never be exactly the same at
10:30 least not biologically but when they're
10:32 as close as possible to each other that
10:37 makes a really good buffer cuz what a
10:39 buffer does is it resists drastic
10:41 changes in PH I said to you we've got
10:43 low numbers of hydrogen ions we want to
10:46 keep it low so if for whatever reason
10:48 the hydrogen levels accumulate in our
10:51 blood what do we do all good we mop it
10:53 up so it's not available what if the
10:56 hydr levels go too low I know that's
10:58 also a problem let's release some
11:00 buffers are perfect CU they can go in
11:04 each Direction now if an acid has a PKA
11:06 that's less than the
11:10 pH so let's say the pka is 6.1 that's
11:13 obviously less we've now just moved it
11:14 from being centered in the middle and
11:17 nice and balanced to on this side which
11:20 means this whole thing goes like that
11:23 now if it goes like that what goes up
11:28 the hydrogen ions go up so if the pka is
11:30 lower than the
11:34 pH you produce more hydrogen ions you
11:36 produce more hydrogen ions right it's
11:39 more likely to go in that
11:41 direction if the
11:44 pka is higher than the pH you probably
11:46 know what's going to happen in this case
11:48 let's say
11:51 8.1 it's weighted in this direction that
11:55 side goes up so you form more acid you
11:58 mop up more hydron so that goes down
12:00 right makes sense
12:03 perfect so what determines How likely it
12:05 is to disassociate or not has to do with
12:07 both the pH of the environment that it's
12:09 in because that can change too right
12:11 that can change as well so for
12:14 example if you've got an
12:17 acid that has a
12:19 pka of
12:23 6.8 and we know the pH of the body is
12:26 7.4 but let's just say the pH changed
12:33 7.25 right not a good number but let's
12:36 say simp it's closer to the PK it's now
12:39 becoming a better buffer it's now this
12:42 assd has now become a better buffer
12:44 because it's closer the ph and the p k
12:46 are closer I'll give you an example of
12:48 that in a sec all right I promise I'll
12:49 give you an examp a good biological
12:53 example of that in a second all right so
12:56 here's the thing hydrochloric acid its
13:00 PKA is like negative six or something
13:03 it's all the way down here which means
13:07 it goes well up which means this acid
13:10 hydrochloric acid it basically will only
13:12 go in One Direction it will only
13:15 disassociate to produce hydrogen ions
13:17 and chloride so it's not a you can't use
13:18 it as a buffer it won't go in the
13:20 opposite direction hydrochloric acid is
13:24 what we call a strong acid hydrochloric
13:27 acid is what we call a strong acid
13:30 strong acids
13:32 basically are more likely to fully
13:35 disassociate into its hydrogen and and
13:37 the conjugate base right but you can
13:39 have what's called a weak acid all of
13:42 these are weak acids weak
13:45 acids let's write this down all of these
13:48 are called weak
13:50 acids weak
13:54 acids have the pka and the pH closer to
13:56 each other so they can go in both
13:58 directions and they're more likely to so
14:00 which means all of these can act as
14:03 buffers and this leads us to our next
14:08 Point buffers so the body has three
14:11 important chemical buffers they all by
14:13 definition buffers have to be weak acids
14:16 so the three chemical buffers we've
14:18 actually drawn up here the three
14:36 buffer and the protein buffer also know
14:39 as the amino acid buffer these are the
14:41 three most important chemical buffers of
14:44 the body let's go through them so let's
14:47 start with phosphate
14:53 right the pka of dihydrogen phosphate I
14:54 think it's around about
14:58 6.8 it's relatively close to the pH it's
15:00 actually the of all three it's the
15:03 closest PKA to the pH in the body which
15:06 means theoretically it's the best buffer
15:10 but the problem with phosphate is that
15:12 it's mostly if that's a cell you got the
15:14 extracellular fluid and the
15:16 intracellular fluid phosphate is mostly
15:18 in the
15:23 intracellular fluid H2 P4 Nega not much
15:26 in the extracellular fluid so phosphate
15:27 is a
15:32 good intracellular fluid
15:35 buffer but not great as an extracellular
15:37 fluid buffer the other thing is this
15:41 right now the kidneys you filter blood
15:43 right so if I were to draw up a
15:46 kidney let's draw up a kidney
15:49 here you know that you've got with the
15:52 kidney the
15:54 cortex that's the outside here and the
15:57 medala in the cortex you've got all
15:59 these strange looking what look like
16:01 Pac-Man heads with worm
16:04 bodies which we call nephrons that's a
16:08 nefron there's 1 million per kidney they
16:10 filter the blood so the renal artery
16:12 that comes in will enter and will Branch
16:14 multitude of times and finally you've
16:17 got these terminal branches that we call
16:20 afren arterials that enter this nefron
16:22 and that's what filters the blood in a
16:24 million of them right so let's make this
16:27 bigger and just have a quick
16:30 look if here's a
16:41 body
16:44 right and you've got the blood vessel
16:47 entering turns into a capillary bed
16:50 called the glus and then it leaves so
16:53 blood enters blood leaves this is where
16:56 stuff gets filtered there's a mem a
16:58 number of membranes here that can filter things
17:00 things
17:02 this is what we call the renal tubu and
17:05 the renal tubu has renal tubular cells now
17:07 now
17:10 importantly the renal tubule and the
17:13 tubular cells increase the concentration
17:17 of phosphate right they increase the
17:25 tubules they also the pH changes you're
17:28 starting to make urine here right so the
17:31 pH drops and as the pH drops in this
17:33 case it's getting closer to the pka of
17:37 phosphate making it a better buffer so
17:38 effectively in the renal tubules and the
17:42 tubular cells phosphate becomes a really
17:45 important buffer all right so there we
17:46 go for
17:49 phosphate let's skip bicarbonate for a
17:51 second let's talk about
17:53 proteins proteins are really important
17:56 buffers because proteins are everywhere
17:59 so really abundant inside cell
18:01 so a really important
18:03 intracellular fluid
18:07 buffer and most of the body's buffering
18:08 like 60 to
18:12 70% of the body's buffering happens
18:15 inside of the cells and most of that is
18:19 because of proteins so it's the most
18:27 buffer but it's not the most important
18:29 strangely enough how does it work as a
18:31 buffer we highlighted this earlier but
18:34 let me just reiterate some points right
18:37 you've got an amino
18:40 acid with its functional side group it's
18:43 got its carboxy end and it's got
18:50 its amine end if the solution becomes
18:53 too acidic so too many hydrons
18:56 accumulate in the cell for example or in
19:00 the body we want to it out right we want
19:02 to mop them up so the hydrogen can bind
19:04 to the aan
19:09 end and what do we end up producing NH H3
19:11 H3
19:14 positive brilliant this amino acid just
19:18 buffered out the excess hydrogen ions by
19:20 binding them to the amine chain the
19:24 amine group what if we don't have enough
19:27 hydrogen ions in the blood easy the
19:32 carboxy end will donate hydrogen
19:36 ions and what do we end up getting Co
19:37 Co
19:41 negative so now Vice Versa that can
19:42 happen in the opposite direction they
19:45 can bind back and that can be released
19:48 back so effectively proteins or with
19:50 their amino acids are really good
19:53 buffers because they've got two
19:55 ionizable side groups here that can
19:57 donate and release protons depending on
20:01 the pH of the solution and its own PKA
20:03 and here's the other thing the side
20:06 chain here can be basic or acidic
20:08 meaning there's amino acids that in
20:11 addition to having the C Terminus have
20:13 another carboxy and here as its
20:16 functional group which means it can act
20:19 to donate or release protons or you can
20:20 have amino acids that have an amine
20:22 group as its functional group and can do
20:24 the same thing so obviously what I'm
20:25 saying is amino acids can be really great
20:27 great
20:29 buffers but they're not the most
20:30 important the most important are the
20:33 bicarbonate buffers right so now we need
20:37 to talk about the bicarbonate buffer
20:39 system here's the thing about the
20:41 bicarbonate buffer system we've drawn it
20:43 out sorry we've drawn it out here but
20:46 it's a bit more than this think about
20:49 your body you take in oxygen you take in
20:52 nutrients like glucose and you make
20:54 energy ATP what's the byproduct of that
20:57 metabolism it's carbon dioxide so all
20:59 the cells of your body produce what do
21:03 they produce they produce carbon dioxide
21:05 now this carbon dioxide needs to get to
21:07 our lungs to be breathed out it's the
21:09 exhaust fumes of the body but to do that
21:10 it needs to jump into the blood to get
21:13 transported to the lungs you know that
21:16 most of the blood is water so that
21:18 carbon oxide needs to bind to water in
21:21 our blood what does it produce what does
21:25 it produce well it produces two
21:31 hydrogen one carbon and 1 2 3 oxygen
21:35 wait a minute that is carbonic acid
21:37 which also means that it's going to
21:39 split apart cuz like I said acids hate
21:42 themselves they split apart to produce
21:44 hydrogen ions
21:47 and let's get rid of that
21:51 bicarbonate ions and it's reversible cuz
21:55 it is a buffer all right why is it such
21:58 an important buffer I'll tell you why because
21:59 because
22:00 unlike these other
22:03 buffers which we call nonvolatile
22:06 buffers this buffer the bicarbonate is a
22:08 volatile buffer what that means is part
22:12 of the equation produces a gas that can
22:13 be breathed out that's why it's called
22:15 volatiles you can actually play with
22:19 around with the concentration of hydrons
22:22 through breathing right have a look at
22:25 this right have a look I love
22:28 this if you increase the amount of carbon
22:29 carbon
22:33 dioxide in your blood it will bind to
22:36 the water produce carbonic acid which
22:39 will split itself apart to produce
22:42 hydrogen ions and your blood becomes
22:44 more acidic because of the concentration
22:48 of hydron go up so effectively increase
22:50 carbon dioxide in the blood increase the
22:53 amount of acid or hydron in the blood
22:55 but because it's reversible hydrogen
22:58 ions combind to B carbonate and produce
23:00 more carbon dioxide that we can breathe out
23:01 out
23:04 so the way You' think about it is in
23:08 both directions right like this
23:09 Something's Happened in my body to
23:11 produce too many hydrogen ions don't
23:15 worry by carbonate will bind with it
23:18 produce carbonic acid which will split
23:20 apart and produce carbon dioxide and we
23:22 breathe it out when you breathe that
23:25 carbon dioxide you breathe out acid
23:27 effectively cuz think about it if I
23:29 don't have if if I
23:31 hyperventilate I breathe away all my
23:34 carbon dioxide it goes down less carbon
23:36 dioxide to bind with water less carbonic
23:39 acid less hydrogen
23:42 ions now again you might be thinking why
23:45 is it the most important buffer because
23:48 of this this end of the equation is
23:50 dealt with by the
23:53 lungs and because right now I can either
23:55 hold my
23:57 breath what am I doing when I do this my
23:59 carbon dioxide levels go go up if they
24:03 go up it produces more hydrons or I can
24:06 hyperventilate and get rid of it I can
24:08 change the pH of my blood in the short
24:12 term through breathing and so lungs can
24:15 change the pH in the short term
24:17 term
24:20 brilliant on this side of the
24:22 equation the kidneys can play around
24:24 with your
24:27 bicarbonate and you can either make more
24:29 bicarbonate reabsorb more bicarbonate or
24:32 pee out more bicarbonate right and that
24:35 can change your blood pH but that takes
24:38 longer hours to days so this is a longer term
24:40 term
24:42 control so have a
24:46 look we can control the pH of our blood
24:49 through our lungs and our kidneys in the
24:51 short term and long term which makes it
24:54 an extremely important buffer because it
24:58 can fine-tune the pH of our blood so the
25:00 three buffers of the body phosphate
25:03 bicarbonate and proteins most important
25:05 bicarbonate in a future video we're
25:09 going to focus on this buffer in
25:11 isolation and talk about all the
25:14 different types of acidosis and
25:16 alkalosis I'm Dr
25:19 Mike hi everyone Dr Mike here if you
25:21 enjoyed this video please hit like And
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25:35 todorovich d m i k t o d o r oov i c
