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CO2 + H2O H2CO3 H+ + HCO3 - H2CO3 CO2 + H2O H2CO3H
+ + HC
O3 - H
2 CO
3H+ + HCO3 - H2CO3
CO
2 +
H2O
H
2CO
3
H+
+
HC
O3
-
H
2CO
3C
O2
+ H
2O
H2C
O3
H
+ +
H
CO
3 -
H2C
O3
CO
2 + H2 O
H2 C
O3 H
+ + HC
O3 - H
2 CO
3C
O2 + H
2 O H
2 CO
3CO2 + H2O H2CO3 H+ + HCO3 - H2CO3
A Buffer System
An Introduction to theBicarbonate Buffer System
By Noel Ways
CO2 + H2O H2CO3 H+ + HCO3 -
Equilibrium
When chemical reactions are in equilibrium, the rate of reaction is the same in both directions. Equilibrium does not mean that the concentrations are the same, only that the rate of reactions is pro-ceeding at the same rate ( ) in both directions.
However, when a system is at equilibrium, and then the concentration on one side of the reaction changes, equilib-rium will be disturbed. In this example as the CO2 concentration increases, there will be more CO2 to react with H2O, and therefore the reaction will be proceed to the right and more H2CO3 will be produced. This will continue until equilibrium is reestablished.
Likewise, if the concen-tration on the other side of the reaction increases, then the rate of reaction will shift in the other direction until equalibrium is reestab-lished.
CO2 + H2O H2CO3
CO2 + H2O H2CO3
CO2 + H2O H2CO3
CO2 + H2O H2CO3
CO2 + H2O H2CO3
CO2 + H2O H2CO3
CO2 + H2O H2CO3
CO2 + H2O H2CO3
CO2 + H2O H2CO3 Page 2
CO2 + H2O H2CO3 H+ + HCO3 -
CO2 + H2O H2CO3 H+ + HCO3 -
CO2 + H2O H2CO3 H+ + HCO3 -
CO2 + H2O H2CO3 H+ + HCO3 -
Review of Essential Chemical Reactions
Note: reactions are in equilibrium: the rate of reaction is proceed-ing in the two directions at the same rate.
Below, equilibrium is disturbed. Increased CO2 concentration allows for the production of more H2CO3. The increase in H2CO3 then causes an increase in H+and HCO3 -.
As the reactions proceeds to the right, the concentration of CO2 will go down, until equilibrium is reestablished.
As the reactions proceeds to the left, the concentration of H+ will go down, until equilibrium is reestablished.
Likewise, if the H+ concentration goes up, the reaction will shift to the left, resulting in an increase in H2CO3, and then an increase is CO2 and H2O.
CO2 + H2O H2CO3 H+ + HCO3 -
Page 3
CO
2 +
H
2O
H2C
O3
H
+ +
H
CO
3 -
H+
+
HC
O3
-
H2C
O3
C
O2
+
H2O
CO
2 +
H
2O
H2C
O3
H
+ +
H
CO
3 -
H+
+
HC
O3
-
H2C
O3
C
O2
+
H2O
Body
Cel
lsA
lveo
li of
Lun
gs
Bloo
d
Tran
spor
t
Bloo
d
Tran
spor
t
Inte
rstit
ium
Alv
eoli
In th
e ill
ustra
tion
belo
w, re
actio
ns a
re d
epic
ted
as b
eing
in p
erfe
ct e
quili
briu
m.
Ther
e is
no
met
abol
ism
, the
re is
no
mov
emen
t of g
ases
etc
. Th
is st
ate
does
not
exi
st in
a li
ving
per
son.
Inte
rstit
ium
Alv
eoli
How
ever
, whe
n al
ive,
ther
e is
a “
heal
thy
dise
quili
briu
m”,
whe
re b
ody
cells
pro
duci
ng
CO
2 will
driv
e a
chai
n re
actio
n th
at w
ill le
ad to
the
elim
inat
ion
of C
O2
by th
e lu
ngs.
Page 4
CO2 + H2O H2CO3 H+ + HCO3 -
Body Cells
Interstitium
Page 5
Carbon Dioxide and Acid Production
Buffer System
Note that if interstitial cells produce more CO2, then there will be an increase in H+. The pH is becoming more acid.
The pH of the blood needs to be maintained within a narrow range of the physiological set point of 7.35 - 7.45. Therefore, homeostatic mecha-nisms exist to “buffer against” changes in the acid / base balance. A buffer system is a collection of chemical reactions that can remove H+ and OH- thereby minimizing a disruption of pH. A buffer system can convert a strong acid into a weak acid and a strong base into a weak base. There are many buffer systems in the body. The carbonic acid / bicarbonate buffer system is one of the more important, and uses the chemical reactions and principles covered so far.
By extension, if there is an increase in H+ for a reason other than CO2 production, such as from the diet, the reaction can proceed to the left.
ACID
CO2 + H2O H2CO3 H+ + HCO3 -
ACID
CO
2 +
H
2O
H2C
O3
H
+ +
H
CO
3 -
H+
+
HC
O3
-
H2C
O3
C
O2
+
H2O
Body
Cel
lsD
iet o
r oth
erm
etab
olic
pro
cess
LOW
ERS
pHAC
IDO
SIS
Alv
eoli
of L
ungs
Bloo
d
Tran
spor
t
Inte
rstit
ium
Alv
eoli
If th
ere
is a
n in
crea
se in
aci
d co
ncen
tratio
n, su
ch a
s fro
m th
e di
et o
r som
e ot
her m
etab
olic
pro
cess
, the
n eq
uilib
rium
will
be
furth
er d
istu
rbed
and
the
reac
tion
will
pro
ceed
in a
dire
ctio
n th
at fa
vors
equ
ilibr
ium
. Si
nce
the
cells
of t
he b
ody
will
not
abs
orb
CO
2, th
e re
actio
n w
ill n
ot g
o to
the
left.
Sin
ce C
O2
can
be
elim
inat
e by
the
lung
s, th
e re
actio
n w
ill p
roce
ed to
the
right
. N
ote
that
as t
he C
O2
is e
limin
ated
thro
ugh
the
lung
s, ex
cess
H+
is n
ow in
the
form
of w
ater
, and
has
bee
n re
mov
ed o
ut o
f “ha
rms w
ay”.
We
have
re
stor
ed p
rope
r pH
.
Page 6
Acid
Pro
duct
ion
Rate
of B
lood
Tra
nspo
rtIn
crea
ses
Rate
of V
entil
atio
nin
crea
ses
CO
2 +
H
2O
H2C
O3
H
+ +
H
CO
3 -
H+
+
HC
O3
-
H2C
O3
C
O2
+
H2O
Body
Cel
ls
Die
t or o
ther
met
abol
ic p
roce
ssRA
ISES
pH
ALC
ALO
SIS
Alv
eoli
of L
ungs
Bloo
d
Tran
spor
t
Inte
rstit
ium
Alv
eoli
If th
ere
is a
n in
crea
se is
OH
, th
is w
ill re
act w
ith H
+ an
d pr
oduc
e H
2O.
H+
is st
ill p
rodu
ced
due
to th
e pr
oduc
tion
of C
O2,
but
ther
e w
ill n
ow b
e le
ss n
et H
+ an
d th
eref
ore
the
reac
tion
will
pro
ceed
to th
e rig
ht a
t a
slow
er p
ace,
and
ven
tilat
ion
rate
will
dec
reas
e. W
e w
ill h
ave
rest
ored
pH
.
Page 6
Base
Pro
dcuc
tion
H+
+
OH
-
H
2O
Reca
ll th
at p
ure
wat
er H
2O is
in
per
fect
equ
ilibr
ium
with
H+
and
OH
- .
H2O
OH
-
Rate
of B
lood
Tra
nspo
rtD
ecre
ases
Rate
of V
entil
atio
nde
crea
ses