a buffer system - noel waysnoelways.com/courses/anatomy and physiology i...buffer system is a...

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





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.


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.


Body Cells

Interstitium

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


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

.

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

a buffer system - noel waysnoelways.com/courses/anatomy and physiology i...buffer system is a...

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