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Concept of pH and

buer

Dr. Zakiah Jubri

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Objectives

At the end of the lecture, studentsshould be able to:

describe the concept of ionization, p andp!a

de"ne acids, bases and their relation innor#al #etabolis#.

e$plain the enderson%asselbalche&uation.

e$plain the principle of bu'er and itsfunction in hu#an bod(

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)eferences

*rinciples of +ioche#istr(. orton )., oran -A.,Ochs )., )a/n JD., cri#0eour !1. 2332.4hird5dition. *rentice%all, 6nc, 7J.

edical +ioche#istr(. +ha0avan 78. 9ourth 5dition.2332. arcourt Acade#ic *ress, an Die0o. arpers 6llustrated +ioche#istr(. urra( )!.,

1ranner D!., a(es *A., )od/ell 8;. 4/ent( si$thedition. 233ra/%ill, 7?.

+asic edical +ioche#istr(. A clinical approach.arks D+., arks AD., #ith >. @B. -ippincott;illia#s C ;ilkins.

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;ater

*ure /ater consists of 2O. ;ater #olecule can dissociate and ionize to

for# h(dro0en ions, Dand h(dro$(l ions, O%.

4hese 2 products inEuences cells constituents[D]deter#ines p of the #ediu# 6nEuences catal(tic activities of various cellular

enz(#es

H2O H+ + OH-

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9or# h(dro0enbonds bet/een

positive pole andne0ative pole of/ater #olecule.

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olvent *roperties

+ecause of its dipolar character

6n the cr(stal structure, 7a>l is held to0ether b( stron0electrostatic attractions bet/een 7aand >l%

6n /ater, ne0ative pole of the /ater is attracted to/ards 7a

and positive pole to/ards >l%

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6n the hu#an bod( contains inor0anic cations and anions.

>ations are attracted to the o$(0enato# and anions h(dro0en ato#s.

6on%dipole interactions hold the co#ponents of soluble salts insolutions.

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p

easure the proton []concentration in #oles per liter. De"nes as ne0ative lo0arith# of h(dro0en ion

concentration, e$pressed in #olesp F % lo0 []

4he nor#al p of hu#an blood %ph(siolo0ical p is G.l fro# the sto#ach h(perventilation Ie$cessive loss of carbonic acid as

carbon dio$ide.

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Acids % referred as proton donors +ases %proton acceptors

tron0 acids and stron0 bases dissociate co#pletel( in /ater, such as >l and7aO.

;eak acids and /eak bases. do not dissociate co#pletel( in /ater.

such as the a#ino acids Iproteins purines and p(ri#idines ID7A and )7A 6#portant in livin0 s(ste#s

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)elationshipbet/een acidsand bases

>l 2O >l% l conju0ateacid of 2O

;eak acids

>OO

>OO%

Acetic acidI/eak acid

Acetate anionIconju0ate base

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Dissociation constant IKa

9or a /eak acid indicates the tendenc( of the acidto lose its proton and for# its conju0ate baseA A%

Ka F [

][A%

] [A]

9or acetic acid.Ka

F [

][>OO%

] [>OO]

Ka F @.GB K @3%L at 2Lo>

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Henderson-HasselbalchEquation

pF pKa lo0 [conju0ate base] [/eak acid]

pKavalue is a #easure of the acid stren0th of aparticular co#pound. pKaF2 M LpFpKa, a /eak acid is L3N dissociates

pF pKa lo0 [A%] [A]

pF pKa lo0 [*roton acceptor] [*roton donor]

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+995)

6s a s(ste# that resists an( chan0es in its p/hen a s#all a#ount of acid or alkali is added.

>onsists of a /eak acid and its conju0ate base.

5'ectiveness of a bu'er4hese t/o co#ponents are present in e&ui#olar

concentrations p Iof the #ediu# e&uals to p!a Iof the acid%base

pair

6t re#ains e'ective bet/een @ p unit belo/and @ unit above the pKa

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p L.GB IZoneof bu'erin0capacit(

p

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+od( Euids #ust be protected a0ainstchan0es in p because #ost enz(#es arever( p sensitive.

>onstantl( active because #etabolis#involves the production of acids and bases.

-on0 ter#, e$cess acid or base is

eli#inated via the kidne( and the lun0s hort ter#, b( bu'erin0 s(ste#

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p of the blood is #aintained G.

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+icarbonate +u'er (ste#

>arbonic acid andbicarbonate

6s re0ulated b(kidne( and lun0s.

>O2 #ajor source of

#etabolic acid inthe bod(

produced fro# fuelo$idation in the

4>A c(cle

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>O2Id in bloodF >O2I0 in lun0 [2>OO2I0

[

]increases, it /ill be taken up b( >O%

OO2Id in the bloodincreases increase in the pressure of >O2 inthe lun0s and e$haled throu0h increased rateof breathin0.

[]reduces, rate of breathin0 reduces, >O2retained, for# >O2Id , for# 2>O< , back tonor#al.

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+icarbonate and

e#o0lobin +u'erin0 the blood and transportin0 >O2to the lun0.

>O2di'uses interstitial Euid blood

plas#a )+> Icarbonic anh(drase

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*hosphate anions and

proteins aintainin0 a constant

p of intracellularEuids.

*hosphate anions 6nt bu'er in )+> and cells >onc is #uch hi0her than

in blood and interstitialEuid

Or0anic phosphateanions 1lucose B%phosphate and

A4*

*rotein% histidine anda#ino acids Accept

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Acetoacetic acid and %h(dro$(but(ric acid 9ro# fatt( acid o$idation to ketone bodies

-actic acid 1l(col(sis >ell beco#es too acidic,

#ore is transported out in e$chan0e for 7aions

>ell beco#es too alkaline, #ore bicarbonate is transported out in e$chan0e for >l%ions.

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4A7! ?O