ACID BASE BALANCE
and Disorders
Acids :
Are any substance which tends to release H+ in
water , either by simple dissociation or reaction
 The strength of acids is measured by the extent
to which it liberate H+ but not by the number of
H+ in the acid molecule e.g. phosph . a. and
carbonic a . are weaker than HCL ( the later is
completely dissociated ).
 The acidity of the solution is determined by
H- expressed in gm ion/l. ( or nmol/l.).

Bases:
 Are
substances which tends to accept H+,
since the anion liberated along with H+
when acid dissociated were bases e.g. Cl
in HCL, NH3 in NH+4
 The strong base is that substance with
high tendency to accept H+ e.g. anion of
weakly dissociated acid e.g H2CO3
Aprote:
 Metallic
cation e.g Na+ , K+
which are not bases or acids
HYDROGEION HOMEOSTASIS
The buffer :
 It
is the substance which resists
change in its PH, when excess acid or
base is added
 Usually
are weak acids and its salts
e.g. H2CO3
 Addition
of acids → dissociation of
the weak acid or its salt e.g. H2CO3 (
H+ , HCO3 0 slowely and the anion
neutralize any excess acid ( H+) e.g
HCL +NaHCO3 → NACl + H2CO3. (
weak acid is formed instead of strong
one ).
 Addition
of bases → dissociation of
the weak acid H + +HCO3 , H+
neutralize the base added without
great change in PH.
→pH←

It is log10
1
H+
Log10 of the
reciprocal of (H+)

The Log10 of a number is the power to which 10
must be raised to produce this number e.g log10
102 = if log10 to "x" number = 7 so the number
must be 107

At pH6 (H+) =??
pH = Log10
1
H+
Log10 (H+) = 6
( H+) 10-6 = 0.000001 mol = 1000nmol/L
at pH7 , (H+) will be 100 nmol/L so
each one unit change in pH mean 10
folds change in (H+)
Blood Buffer systems
1)
Bicarbonate / Carbonic acid

The most important buffer of
plasma

It presents in RBCs , but in lesser
concentration
HANDERSON – HASSELBALCH
equation
CO2 + H2O
hydration
H2CO3
H++ HCO3
K hydration =
H2CO3 →
H2CO3
CO2xH2O
H+ + HCO3
dissoeiation
H+ x HCO3
K dissociation =
H2CO3
H2CO3
K combined = CO2xH2O x
H+ xHCO3
H2CO3
H+ x HCO3
CO2xH2O
H2O is constant and so K → K`
=
K` =
H+ x HCO`3
dCO2
( H+) = K` x
pH = Log10
= pK + Log
dCO2
HCO`3
1
(H+)
= Log
HCO`3
0.03xPCO2
1
K
+ log
HCO`3
dCO2
Note:
( dissociation constant of CO2 =
0.03)
( PK. For BiC. / Carb. Buffer
system = 6.1)
2) Phosphate buffer : Inorganic
phosphate accounts for 5% of
the nonbicarbonate buffer value, at a
plasma Ph of 7.4 , the ratio HPO4/H2PO4
is 80/20 ( 4/1) (PK=6.8)
 Organic
phosphate in the RBCs in the
form pf 2.3-diphosphoglycerate
accounts for 16% of the non
bicarbonate buffer.
H2PO4+OH= HPO`4 + H2O
HpO`4 + H= = H2Po4
3) Plasma protein buffer: Albumin
form 95% of the non
bicarbonate buffer value of the
plasma
 The
most important buffer groups of
proteins are the imidazole group of
histidine ( 16 in each albumin
molecule)
Hemoglobin buffer :
 Account
for 84% of the RBCs non
bic buffer the most important
buffer groups are imidazole
groups of Hb. Histidine
Carbamino Compoands :
Combination of small amount of CO2 in
RBCs with Hb.R – NH2 + Co2 R – NH –
COO + H+
Regulation of (H+)
1.
2.
a.
b.
c.
Dilution
Buffer system
→
Plasma
HCO3/H2CO3 (20:1)
B2HPO4 / BH2PO4 ( 4:1)
Prot. /prot.H(95% of the non bic
RBCs :
HbO2 / HHb ( 84% of the non bicarb.)
b) Carbamino compounds
c) HCO3 /H2CO3 ( to less extent)
d) 2.3 diph. glye.16%of the non bic.
a)
3 . Respiratory Mechanism = C.R.C. (
Central chem.., Periph. Chem.)
4 . Renal Mechanism
a) Acid excrction
b) Na+ -H+ exchange
c) Ammonia formation and NH+4 excretion
d) H2PO4 excretion
e) HCO`3 reclamation