ACID BASE BALANCE ACID BASE BALANCE and Disordersand Disorders

AcidsAcids: :

Are any substance which tends to release Are any substance which tends to release H+ in water , either by simple dissociation H+ in water , either by simple dissociation or reactionor reaction

The strength of acids is measured by the The strength of acids is measured by the extent to which it liberate H+ but not by extent to which it liberate H+ but not by the number of H+ in the acid molecule the number of H+ in the acid molecule e.g. phosph . a. and carbonic a . are e.g. phosph . a. and carbonic a . are weaker than HCL ( the later is completely weaker than HCL ( the later is completely dissociated ).dissociated ).

The acidity of the solution is determined The acidity of the solution is determined by H‑ expressed in gm ion/l. ( or nmol/l.).by H‑ expressed in gm ion/l. ( or nmol/l.).

BasesBases::

Are substances which tends to Are substances which tends to accept H+, since the anion liberated accept H+, since the anion liberated along with H+ when acid dissociated along with H+ when acid dissociated were bases e.g. Cl in HCL, NH3 in were bases e.g. Cl in HCL, NH3 in NH+4NH+4

The strong base is that substance The strong base is that substance with high tendency to accept H+ e.g. with high tendency to accept H+ e.g. anion of weakly dissociated acid e.g anion of weakly dissociated acid e.g H2CO3H2CO3

AproteAprote::

Metallic cation e.g NaMetallic cation e.g Na++ , K , K++ which are not bases or which are not bases or acidsacids

HYDROGEION HYDROGEION HOMEOSTASISHOMEOSTASIS

The buffer :The buffer :

It is the substance which resists It is the substance which resists change in its PH, when excess change in its PH, when excess acid or base is addedacid or base is added

Usually are weak acids and its Usually are weak acids and its salts e.g. H2CO3 salts e.g. H2CO3

Addition of acids → dissociation Addition of acids → dissociation of the weak acid or its salt e.g. of the weak acid or its salt e.g. H2CO3 ( H+ , HCO3 0 slowely and H2CO3 ( H+ , HCO3 0 slowely and the anion neutralize any excess the anion neutralize any excess acid ( H+) e.g HCL +NaHCO3 → acid ( H+) e.g HCL +NaHCO3 → NACl + H2CO3. ( weak acid is NACl + H2CO3. ( weak acid is formed instead of strong one ).formed instead of strong one ).

Addition of bases → dissociation Addition of bases → dissociation of the weak acid Hof the weak acid H+ + + + HCO3 , H+ HCO3 , H+ neutralize the base added without neutralize the base added without great change in PHgreat change in PH..

→→pHpH←←

It is logIt is log1010 Log Log1010 of the of the reciprocal of (H+)reciprocal of (H+)

The Log10 of a number is the power to The Log10 of a number is the power to which 10 must be raised to produce this which 10 must be raised to produce this number e.g log10 102 = if log10 to "x" number e.g log10 102 = if log10 to "x" number = 7 so the number must be 107number = 7 so the number must be 107

At pH6 (H+) =??At pH6 (H+) =??

1

H+

pH = LogpH = Log1010 Log Log1010 (H+) = 6 (H+) = 6

( H+) 10-6 = 0.000001 mol = ( H+) 10-6 = 0.000001 mol = 1000nmol/L1000nmol/L

at pH7 , (H+) will be 100 nmol/L so at pH7 , (H+) will be 100 nmol/L so each one unit change in pH each one unit change in pH mean 10 folds change in (H+)mean 10 folds change in (H+)

1 H+

Blood Buffer systemsBlood Buffer systems

1)1) Bicarbonate / Carbonic acidBicarbonate / Carbonic acid

The most important buffer of The most important buffer of plasmaplasma

It presents in RBCs , but in It presents in RBCs , but in lesser concentrationlesser concentration

HANDERSON HANDERSON –– HASSELBALCH HASSELBALCH equationequation

COCO22 + H + H22O HO H22COCO33

HH+++ HCO+ HCO33

K hydration = K hydration =

HH22COCO33 → H → H++ + HCO + HCO33

H2CO3 CO2xH2O

hydration dissoeiation

K dissociation = K dissociation =

K combined = x K combined = x ==

HH22O is constant and so K → K`O is constant and so K → K`

H+ x HCO3

H2CO3

H2CO3

CO2xH2OH+ xHCO3

H2CO3

H+ x HCO3

CO2xH2O

K` =K` =

( H+) = K` x( H+) = K` x

pH = LogpH = Log1010 = Log + log = Log + log

= pK + Log = pK + Log

H+ x HCO`3

dCO2

dCO2

HCO`3

1

(H)+

1

K

HCO`3

dCO2

HCO`3

0.03xPCO2

( dissociation constant of CO2 ( dissociation constant of CO2 = 0.03)= 0.03)

( PK. For BiC. / Carb. Buffer ( PK. For BiC. / Carb. Buffer system = 6.1)system = 6.1)

NoteNote : :

Inorganic phosphate accounts for 5% Inorganic phosphate accounts for 5% of the nonbicarbonate buffer value, of the nonbicarbonate buffer value, at a plasma Ph of 7.4 , the ratio at a plasma Ph of 7.4 , the ratio HPO4/H2PO4 is 80/20 ( 4/1) (PK=6.8)HPO4/H2PO4 is 80/20 ( 4/1) (PK=6.8)

22 ) )Phosphate bufferPhosphate buffer-: -:

Organic phosphate in the RBCs in Organic phosphate in the RBCs in the form pf 2.3-the form pf 2.3-diphosphoglycerate accounts for diphosphoglycerate accounts for 16% of the non bicarbonate 16% of the non bicarbonate buffer.buffer.

H2PO4+OH= HPO`4 + H2OH2PO4+OH= HPO`4 + H2O

HpO`4 + H= = H2Po4HpO`4 + H= = H2Po4

Albumin form 95% of the non Albumin form 95% of the non bicarbonate buffer value of the bicarbonate buffer value of the plasmaplasma

The most important buffer The most important buffer groups of proteins are the groups of proteins are the imidazole group of histidine ( 16 imidazole group of histidine ( 16 in each albumin molecule)in each albumin molecule)

Plasma protein buffer:-Plasma protein buffer:- 33))

Account for 84% of the RBCs Account for 84% of the RBCs non bic buffer the most non bic buffer the most important buffer groups are important buffer groups are imidazole groups of Hb. imidazole groups of Hb. HistidineHistidine

Hemoglobin buffer:

Carbamino Compoands :Carbamino Compoands :

Combination of small amount of Combination of small amount of

COCO22 in RBCs with Hb.R in RBCs with Hb.R –– NH NH22 + +

CoCo2 2 R R –– NH NH –– COO + H+ COO + H+

1.1. DilutionDilution

2.2. Buffer system → PlasmaBuffer system → Plasma

a.a. HCO3/H2CO3 (20:1)HCO3/H2CO3 (20:1)

b.b. B2HPO4 / BH2PO4 ( 4:1)B2HPO4 / BH2PO4 ( 4:1)

c.c. Prot. /prot.H(95% of the non bic Prot. /prot.H(95% of the non bic

Regulation of (H+)

RBCs :RBCs :

a)a) HbO2 / HHb ( 84% of the non bicarb.)HbO2 / HHb ( 84% of the non bicarb.)

b)b) Carbamino compoundsCarbamino compounds

c)c) HCO3 /H2CO3 ( to less extent)HCO3 /H2CO3 ( to less extent)

d)d) 2.3 diph. glye.16%of the non bic.2.3 diph. glye.16%of the non bic.

3 . Respiratory Mechanism3 . Respiratory Mechanism = C.R.C. ( = C.R.C. ( Central chem.., Periph. Chem.)Central chem.., Periph. Chem.)

4 . Renal Mechanism4 . Renal Mechanism

a)a) Acid excrctionAcid excrction

b)b) Na+ -H+ exchangeNa+ -H+ exchange

c)c) Ammonia formation and NH+4 Ammonia formation and NH+4 excretionexcretion

d)d) H2PO4 excretionH2PO4 excretion

e)e) HCO`3 reclamation HCO`3 reclamation