Moderator : Dr. M. S. SomannavarPresenter : Jay prakash sah

Jawaharlal Nehru Medical college, Belgaum,Karnataka,IndiaEmail:shahjayprakash978@gmail.com

INTRODUCTION

REGULATION OF ACID BASE BALANCE

BLOOD BUFFERS

RESPIRATORY MECHANISM

RENAL MECHANISM

ACID BASE DISORDERS

ABG ANALYSIS

Normal blood PH : 7.35-7.45

Maintenance of blood pH - importanthomeostatic mechanism of the body.

PH less than 7.35 leads to acidosis andpH more than 7.45 leads to alkalosis.

Acids are proton donors.

HA ↔ H+ + A-

HCL ↔ H ++ CL -

Bases are proton acceptors.

NH3+H+ ↔ NH4+

HCO3+H+ ↔ H2CO3

• Weak and strong acids :

HCL → H ++ CL - (COMPLETE) - Strong acid H2CO3 → H+ + HCO3

- ( PARTIAL) - Weak acid

Acid Base

Carbonic acid - Oxidation of c-compounds

Sulphuric acid - Oxidation of sulphur containing amino acids.

Phosphoric acid-metabolism of dietary phosphoproteins ,nucleoproteins, phosphatides .

Organic acid- oxidation of carbohydrates , fats and proteins.e.g. pyruvic acid ,lactic acid , acetoacetic acid etc.

Iatrogenic : - certain medicine like NH4Cl, mandelic acid etc.

NOTE:DIET RICH IN ANIMAL PROTEIN RESULTS IN MOREACID PRODUCTION.

Vegetarian diet has an alkalizing effect.Intestine Blood Cell

From diet

Acid

From foods ,fruits etc

Salts of potasium tartarate + water

Potasium citrate+water

NaHCO3 + H2O

Acetic acid Lactic acid Citric acid Fatty acid

CARBONIC ACID

Lactic acid

Phosphoric acid

Sulphuric acid

TARTARIC ACID+KOH

CITRIC ACID + KOH

CARBONIC Acid+ NaOH

Carbohydrates ,fat, proteins

H2O+ CO2

Glycogen breakdown

NucleoproteinPhosphoproteinPhospholipid metabolism

Cysteine , cystine and methionine metabolism

Buffers - resist change in pH.

Two types

a) Mixture of weak acids with their salt with a strong base.

b) Mixture of weak bases with their salt with a strongacid.

Example1. Bicarbonate buffer (H2CO3 / NaHCO3 )2. Acetate buffer (CH3COOH / CH3COONa)3. Phosphate buffer (Na2HPO4 /NaH2PO4 )

If you go running you build up lactic acid in your muscles.

Therefore your pH will decrease.

Buffer will act to increase the pH.

And vice versa.

So how does it work using chemistry ?

H+ + A- → HA

OH- + HA → A- + H2O

EX;

H+ + HCO3- → H2CO3

OH- + H2CO3 → HCO3- + H2O

Acid add [ H+ ] therefore ↑ [ H+ ] - ↓ pH

Base bind [ H+ ] therefore ↓ [ H+ ] - ↑ pH .

Phosphate buffer

H2PO4 ↔ HPO42- + H+

Protein buffer

Amino acid

If pH ↓

In acidic medium amino acid (NH2) act as a base and absorbs H+.

If pH↑

In alkaline medium amino acid (COOH) act as a acid and release H+.

Acetate buffer

When HCl is added to the acetate buffer, the saltsreact with the acid forming the weak acid , aceticacid and its salts.

CH3COONa + Hcl CH3COOH + Nacl

When NaOH is added, the acid reacts with itsforming salt and water.

CH3COOH + NaoH CH3COONa +Nacl

Thus changes in pH is minimised.

Bicarbonate buffer

H2O + CO2 ↔ H2CO3 ↔ H++ HCO3-

RESPIRATORY RENAL

Le Chatelier’s principle

1. Standard buffer solution are used withindicator for determination of pH.

2. Buffer are used to check the performance ofelectrode used for determination of pH.

3. Used for many chemical reactions includingthose catalysed by enzymes.

4. Used in the pathological laboratory to controlpH of culture media for bacteria tissues.

5. Very important in regulating the pH of bodyfluids e.g. blood, interstitial fluid ,lymph.

Sodium monohydrogen phosphate (Na2HPO4 )

Sodium dihydrogen phosphate ( NaH2PO4 )

Sodium bicarbonate ( NaHCO3 )

Hydrogen carbonate (H2CO3 )

Sodium proteinate

Hydrogen proteinate

.’ ..

erythrocytes

• Potassium bicarbonate

• Carbonic acid

• K2HPO4

• kH2PO4

• Potasium proteinate

• Hydrogen proteinate

Tissue cell

• Potassium proteinate• Hydrogen proteinate• Potasium bicarbonate• Hydrogen bicarbonate• K2HPO4

• kH2PO4

pH = - log [H+] , dimensionless quantity.

[H+] means gm of hydrated H+ ion present asH3O+ per litre of fluid .

E.g. H2O contains 1/1000000gm of hydrogen ionin 1 litre ,means [H+]=10-7.

Decrease of one pH unit represents a ten foldincrease in the H+ activity.

The pH 7.40 corresponds to a hydrogen ionconcentration of 40 nmol/L ( European centre).

Represents the negative logarithm of theionization constant of a weak acid (ka).

Pk is the pH at which an acid is halfdissociated.

Acids have pk value less than 7 and baseshave have more than 7.

Lower pk = stronger acid Higher pk = stronger base

1. Enzyme activity

2. Action potential of myelinated nerve

3. Membrane permeability

4. Control of respiration

5. Heart activity

6. Plain muscle activity

7. Oxygen Hb dissociation curve

8. Nerve excitability

3 mechanism

1. Blood buffers : first line of defence

2. Respiratory regulation :second line of defence

3. Renal regulation : third line of defence

Can not remove H+ ions from the body.

Temporarily acts as a shock absorbant to reduce the free H+ ion.

3 buffer system :

1. Bicarbonate buffer

2. Phosphate buffer

3. Protein buffer

Extracellular buffer system of the body

NaHCO3/H2CO3= [ SALT ] / [ACID]

NORMAL RATIO= 20 : 1

Base constituent (HCO3 ) - regulated by the kidney

(Metabolic component)

Acid (H2CO3) - respiratory regulation ( Respiratory component ).

Neutralization of strong acid and non- volatileacid entering the ECF is achieved by bicarbonatebuffer ,such acid e.g. HCl , H2SO4,lactic acid etc.

Strong acid react with NaHCO3 component .thus lactic acid is buffered as follows:

NaHCO3 H+ L-

Na L-

H2CO3 (weak acid) + Na Lactate (salt)

lungs(H2co3)

HCO3 H+

H2CO3 H+ + HCO3-

By the law of mass action, at equilibrium

Ka = [H+] [HCO3] --------(1)

[H2CO3 ]

[H+] =Ka [H2CO3 ] -------------(2)

HCO3-

By taking reciprocal and logarithm

Log 1/[H+] = log 1/Ka +log [HCO3] --------(3)

[ H2CO3 ]

Ka = dissociation constant

Ka=log 1/[H+]

pH = pka + log [ HCO3 ] -------(4)

[H2CO3 ]

USES;

1. It determines the pH of blood.

2. Serve as an index to understand thedisturbance in acid base balance of thebody.

1. High concentration

2. Alkali reserve

3. Very good physiological buffer and act asfront line of defence.

Na2HPO4 /NaH2PO4

Intracellular buffer , pka= 6.8 , 4:1.

When a strong acid enters ,it is fixed up by thealkaline po4(Na2hpo4) which is converted to acid po4as follows

Hcl Na2HPO4

Cl- Na+

NaH2PO4 +NaClexcreted through urine(kidney)

H+ NaHPO4

When a alkali enters , buffered by acid PO4, which is converted to alkaline PO4 and is excreted in urine.

NaH2PO4 NaOH

NaHPO4 Na+

H2O+Na2HPO4

excreted in urine

H+ OH-

Advantage

Very effective and better, as pka approaches physiological ph.

Plasma Protein and Hb - most important

Buffering action of protein depends on pk of ionizable group of amino acid

Effective group- imidazole group of Histidine

Pk - 6.7

In acidic medium, protein acts as a base, NH2

group takes up H+ ions from the mediumforming NH3+, proteins becomes positivelycharged.

in alkaline medium , protein act as an acid,

COOH group dissociates and gives H+,forming COO-. H + combines with OH- toproduce molecule of water , proteins becomenegatively charged

The respiratory system helps control theacidity of the blood by regulating theelimination of CO2 and H2O.

These molecules are exhaled with everybreath.

H2CO3 H2O + CO2

carbonic acid

The brain is sensitive to blood CO2 levels andpH.

→ Normal blood

pH

→

↑ ↓

Lower blood pH,

higher CO2 levels

↑ ↓

Decreased blood CO2,

increased blood pH

Respiratory

center

stimulated

↑ ↓

Faster, deeper

breathing

↑ ↓

← Increased

amount

of CO2 exhaled

←

A significant decrease in CO2 or increase in pH- causes breathing to decrease- results in hypoventilation- less CO2 is exhaled- increases CO2 - increases H2CO3 and H+ concentrations

- decreases pH back to normal

→→ Normal blood

pH

→→

↑ ↓

Higher blood pH,

lower CO2 levels

↑ ↓

Increased blood CO2,

decreased blood pH

Respiratory

center

stimulated

↑ ↓

Slower, shallower

breathing

↑ ↓

← Decreased

amount

of CO2 exhaled

←

• Third line of defense against change inhydrogen ion concentration

• permanent solution to the acid basedisturbances.

• Kidneys require hours to days tocompensate for changes in body-fluid pH

1. Excretion of H+.

2. Reabsorption of bicarbonate

3. Excretion of titratable acid

4. Excretion of ammonium (NH4+)

Plasma PCT CELL Tubular lumen

Na+

HCO3-

( alkali is recovered )

Na+

HCO3- + H+

H2CO3

CA

CO2 + H2O

Na+

H+

Excreted in urine

plasma PCT cell Tubular lumen

Na+

HCO3-

Na+

HCO3- + H+

H2CO3

CA

CO2 + H2O

NaHCO3 (filtered)

Na+ HCO3-

H+

H2CO3

CA

CO2 + H2O

plasma DCT cell tubular lumen

Na+

HCO3-

Na+

HCO3- + H+

H2CO3

CA

CO2 + H2O

Na2HPO4 (ph-7.4)

Na+

H+

NaH2PO4 (ph-5.4)

Excreted in urine

Plasma DCT cell tubular lumen

Na+

HCO3-

+H2OGlutamine glutamate

glutaminaseNH3

Na+

HCO3- + H+

H2CO3

CA

CO2 + H2O

NH3

Na+

H+

NH4+( H+ trapped and excreted)

A 50 year old man came to emergency department after returningfrom foreign travel. His symptom included persistent diarrhoea (overthe past 3 days) and rapid respiration . Blood gases were drawn withfollowing results :

pH- 7.21 ( )

pCO2 - 19 mmHg ( )

pO2 - 96 mmHg

HCO3- 7 mmol/l

Questions:

1. What is the patient acid base status?

2. Why is the HCO3 level is so low?

3. Why does the patient have rapid respiation?

ACIDOSIS: PH <7.35

a ) METABOLIC ACIDOSIS

b ) RESPIRATORY ACIDOSIS

ALKALOSIS : PH >7.45

a ) METABOLIC ALKALOSIS

b ) RESPIRATORY ALKALOSIS

The sum of cations and anions in ECF isalways equal , so as to maintain the electricalneutrality.

Commonly measured electrolytes in plasmaare Na+, K+,Cl-,HCO3- .

Unmeasured anion in the plasma constitutesthe anion gap.

This is due to presence of protein anions ,sulphate , phosphate and organic acids.

Anion gap = (Na + k) - ( HCO3+ Cl- ) .

Normally anion gap is about 15 mEq/l

Normal range = 8-18 mEq/l.

High anion gap acidosisI. Renal failureII. Diabetic ketoacidosisIII. Lactic acidosis

Normal anion gap acidosisI. DiarrhoeaII. Hyperchloremic acidosis

Low anion gapI. Multiple myeloma

Primary deficit of bicarbonate.

Due to its utilization in buffering H+ ions,loss in urine or GIT .

Important cause-excessive production oforganic acids which combine with sodiumbicarbonate and deplete alkali reserve .

NaHCO3+organic acids Na salts of o organic acids + CO2

Severe uncontrolled diabetes mellitus(ketoacidosis)- production of organic acids

Renal failure

Lactic acidosis

Severe diarrhoea

Renal tubular acidosis

Increased production and accumulation of organic acid causes an elevation in anion gap.

This type is seen in ketoacidosis

COMPENSATION• Hyperventilation of lungs(elimination of co2)

• Renal compensation-(3-4days) H+ ions excreted as NH4+

Primary excess of carbonic acid .

Causes

• Severe asthma

• Pneumonia

• Cardiac arrest

• Depression of respiratory centre

• COPD

Compensation

H2O + CO2 ↔ H2CO3 ↔ H++ HCO3-

renal mechanism-

• Increase in renal reabsorption of bicarbonate

• excretion of titrable acidity and NH4+ iselevated in urine

Primary excess of bicarbonate

Causes• Severe vomiting

• Hypokalemia

• Intravenous administration of bicarbonate.

• Cushing syndrome

M. alkalosis is commonly associated withhypokalemia .

In severe k+ deficiency ,H+ ions are retainedinside the cells to replace missing k+ ions.

In the tubular cells, H+ions are exchanged(instead of k+) with the reabsorbed Na+.

Paradoxically , the patient excretes acid urinedespite alkalosis.

COMPENSATION

H2O + CO2 ↔ H2CO3 ↔ H++ HCO3-

HYPOVENTILATION- to retain co2

Renal mechanism-

excretes more bicarbonate and retains H+

Primary deficit of carbonic acid

causes

• Hyperventilation

• High altitude

• Salicylate poisoning

Compensation

H2O + CO2 ↔ H2CO3 ↔ H++ HCO3-

Renal mechanism –

by increasing excretion of bicarbonate by decreasing reabsorption

secretion of H+ decreases

Potassium- affects contractility of heart

Hypokalaemia - life threatening

Insulin – increases K+ uptake by cells

Measurement of plasma k+ concentration

assumes significance in acid-base disorders.

Patients with severe uncontrolled DM (M.acidosis) is usually with hypokalemia.

When such a patient is given insulin , itstimulates k+ entry into cells.

The result is that plasma k+ level is furtherdepleted.

Hypokalemia affects the heart functioningand is life threatening.

Therefore in the treatment of diabetic ketoacidosis,

k+ has to be given.

K+ and alkalosis

Hypokalemia leads to increased excretion of hydrogen

ions, and thus may cause M. alkalosis.

Assessment of acid base status.

Arterial blood

Radial artery – in the Wrist

Brachial artery - in the arm

Femoral artery - in the groin

parameter value

[H+] 35-43 mmol/l

pH 7.35-7.45

pco2 4.5-6.0 kpa34-45 mmHg1.02-1.35 mmol/l

po2 10.5-13.5 kpa

Bicarbonate 24-30 mmol/l

pH co2 Hco3- H+

Respiratory acidosis ⇩ ⇧* ⇧ ⇧

Respiratory alkalosis ⇧ ⇩* ⇩ ⇩

Metabolic acidosis ⇩ ⇩ ⇩* ⇩

Metabolic alkalosis ⇧ ⇧ ⇧* ⇩

Co2+H20 ↔ H2CO3 ↔ H+ +HCO3-

A) Arterial blood gas analysis

PH- 7.31 ( ↓) ,

Pco2-55 mmHg (↑) ,

HCO3-28 mmol/l (Normal)

respiratory acidosis w/o compensation.

B)ABG

Ph-7.31

Pco2-55mmhg

Hco3-35mmol/l (abnormal)

Respiratory acidosis with compensation

TIETZ TEXT BOOK OF CLINICAL CHEMISTRY

VARLEY’S CLINICAL CHEMISTRY

MICHAEL L. BISHOP, CLINICAL CHEMISRY ,SEVENTH EDITION.

DM VASUDEVAN TEXTBOOK OF BIOCHEMISTRY

U. SATYANARAYANA TEXTBOOK OF BIOCHEMISTRY

LAWERENCE A. KAPLAN A TEXT BOOK OF CLINICAL CHEMISTRY

DR. R. N. ROY A TEXT BOOK OF BIOPHYSICS