PH REGULATION AND ACID BASE BALANCE

DR SAKINA ,MBBS,M.D SENIOR LECTURER ,MSU

OUT LINE

Introduction to Acid base balance Review- Importance of Ph Buffer System Respiratory regulation of Ph Acidosis and Alkalosis Blood gas analysis

2

PH REVIEW

pH• p

stands for power and

• H for hydrogen ion conc.

If [H+

] is high

• the solution is acidic; pH < 7

If [H+

] is Low

• the solution is basic or alkaline pH > 7

Basic

pH neutral

Acidic

Death

Normal and abnormalpH ranges of blood

pH’s of commonsubstances

Death

Acidosis

Normal

Alkalosis

8.00

7.45

7.35

6.8

Battery acid

Concentrated lye

Water

Gastric juiceLemon juiceVinegar

Household ammonia

Baking soda

Pancreatic juiceBlood

MilkUrine

Coffee

Orange juice

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

SOURCE OF H+

1. •Anaerobic respiration of glucose produces lactic acid.

2.• Breakdown of phosphorus-

containing proteins releases phosphoric acid

3. • Cellular metabolism produces CO2.

4. • Fat metabolism yields organic acids and keto acids

SOURCE OF H+

Volatile acid

Carbonic acid(H2CO3)CO2

Non volatie(Fixed acid)

Lactic acid, keto acids, sulfuric acid andphosphoric acid.

1. volatile acids (The carbonic acid) is eliminated as CO2 by the lungs.

2.The fixed acids(non-volatile) are buffered and later the H+ are excreted by the kidney.

lactate and keto acids are produced in relatively fixed amounts. e.g. 1 mol of glucose produces 2 mols of lactic acid. sulfoproteins yield sulfuric acid and phosphoproteins and nucleoproteins yield phosphoric acid. On an average 3 g each of phosphoric & sulfuric acid are

produced/day

SMALL CHANGES IN PH CAN PRODUCE MAJOR DISTURBANCES

Most enzymes function only with narrow pH ranges Can also affect hormones

MECHANISM OF REGULATION OF PH

First line of defence

•Blood Buffer

Second line of Defence

•Respiratory Regulation

Third line of Defence

•Renal Regulation

BUFFER SYSTEM

•A chemical substance that minimizes changes in pH by releasing or binding hydrogen ions1•Most buffers composed of weak acid and weak base2•The purpose of the buffer is to help the body maintain pH3

Buffer Systems

Extracellular fluid (ECF)

Bicarbonate BufferSystem

Protein Buffer Systems

Protein buffer systems contribute to the regulationof pH in the ECF and ICF. These buffer systems interactextensively with the other two buffer systems.

Hemoglobin buffersystem (RBCs only)

Amino acid buffers(All proteins)

Plasma proteinbuffers

Phosphate BufferSystem

intracellular fluid (ICF)

occur in

The carbonic acid–bicarbonate buffersystem is mostimportant in the ECF.

The phosphatebuffer systemhas an importantrole in bufferingthe pH of the ICFand of urine.

BICARBONATE BUFFERING SYSTEM Most important buffer system It accounts for 65% of buffering capacity in plasma The base, bicarbonate (HCO3–),is regulated by the

kidney (metabolic component). Acid part, carbonic acid (H2CO3), is under respiratory

regulation (respiratory component). The normal bicarbonate level of plasma is 24

mmol/liter The normal carbonic acid concentration in

blood is 1.2 mmol/L.

BICARBONATE BUFFERING SYSTEM• It tends to maintain a relatively constant plasma pH and counteract any force that would alter

• In this  (CO2) combines with (H2O) to form (H2CO3), which rapidly dissociates to form hydrogen ions (H+) and bicarbonate (HCO3- )

THE CARBONIC ACID-BICARBONATE BUFFER SYSTEM

LIMITATIONS OF CARBONIC ACID–BICARBONATE BUFFER SYSTEM

. •Ability to buffer acids is limited by availability of bicarbonate ions

. •Functions only when respiratory system and respiratory control centers are working normally

PHOSPHATE BUFFERNaH2PO4- Na2HPO4 constitute

the phosphate

buffer.

It is mostly an

intracellular buffer and is

of less importance in plasma due to its

low concentratio

n.

Phosphates are major

anions in ICF and minor

ones in ECF

PROTEIN BUFFER

It is account for about 2% of the total buffering capacity

The plasma proteins and hemoglobin together constitute the protein buffer system

Carboxyl group gives up H+ Amino Group accepts H+

PROTEIN BUFFER Buffering capacity of protein depends on the pKa

value of ionizable side chains. The most effective group is Histidine imidazole

group with a pKa value of 6.1. The role of the hemoglobin buffer is considered along

with the respiratory regulation of pH.

ACTION OF HAEMOGLOBIN

1• Transport CO2 formed in

tissue with minimal change in pH

2• It serves to generate

bicarbonate by activity of carbonic unhydrase system

3• The reverse occurs in lungs

during oxygenation and elimination of CO2

GENERATION OF BICARBONATE BY ERYTHROCYTES

Step -1•Plasma co2 diffuses into RBC ,combines with H2O to form H2CO3•In the RBC, H2CO3 dissociates to produce H+ and HCO3

Step -2•The H+ ions are trapped and buffered by hemoglobin. As the concentration of HCO3 increases in the RBC, it diffuses into plasma along with the concentration gradient, in exchange for Cl- ions, to maintain electrical neutrality

CHLORIDE SHIFT

RESPIRATORY REGULATION OF PH•Achieved by Regulating the concentration of H2CO3 in blood. CO2 diffuses from cells into ECF & Reaches lungs through blood

•The rate of respiration is controlled by chemoreceptors in respiratory centre

•Fall in pH (acidosis) the respiratory rate is stimulated in hyperventilation to eliminate more CO2 ,thus lowering H2CO3

But This cannot continue for long

RATES OF CORRECTION

Buffers function almost instantaneously

Respiratory mechanisms take

several minutes to hours

Renal mechanisms may take several hours to

days

BLOOD GAS ANALYSIS

1 •1.To Determine if the patient is well oxygenated

2 •2.To Determine the patient’s Acid Base balance

Blood Gas are obtained for two reasons

Test are measured using arterial blood and procedure is known as “ABG”Arterial blood gas by (ABG Analyser).

MEASUREMENT – BLOOD GASES

pH, pCO2, pO2 – Measured directlyHCO3

-, O2 saturation (usually) – Calculated from pH, pCO2, and pO2

Arterial Venous

pH 7.35-7.45 7.32-7.42

PO2 80-100 mmHg 28-48 mmHg

PCO2 35-45 mmHg 38-52 mmHg

HCO3- 22-26 mEq/l 19-25 mEq/l

SOME NORMAL PARAMETERS

F THE BASIC RELATIONSHIP BETWEEN PCO2 AND PLASMA PH

PCO2

40–45mm Hg HOMEOSTASIS

If PCO2 rises

When carbon dioxide levels rise, more carbonic acidforms, additional hydrogen ions and bicarbonate ionsare released, and the pH goes down.

PCO2

pH

H2O CO2 H2CO3 HCO3H

THE BASIC RELATIONSHIP BETWEEN PCO2 AND PLASMA PH

pH

PCO2

When the PCO2 falls, the reaction runs in reverse, andcarbonic acid dissociates into carbon dioxide and water.This removes H ions from solution and increases thepH.

pH7.35–7.45HOMEOSTASIS

If PCO2 falls

H HCO3 H2CO3 H2O CO2

RESPIRATORY ACIDOSIS/ALKALOSIS

RESPIRATORY ACIDOSIS

Primary changes

RESPIRATORY ALKAOSIS

Primary changes

ACID BASE IMBALANCE

SOME IMPORTANT CAUSES OF

RESPIRATORY ACIDOSIS RESPIRATORY ALKALOSIS

•Respiratory depression1•Obstructed airway2•Chest wall injury•Pulmonary edema3

• Anaemia1• High altitude 2• Sepsis ,Shock,• other Respiratory

ailments3

THANK YOU