Acid Base Bal Rsl

8/3/2019 Acid Base Bal Rsl

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ACID BASE BALANCE

pH (Potential of Hydrogen) =Log H+

The concept was introduced byS.P.L.S. Rensen in 1909

Acid - Release H + ions

Base - Accept H+

ions



2

Buffer system

Provide or remove H+ and stabilize the pH

Include weak acids that can donate H+

andweak bases that can absorb H+

Does NOT prevent a pH change



3

pH different in different fluids

Blood pH 7.4

Urine 4.5 8.0 Gastric HCl 0.8



4

What happens if body is too acidic

q Energy Production

q Ability to repair damaged cells

q ability to detoxify heavy metals

Enable tumor cell to thrive

Susceptible to illnessTherefore Acidosis is more dangerous



5



6

Body produces more acids

than bases Acids taken in the foods

Acids produced by metabolism of lipids& Proteins

Cellular metabolism produces CO2

CO2+H2O H2CO3 H

+

+ HCO3

-



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First line of Defence

Second line of Defence

Chemical

Buffer

Physiological

Buffer

Bicarbonate

Buffer system

Phosphate

Buffer system

ProteinBuffer system

Respiratory

Mechanism

(CO2 Excretion)

Renal

Mechanism

(H+ Excretion)



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Defense against H+ concentration

Chemical buffer system

Within fraction of a second Bicarbonate Buffer system

Phosphate Buffer system

Protein Buffer system

Haemoglobin Respiratory system - Within few minutes

Renal system - Slowly but very powerful



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Bicarbonate Buffer system Present in large quantities

Respiratory and renal systems act onthis buffer system

Most important ECF buffer



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Bicarbonate BufferNaHCO3 and H2CO3

20:1 ratio , HCO3- : CO

2

HCl + NaHCO3 H2CO3+NaCl

NaOH + H2CO3 NaHCO3 + H2O

Henderson Hesslebach EquationpH=pk +log Base

acid



11

Phosphate Buffer system Low activity in ECF

Better buffer in the ICF, Kidneys andbone

pK = 6.8

HPO4

2-

& H2PO4

-

H+ + HPO42- H2PO4

-

OH- + H2PO4- H2O + HPO4

2-



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Proteins Buffer system Abundant in Blood and ISF pK close to 7.4 Carboxyl group gives up H+

Amino group Accepts H+

RCOOH RCOO- + H+

RNH3 + H+ RNH4+

Haemoglobin Buffer Inside RBCs, Less efficient pK = 7.7



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Respiratory system 2nd line of defence

Acts within min (maximum 12-24hrs)

H2CO3 produced converted to CO2, andexcreted by the lungs

Alveolar ventilation also increases as pHdecreases (Rate & Depth)



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Kidney buffer system

2nd line of defence

Can eliminate large amounts of acid

Can also excrete base

Can conserve and produce HCO3- ions Most effective regulator of pH If kidneys fail, pH balance fails

Why this is important? Because no other way to excrete these

acids (plasma conc 40nmols/day)

Reabsorption of filtered HCO3-



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Renal Acid Base Regulation Kidneys help regulate blood pH by

excreting H+ & reabsorbing HCO3-

Most of the H+ secretion occurs across thewalls of the PCT in exchange for Na+

Urine is slightly acidic because kidney

absorbs almost all the HCO3- & excrete H+

Returns blood pH back to normal range



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SECRETION OF H+ IN PCT & DCT



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7.4

Acidosis Alkalosis

Increase in H+ conc

Decrease in H+ conc

AccumulationOf Acid

Loss of base

Accumulation

Of Base

Loss of

Acid



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Acid Base Imbalance pH<7.35 Acidosis

pH>7.45 Alkalosis

Bodys response to Acid base imbalanceCOMPENSATION

If Cause is Metabolic Change in ventilation

can help RESPIRATORY COMPENSATION If cause is Respiratory change in renal

excretion can help RENAL COMPENSATION



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ACIDOSIS Principal effect CNS depression

Generalized weakness Severe acidosis causes

Disorientation

Coma

Death



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ALKALOSIS Over excitability of Central and

Peripheral Nervous system

It can cause Nervousness

Muscle spasms or Tetany

Convulsions Loss of consciousness

Death



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Respiratory Acidosis FALL IN pH

pH=pK + log HCO3

CO2

pCO2 > 45 mmHg

Cause

Depression of Resp. Centre Respiratory disorders

RenalCompensation

Renal loss of H+

Retain HCO3-



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RESPIRATORY ALKALOSIS RAISE IN pH

pH=pK + log HCO3

CO2

pCO2 < 35mmHg

Cause

Hyperventilation High altitude

Congestive heart failure

Renalcompensation

Conserve H+ ions

Excrete Bicarbonateions



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METABOLIC ACIDOSISHCO3

- deficit (<22mEq/L)

Cause

Loss of HCO3-

Diarrhea/Renal dysfunction

Accumulation of acids

Lactic acid

Ketone Bodies Failure of kidneys to

excrete H+

Respiratorycompensation

Ventilation If possible Renal

Excretion of H+ ions



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METABOLIC ALKALOSIS HCO3

- (>26mEq/L)

Cause

Excess vomiting

Use of diuretics

Severe dehydration

Respiratorycompensation

Hypoventilation



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SUMMARY pH, Acid, Base, Buffer

Importance of Body pH maintenance

Buffer systems of our body

Role of Respiratory system in pH balance

Role of Kidneys in pH maintenance

Acidosis, alkalosis Cause, symptoms, Compensation mechanisms

& therapy



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Acid Base Bal Rsl

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