Acid Base Balance

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Acid - Base Balance

• Seminar
• Stomatology

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Acid vs. Base

• Arrhenius
• Acid H in aqueous solutionBase OH- in
  aqueous solutionAt neutrality H OH-
• Bronsted-Lowry
• Acid H donorBase H acceptorConjugate
  acid-base pairsNo concept of neutrality
• Lewis
• Acid a potential electron-pair acceptorBase
  a potential electron-pair donor

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Acid sources

• Metabolic procesess produce acids
• To keep pH the acids are
• Metabolised
• Excreted
• Carbon dioxide
• Excreted in lungs
• Potential to create an equivalent amount of
  carbonic acid
• So called respiratory acid
• Metabolic acids - lactic a., ketone bodies,
  sulphate, phosphate
• Metabolised or excreted by kidney

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Henderson-Hasselbalch Equation

• pH
• pKa log ( HCO3 / 0.03 x pCO2)

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ACID/BASE BALANCE AND THE BLOOD
OH -
H
Acidic
Alkaline (Basic)
Neutral
pH
7
0
14
Arterial Blood
Venous Blood
Acidosis
Alkalosis
DEATH
7.4
DEATH
Normal 7.35-7.45
8.0
6.8
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Response to ABB perturbation

• First defence Buffering
• Second defence Respiratory alteration in
  arterial pCO2
• Minutes, hours
• Third defence Renal alteration in HCO3-
  excretion
• days

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BUFFER SYSTEMS

• Carbonic acid/Bicarbonate Primary buffer against
  non-carbonic acid changes
• Proteins Primary ICF buffer, also ECF
• Hemoglobin Primary buffer against carbonic acid
  changes
• Phosphate Urinary buffer, also ICF

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Terminology

• Acidosis - an abnormal process or condition which
  would lower arterial pH if there were no
  secondary changes in response to the primary
  aetiological factor.
• Alkalosis - an abnormal process or condition
  which would raise arterial pH if there were no
  secondary changes in response to the primary
  aetiological factor.
• Simple (Acid-Base) Disorders are those in which
  there is a single primary aetiological acid-base
  disorder.
• Mixed (Acid-Base) Disorders are those in which
  two or more primary aetiological disorders are
  present simultaneously.
• Acidaemia - Arterial pH lt 7.36 (ie H gt 44 nM )
  
• Alkalaemia - Arterial pH gt 7.44 (ie H lt 36 nM
  )

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Disorders

• Respiratory acidosis
• Respiratory alkalosis
• Metabolic acidosis
• Metabolic alkalosis
• Respiratory disorders are caused by abnormal
  processes which tend to alter pH because of a
  primary change in pCO2 levels.
• Metabolic disorders are caused by abnormal
  processes which tend to alter pH because of a
  primary change in HCO3-.

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Sources of acidosis

• Metabolic Severe diarrhea, Diabetes mellitus,
  strenuous exercise, uremia
• Respiratory hypoventilation

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Sources of alkalosis

• Metabolic Vomiting, ingestion of alkaline drugs
• Respiratory hyperventilation

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Role of kidney in ABR

• Controls both bicarbonate recovery and proton
  excretion
• Proximal Convoluted Tubule Na-K-ATPase Na out
  of the cells gt Na in the PCT lumen into the
  cells via a Na- H antiporter gt H into lumen gt
  H2CO3
• DCT luminal carbonic acid anhydrase converts
  H2CO3 into H2O and CO2 gt enter DCT cells gt
  back-converted by a second carbonic anhydrase. 
  H secreted in the DCT by a Na -independent
  electrogenic ATPase, HCO3-recovered.  H buffered
  in the urine by inorganic phosphate, urate and
  creatinine.
• Collecting tubule phosphate secretion,
  exctretion of ammonium

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The End.