Acid base balance 1 Flashcards
Normal pH of arterial blood
7.4
What contributes to the the acidity of pH
Only FREE H+ ions
Sources of H+
Respiratory acid
Metabolic acid
What kind of acid is respiratory acid and what’s contribution to pH and why
Carbonic acid
Not normally a net contributor to increased acid because any increase in production => increased ventilation.
Problems occur if lung function is impaired.
Types of metabolic acids
Organic and inorganic acids
Function of buffers
To minimise changes in pH when H+ ions are added or removed
Most important extracellular buffer
The bicarbonate buffer
Normal range of pH
pH compatible with life
- 37-7.43
7. 0-7.6
Normal pCO2
Normal range of pCO2
- 3kPa
4. 8-5.9kPa
Normal [HCO3]
Normal [HCO3] range
24mmoles
22-26mmoles
The Henderson-Hasselbalch Equation
pH ?directly proportional? [HCO3-]/ PCO2
How is H+ eliminated from the body
Via kidneys
2 other buffers in the ECF
Plasma proteins Pr-
Dibasic phosphate HPO4^2-
Primary intracellular buffers are
Proteins
Organic and inorganic phosphates
In erythrocytes haemoglobin.
What happens in acidosis with respect to K+
Moves out of cell 》hyperkalaemia 》depolarisation of excitable cells 》V Fib 》 death
What organ(s) provide an additional store of buffer and what condition is this important to remember in and why
Carbonate found in bone
In chronic acid loads like renal failure bone wasting is seen
Why does acidosis lead to hyperkalaemia (very important)
Because of the need to maintain electrochemical neutrality, K+ is pumped out of cells (to compensate for increased H+)
What two organs are 1° responsible for maintaining arterial pH at 7.4
Lungs and kidneys
How does the kidney regulate [HCO3-]
Reabsorbing it and making new HCO3
Minimum and maximum urine pH
4.5-5
~8.0
What does renal glutaminase do
Deaminates glutamine producing ammonia and eventually excreting H+ in the form of Ammonium (NH4+)
Effect of decreased intracellular pH on glutaminase
Increases renal glutaminase activity 》more ammonium produced and excreted (more H+ excreted)
What causes acidosis or alkolosis in respiratory disorders and renal disorders
Respiratory = pCO2 Metabolic/Renal = [HCO3-]
What does respiratory acidosis result from
Reduced ventilation 》increased CO2 retention
Causes of respiratory acidosis
Acute: Drugs which depress the medullary respiratory centres eg opiates
Obstruction of major airways.
Chronic: lung disease eg bronchitis, emphysema, asthma.
Causes of respiratory alkalosis
Acute: Voluntary hyperventilation
Aspirin
First ascent to altitude
Chronic: Long term residence at altitude decreases Po2 to < 60mmHg (8kPa) stimulates peripheral chemoreceptors to increase ventilation.
Causes of metabolic acidosis
- Increased H+ production, as in ketoacidosis of a diabetic
- Failure to excrete the normal dietary load of H+ eg renal failure.
- Loss of HCO3- eg diarrhoea 》failure to reabsorb intestinal HCO3-
Respiratory response to acidosis
Increased ventilation via DEPTH rather than rate
Name for very deep breathing and its clinical significance
Kussmaul breathing
Suggests renal failure or ketoacidosis
