Acid Base Balance Flashcards
What is the normal pH of arterialised blood
7.4
What are the sources of H+ in the body?
Respiratory acid
Metabolic acids
What are some examples of inorganic acids within the body?
S-containing amino acids
Phospholipids
What are some examples of organic acids within the body?
Fatty acids
Lactic acids
What is a major source of alkali in the body?
Oxidation of organic anions e.g citrate
What is the role of buffers in the body?
Minimize changes in pH when H+ ions are added or removed
What is the Henderson-Hasselbalch equation?
Defines the pH in terms of the ration of base/acid (A-/HA) NOT the absolute amounts
What is the most important extracellular buffer?
Bicarbonate buffer
What is the normal range of pH in the body?
7.37-7.43
What is the pH range compatible with life?
- 0-7.6 (UK)
6. 8-7.8 (US)
What is the normal value of pCO2 in the body?
5.3kPa (40mmHg)
What is the normal range of pCO2 in the body?
4.8-5.9 (36-44mmHg)
What is the normal value of HCO3- in the body?
24mmoles/L
What is the normal range of HCO3- in the body?
22-26
How is H+ eliminated from the body?
Kidneys
What are some other buffers in the ECF?
Plasma proteins (Pr- + H+ HPr Dibasic phosphate (HPO42- + H+ H2PO4)
What are some the intracellular buffers?
Proteins
Organic and inorganic phosphates
Haemoglobin
What is the main effect of buffering H+ ions by ICF buffers?
Changes in plasma electrolytes
What is the effect of an increase in H+ in acidosis?
Hyperkalaemia. depolarisation of excitable tissues, ventricular fibrillation and death
How do the kidneys regulate HCO3-?
Reabsorbing filtered HCO3-
Generating new HCO3-
What is kidney regulation of HCO3- dependent on?
Active H+ ion secretion from the tubule cells into the lumen
What is the mechanism for the reabsorption of HCO3- by the kidneys?
Active H+ secretion from the tubule cells
Coupled to passive Na+ reabsorption
Filtered HCO3- reacts with secreted H+
Changes into CO2 and H2O in the presence of carbonic anhydrase on the luminal membrane
CO2 freely permeable, enters cell
Dissociates into H+ and HCO3-
HCO3- pass into peritubular capillaries with Na+
Where in the kidneys does HCO3- reabsorption occur?
Proximal tubule
What are the pH limits of urine in humans?
4.5-5 (min)
8 (max)
What is titratable acidity?
Several weak acids and bases act as buffers
Where does titratable acidity principally occur?
Distal tubule
What is titratable acidity dependent on?
PCO2 of the blood
What is ammonium excretion a response to?
Major adaptive response to an acid load, generates new HCO3- and excretes H+
What does respiratory acidosis result from?
Reduced ventilation, retention of CO2
What are the acute causes of respiratory acidosis?
Drugs which depress the medullary respiratory centres (barbiturates, opiates)
Obstructions of major airways
What are the chronic causes of respiratory acidosis?
Lung disease (Bronchitis, emphysema, asthma)
What is the response to respiratory acidosis?
Protect pH so increase HCO3-
What does respiratory alkalosis result from?
Fall in pCO2, increased ventilation and CO2 blow off
What are the acute causes of respiratory alkalosis?
Voluntary hyperventilation
Aspirin
First ascent to altitude
What are the chronic causes of respiratory alkalosis?
Long term residence at altitude
What is the response to respiratory alkalosis?
Protect pH so decrease HCO3-
What does metabolic acidosis result from?
Decrease HCO3- from increased buffering of H+ or direct loss of HCO3-
What are the causes of metabolic acidosis?
Increased H+ production (ketoacidosis of a diabetic)
Failure to excrete normal dietary load of H+ as in renal failure
Loss of HCO3- as in diarrhoea
