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33 Cards in this Set
- Front
- Back
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normal pH range for systemic arterial blood |
7.35-7.45 (7.4=normal) |
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acidosis |
blood pH below 7.35 |
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effects of acidosis on CNS |
depresses synaptic transmission - depressing CNS - coma |
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alkalosis |
blood pH above 7.45 |
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effects of alkalosis on CNS |
facilitation of synaptic transmission - overexcitability of PNS, then CNS - spasms, convulsions, death |
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what is pH |
-log10[H+] e.g. pH 7.0 = 10 -7 mols [H+]/L |
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what are the 3 ways metabolic production of acid produces H+ ions |
1) carbonic acid - 13,000 mmol/day 2) non-volatile acid (not from CO2) produced from protein/nutrient metabolism - 50-80 mmol/day 3) organic acids from intermediate metabolism e.g. fatty acid, ketoacids, lactic acids |
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what is volatile acid |
carbonic acid - derived from CO2 CO2 is called volatile acid because has the potential to generate H+ after hydration with water |
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what are the three lines of defence against pH disorders |
1) chemical buffers - fractions of a sec 2) adjusting ventilation (and PaCO2 - restores 50-75% of pH) - mins 3) adjusting renal acid or alkalis excretion - hrs to days (long term) |
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what are chemical buffers of pH |
intracellular and extracellular buffer systems do not get rid of H+ just bind it most effective around the pKa of the acid (the pH at which the acid is 50% ionised) |
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what are the 3 main extracellular buffer systems |
1) protein buffer system e.g. Hb and plasma proteins - limited by diet 2) phosphate buffer system e.g. in bone 3) carbonic acid - bicarbonate buffer system - in bones also |
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what is the carbonic acid - bicarbonate buffer system |
CO2 + H2O <-> H2CO3 <-> H+ + HCO3-
at pH 7.4 conc of HCO3 = 24 mmol/L conc of H2CO3 = 1.2mmol/L (20x)
pk for the reaction is 6.1 so little H2CO3 is present at physiological pH (7.4) |
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what is H2CO3 |
carbonic acid - weak acid |
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what is HCO3- |
bicarbonate ion - weak base |
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why does the carbonic acid-bicarbonate buffer system not protect against pH changes due to respiratory causes |
cannot protect against cases where there is too much or too little CO2 because CO2 and H2O combine to make H2CO3 |
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what does the bicarbonate buffer system do in response to increased H+ |
mass reaction is pushed to RHS by more H+ -> respiratory system detects increased H+ -> increases ventilation via peripheral chemoreceptors -> blow away CO2 - reduces production of H+ |
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how is CO2 regulated by buffers |
chemoreceptors in the lungs. work in seconds |
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how is HCO3- and H+ regulated by buffers |
by the kidneys - H+ excreted; HCO3- absorbed or excreted - hours/days |
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what is the relationship between pH, PaCO2 and bicarbonate ion |
pH = pK + log [base]/[acid]
pH directly proportional to [HCO3-] kidneys /[PCO2] lungs |
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respiratory acid base disturbance |
CO2 is the cause |
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metabolic acid base disturbance |
HCO3- is the main cause |
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compensation of an acid-base disturbance |
physiological response to acid-base imbalance (can be lungs or kidneys) |
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correction of acid-base disturbance |
kidneys - adjusting renal acid/alkalis excretion - takes longer |
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respiratory acidosis |
elevation of PCO2 in the blood - due to lack of removal from CO2 from the blood |
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causes of respiratory acidosis |
- emphysema - pulmonary oedema - injury to brainstem/ respiratory centres |
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treatment of respiratory acidosis |
- IV administration of bicarbonate [HCO3-] - ventilation therapy to increase exhalation of CO2 |
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respiratory alkalosis |
low arterial blood PCO2 due to increased removal of CO2 from the blood |
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causes of respiratory alkalosis |
hyperventilation caused by - high altitude - pulmonary disease - stroke - anxiety - aspirin overdose |
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renal compensation of respiratory alkalosis |
decrease in excretion of H+ and increase excretion of bicarbonate |
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treatment of respiratory alkalosis |
re-breathing expired air |
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normal H+ values at pH 7.4 |
40 nmol/L
(4 x 10-8 mol/L) |
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normal PaCO2 values |
35-45 mmHg = 4.5 - 6 kPa |
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normal HCO3- values |
22 - 26 mmol/L |
