Acid-Base Flashcards
What is the pH of blood?
7.35-7.45
If you blood hydrogen ion conc is >45nmol/L you are….
Acidaemic
If you blood hydrogen ion conc is <35nmol/L you are….
Alkalaemic
Describe some H+ ion turnovers from metabolic processes
Incomplete oxidation of energy substrates generates acid e.g. lactic acid
- Further metabolism of these intermediates consumes it e.g. gluconeogensis from lactate
What is a temporary imbalance of rate H+?
Accumulation of lactic acid during anaerobic exercise
- Dealt with using hyperventilation
How much CO2 is produced every 24hr?
A. 150mol
B. 1500000000000nm
C. 15000mmol
D. 190mol
C
In health what controls excretion of hydrogen matching rate of formation?
Pulmonary ventilation
What is a buffer system?
Consist of weak acid and conjugate base
- Addition of H+ to buffer some will combine with conjugate base and convert it to the undissociated acid
What is pKa and what does the value tell you?
Represent the negative log of the ionisation constant of an acid
- Acids pKa <7
- Base pKa >7
At what pH will the buffer be the most effective at
Where pKa = pH
What are some natural buffer systems?
Blood
- bicarbonate
- haemoglobin
- plasma proteins
Bone
Urine
- phosphate
- ammonium
Describe bicarbonate as a buffer system.
The most important buffer in the body.
- The action of bicarbonate as a buffer is unique because it forms H2CO3, which can be broken down into H2O and CO2.
- Both H2O and CO2 can be reabsorbed excreted or used in separate pathways.
- Bicarbonate is lost once it served as a buffer, but can be regenerated using a resorption in the kidneys. The uptake is possible by excreting H+ and using carbonic anhydrase to uptake it as water and carbon dioxide
HCO3 is conjugate base
What does the blood pH depend on?
Ratio of HCO3:CO2
20:1
Haemoglobin as a buffer system
- Most powerful in deoxygenated state and the proportion in this state increases during the passage of blood through capillary beds because oxygen is lost to tissues
Haemoglobin has a high capacity for binding to H+
CO2 can diffuse into the RBC for appropriate gas exchange, but it can be utilised to release HCO3 into plasma with pick up Cl- (chloride shift)
How are plasma proteins acting as buffering systems?
Based on their amino acid composition, which contains both weakly acidic and basic groups.
How much of the non-bicarbonate buffering of plasma does the protein account for?
A. 50%
B. 65%
C. 75%
D. 95%
D
Which protein is the most predominant buffer in plasma?
Albumin - behaves as a weak acid due to high conc of negatively charged AA
How does increased H+ affect bones?
Stimulates the bone resorption
How does renal processes aid in acid base balance?
Excess H+ is excreted in urine since the body is a net producer of acid. Achieved by:
- Reabsorb bicarbonate
- Excrete H+ against a steep gradient
How is urine acidified?
By active secretion of H+ by intercalated cells of the distal tubular cells and proximal collecting duct cells
- Significant acid excretion is achieved by H+ being buffered by phosphate titrating
Monohydrogen and dihydrogen phosphate are what?
Buffer pair at pKa 6.8
True or false. The acid secretion in the GI tract is the main contributor to net acid production.
False. Acid and bicarbonate secretion is normally in balance, meaning it does not contribute to net H+ excretion
What regulates respiratory rate?
Blood CO2
- Rate of CO2 elimination is equal to production
What type of analysis sample is most appropriate for investigating gases?
Heparin blood sample from radial artery - measured in blood gas analyster
What does a blood gas analyser read?
pH - measure of H+ conc
PO2 - partial pressure of O2 (oxygen dissolvekd in blood)
PCO2 - partial pressure of CO2 (dissolved in blood)
Define partial pressure.
Pressure that an amount of gas would exert if it occupied the same volume.
What other blood gas measurements are relevant to acid base?
O2 saturation- calculation to see how much oxygen is bound to hameoglobin in RBC and available to be carried through the arteries
HCO3- -directly related to the pH level
Base excess - amount of acid/base to titrate 1 litre of blood to a pH of 7.4
How does H2CO3 represent PCO2?
H2CO3 is proportional to dissolved CO2 which is proportional to PCO2
Removing bicarbonate and increasing the PCO2 will cause….
A. PO2 will increase
B. Increase in (H+)
C. Net acid excretion stays the same
D. Decrease in (H+)
B.
Removing H+ and adding bicarbonate or lowering PCO2 will cause….
A. PO2 will increase
B. Increase in (H+)
C. Net acid excretion stays the same
D. Decrease in (H+)
D
Acidosis is best described by ….
A. Low pH, raised PCO2
B. High pH, low PCO2
C. Low, pH low PCO2
D. High pH, raised PCO2
A
Alkalosis is best described by ….
A. Low pH, raised PCO2
B. High pH, low PCO2
C. Low, pH low PCO2
D. High pH, raised PCO2
B
How can ventilation affect acid base balance?
Impaired respiratory function causes build up of CO2 in blood, but it can be counteracted by hyperventilation.
What significance does the interrelation of the metabolic and respiratory systems have?
One system will compensate for the other to bring the pH back into balance
If the lung function is compromised, what happens?
Build up CO2 and H+ is excreted (and bicarbonate simultaneously regenerated)
In primary metabolic disorders, how does the lung compensate?
Respiratory compensation - more excretion via ventilation
What is the anion gap?
Sum of K+ and Na+ minus the sum of Cl- and HCO3-
- With a normal range of 6-16
Concentration of all unmeasured anions in the plasma
Advantages of anion gap?
Assist in assessing severity of acidosis and response to treatment.
Disadvantages of anion gap?
In inorgaic metabolic acidosis the infused Cl- replaces HCO3- –> normal AG
In organic acidossis, lost HCO3- is replaced by the acid anion whihc is not normally measured –> AG increased
What importance does the buffer systems have in the body?
Temporarily mop up the excess H+ concentrations, but ultimately H+ is moped up by excretion
