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Intro to Clinical Biochemistry > Acid-Base > Flashcards

Acid-Base Flashcards

1
Q

What is the pH of blood?

A

7.35-7.45

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2
Q

If you blood hydrogen ion conc is >45nmol/L you are….

A

Acidaemic

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3
Q

If you blood hydrogen ion conc is <35nmol/L you are….

A

Alkalaemic

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4
Q

Describe some H+ ion turnovers from metabolic processes

A

Incomplete oxidation of energy substrates generates acid e.g. lactic acid
- Further metabolism of these intermediates consumes it e.g. gluconeogensis from lactate

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5
Q

What is a temporary imbalance of rate H+?

A

Accumulation of lactic acid during anaerobic exercise

- Dealt with using hyperventilation

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6
Q

How much CO2 is produced every 24hr?

A. 150mol
B. 1500000000000nm
C. 15000mmol
D. 190mol

A

C

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7
Q

In health what controls excretion of hydrogen matching rate of formation?

A

Pulmonary ventilation

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8
Q

What is a buffer system?

A

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

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9
Q

What is pKa and what does the value tell you?

A

Represent the negative log of the ionisation constant of an acid

  • Acids pKa <7
  • Base pKa >7
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10
Q

At what pH will the buffer be the most effective at

A

Where pKa = pH

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11
Q

What are some natural buffer systems?

A

Blood

  • bicarbonate
  • haemoglobin
  • plasma proteins

Bone

Urine

  • phosphate
  • ammonium
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12
Q

Describe bicarbonate as a buffer system.

A

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

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13
Q

What does the blood pH depend on?

A

Ratio of HCO3:CO2

20:1

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14
Q

Haemoglobin as a buffer system

A
  • 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)

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15
Q

How are plasma proteins acting as buffering systems?

A

Based on their amino acid composition, which contains both weakly acidic and basic groups.

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16
Q

How much of the non-bicarbonate buffering of plasma does the protein account for?

A. 50%
B. 65%
C. 75%
D. 95%

A

D

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17
Q

Which protein is the most predominant buffer in plasma?

A

Albumin - behaves as a weak acid due to high conc of negatively charged AA

18
Q

How does increased H+ affect bones?

A

Stimulates the bone resorption

19
Q

How does renal processes aid in acid base balance?

A

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
20
Q

How is urine acidified?

A

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

21
Q

Monohydrogen and dihydrogen phosphate are what?

A

Buffer pair at pKa 6.8

22
Q

True or false. The acid secretion in the GI tract is the main contributor to net acid production.

A

False. Acid and bicarbonate secretion is normally in balance, meaning it does not contribute to net H+ excretion

23
Q

What regulates respiratory rate?

A

Blood CO2

- Rate of CO2 elimination is equal to production

24
Q

What type of analysis sample is most appropriate for investigating gases?

A

Heparin blood sample from radial artery - measured in blood gas analyster

25
Q

What does a blood gas analyser read?

A

pH - measure of H+ conc
PO2 - partial pressure of O2 (oxygen dissolvekd in blood)
PCO2 - partial pressure of CO2 (dissolved in blood)

26
Q

Define partial pressure.

A

Pressure that an amount of gas would exert if it occupied the same volume.

27
Q

What other blood gas measurements are relevant to acid base?

A

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

28
Q

How does H2CO3 represent PCO2?

A

H2CO3 is proportional to dissolved CO2 which is proportional to PCO2

29
Q

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+)

A

B.

30
Q

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+)

A

D

31
Q

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

A

32
Q

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

A

B

33
Q

How can ventilation affect acid base balance?

A

Impaired respiratory function causes build up of CO2 in blood, but it can be counteracted by hyperventilation.

34
Q

What significance does the interrelation of the metabolic and respiratory systems have?

A

One system will compensate for the other to bring the pH back into balance

35
Q

If the lung function is compromised, what happens?

A

Build up CO2 and H+ is excreted (and bicarbonate simultaneously regenerated)

36
Q

In primary metabolic disorders, how does the lung compensate?

A

Respiratory compensation - more excretion via ventilation

37
Q

What is the anion gap?

A

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

38
Q

Advantages of anion gap?

A

Assist in assessing severity of acidosis and response to treatment.

39
Q

Disadvantages of anion gap?

A

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

40
Q

What importance does the buffer systems have in the body?

A

Temporarily mop up the excess H+ concentrations, but ultimately H+ is moped up by excretion

Intro to Clinical Biochemistry (12 decks)

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