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FunMed > Acid-Base Balance > Flashcards

Acid-Base Balance Flashcards

1
Q

Why is pH important in human physiology?

A

Controls speed of biochemical reactions by controlling speed or enzymes activity and electrical reactions

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2
Q

What does pH stand for?

A

Potential of hydrogen

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3
Q

What is an acid?

A

Can donate a hydrogen ion

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4
Q

What is a base?

A

Can accept a hydrogen ion

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5
Q

What happens when an acid (HA) is added to water?

A

Dissociates reversibly:
HA -> H⁺ + A
Yields a free H⁺ and its conjugate base (A¯)

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6
Q

What is an example of an acid in the body?

A

Gastric acid

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7
Q

What solutions in the body are close to being neutral?

A

Urine
Saliva
Blood
Tears

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8
Q

What pH is normal blood?

A
  1. 35 (venous)

7. 45 (arterial)

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9
Q

What is the name for when blood pH is below 7.35?

A

Acidosis (acidaemia)

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10
Q

What is the name for when blood pH is above 7.45?

A

Alkalosis (alkalaemia)

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11
Q

Within what blood pH range would a person die?

A

Below 6.8 and above 8.0

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12
Q

Why is abnormal blood pH dangerous?

A

Disrupts many enzyme systems and electron transport chain in mitochondria

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13
Q

Where do most hydrogen ions in the body originate from?

A

Cellular metabolism

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14
Q

What acids are produced in cellular metabolism?

A

Carbonic, sulphuric, phosphoric and others

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15
Q

What pH is the human diet?

A

Almost neutral

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16
Q

Which food group produces the most acid?

A

Protein

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17
Q

Which 3 ways can acid be produced in the body?

A 
Breakdown of food 
Metabolic activity (e.g. lactic acid in exercise)
Metabolically-produced CO2 forming carbonic acid with water
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18
Q

Which disease state involves excess acid production?

A

Diabetic keto acidosis (DKA)

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19
Q

How is carbonic acid produced in the body?

A

Aerobic respiration of glucose

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20
Q

How is lactic acid produced in the body?

A

Anaerobic respiration of glucose

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21
Q

How is sulfuric acid produced in the body?

A

Oxidation of sulfur-containing amino acids

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22
Q

How are acidic ketone bodies produced in the body?

A

Incomplete oxidation of fatty acids

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23
Q

How is phosphoric acid produced in the body?

A

Hydrolysis of phosphoproteins and nucleic acids

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24
Q

What concentration is the metabolic production of CO2 in order to lead to production of carbonic acid?

A

15 mol/d

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25
Q

What concentration is the metabolic production of lactic acid?

26
Q

What concentration is the metabolic production of acids produced by diet and metabolism (e.g. ketoacids)?

27
Q

What condition can cause formation of formic acid?

A

Methanol poisoning

28
Q

What condition can cause formation of glycolic, glyoxylic and oxalic acids?

A

Ethylene glycol poisoning

29
Q

What 4 conditions can cause formation of lactic acid?

A

Drugs/toxins, CO poisoning, hypothension/hypoxia and liver disease

30
Q

What conditions cause formation of acetoacetate?

A

Uncontrolled diabetes and starvation

31
Q

What 3 mechanisms limit changes in pH? How long does each one take to act?

A

Chemical buffer systems in blood and ICF – immediate action
The respiratory centre in the brain stem – acts within 1-3 minutes
Renal mechanisms – requires hours to days to affect pH changes

32
Q

What is a buffer?

A 
Solution that can resist pH change upon addition of acid or base 
Able to neutralise small amounts of added acid or base, thus maintaining pH of solution relatively stable 
Acts quickly (although temporarily to bind or release H⁺) 
Consist of a weak acid and the salt of that acid functioning as a weak base
33
Q

What are the 3 major chemical buffer systems in the body?

A

Bicarbonate (HCO₃¯)
Proteins (haemoglobin and albumin)
Phosphate (PO₄³¯)

34
Q

What is the anion gap?

A

Contribution of unmeasured anions to acidosis (phosphate, ketones, cations, acetate)
= [Na+]-([Cl-]+[HCO3-])
= 8-12 mEq/L

35
Q

What one substance does the respiratory centre/lungs deal with?

A

Volatile acids CO2

36
Q

How do the lungs regulate acid-base balance?

A

Eliminating or retaining CO2 by altering rate or depth of respirations

37
Q

What is normal CO2 levels in the blood?

A

35-45 mm Hg

4.7-6.0 kPa

38
Q

What can only the kidneys rid the body of?

A

Metabolic acids - e.g. phosphoric acid, uric acid, lactic acid and ketones

39
Q

What can the kidneys prevent?

A

Metabolic acidosis

40
Q

What two tasks must the kidneys accomplish in order to maintain acid-base balance?

A
  1. Reabsorption of all filtered bicarbonate

2. Excrete the acid daily load

41
Q

What three processes do the kidneys use to accomplish their tasks effectively?

A
  1. Bicarbonate reabsorption (involving sodium transport)
  2. Hydrogen secretion
  3. Excretion of hydrogen ions with urinary buffers – titratable acids (e.g. H⁺ + HPO₄²¯ -> H₂PO₄¯) and ammonium (NH₄⁺)
42
Q

How much bicarbonate does the proximal tubule reclaim each day?

43
Q

What is actively excreted in various parts of the distal kidney?

44
Q

How do the lungs eliminate acid?

A

Expiration of CO2

45
Q

How does the proximal tube eliminate acid?

A

Reabsorbs bicarbonate ions

46
Q

What two ways do the distal tubule/collecting duct eliminate acid?

A

Excretion of H+ as a titratable acid

Excretion of NH4+

47
Q

How do the lungs and kidneys compensate for acidosis?

A

Lungs increase respiratory rate

Kidneys increase bicarbonate reserve

48
Q

How do the lungs and kidneys compensate for alkalosis?

A

Lungs decrease respiratory rate

Kidneys decrease bicarbonate reserve

49
Q

What is the Henderson-Hasselbach equation?

A

pH = pKₐ + log([conjugate base]/[acid])
Where:
pH = -log[ H⁺]
pKₐ = -log(Equilibrium constant)

50
Q

What can the Henderson-Hasselbach equation be used for?

A

To find the pH of a buffer solution

To find the ratio of conjugate base to acid of the system

51
Q

What 4 things can go wrong to affect pH?

A

Bicarbonate increase
Bicarbonate decrease
CO₂ increase
CO₂ decrease

52
Q

What are the two types of acid-base disorders and what do they involve?

A
  1. Respiratory acid-base disorders
    Result when abnormal respiratory function causes rise or fall in CO₂ in ECF
  2. Metabolic acid-base disorders
    Generation of organic or fixed acids
    Anything affecting concentration of bicarbonate ions in ECF
53
Q

In what 3 ways can acid-base disturbances be diagnosed?

A

Clinical history
Physical examination
Arterial blood gas analysis

54
Q

What are the normal values of arterial blood gases?

A 
pH = 7.35-7.45
Partial pressure of oxygen (PAO2) = >11kPa or 80-100mmHg
PaCO2 = 4.7-6.0kPa or 35-45mmHg
Bicarbonate = 22-26mmol/L
Base Excess +/- 2mEq/L
55
Q

What is the respiratory indicator of acid-base imbalances?

A

PaCO2 value

56
Q

What is the metabolic indicator of acid-base imbalances?

A

HCO3 value

57
Q

What are the 4 forms of acid-base disturbance?

A

Respiratory acidosis
Respiratory alkalosis
Metabolic acidosis
Metabolic alkalosis

58
Q

What causes respiratory acidosis and how is it compensated for?

A 
CO2 retention from hypoventilation (e.g. COPD)
Renal compensation (H⁺ excretion, HCO₃¯ gain)
59
Q

What causes respiratory alkalosis and how is it compensated for?

A 
CO₂ loss from hyperventilation (anxiety or altitude) 
Renal compensation (H⁺ retention, HCO₃¯ loss)
60
Q

What causes metabolic acidosis and how is it compensated for?

A 
Gain of acid, loss of base from diarrhoea, keto-acidosis, lactic acidosis 
Respiratory compensation (pCO₂<35mmHg [HCO₃¯]<22mM)
61
Q

What causes metabolic alkalosis and how is it compensated for?

A 
Loss of acid, gain of base from vomiting, hypokalemia, ingestion of HCO₃¯ 
Respiratory compensation (pCO₂>45mmHg [HCO₃¯]>28mM)

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