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Respiratory System > Acid-Base Balance > Flashcards

Acid-Base Balance Flashcards

1
Q

What is the normal pH range of plasma?

A

pH 7.35 - 7.45

Anything greater 7.45 = alkalemia

Anything less 7.35 = acidaemia

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2
Q

What is the consequence of alkalemia?

A
  • Alkalemia lowers free calcium as it causes Ca2+ ions to come out of solution
  • Decreased Ca2+ concentration makes neuronal cells more excitable
  • Can lead to paraethesia and tetany
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3
Q

What are some of the consequence of acidaemia?

A
  1. Acidaemia increases plasma K+ concentration
    • ​​affects excitability of cardiac cells leading to arrhythmia
  2. Acidaemia can denature proteins affecting muscle contractility, glycolysis, hepatic function
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4
Q

What is the equation that controls plasma pH?

A
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5
Q

How do the kindneys control plasma pH?

A

By adjusting the recovery of HCO3- and actively secreting H+ ions

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6
Q

How do the lungs control plasma pH?

A

Alveolar ventilation determines pCO2 and pO2

Rate of ventilation controlled by chemoreceptors

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7
Q

In normal circumstances, why does increased acid production from metabolism not deplete HCO3-?

A
  • The kidneys recover all filtered HCO3-
  • Proximal tubules makes HCO3- from amino acids, putting NH4+ into urine
  • H+ ions excreted to lumen but reacts with HCO3- to give H2O + CO2 which can diffuse into the tubular cell
    • HCO3- enters ECF
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8
Q

Explain how the proximal tubule creates HCO3-

A
  1. Inside proximal tubule cells Glutamine → alpha- ketogluturate and NH4 +
  2. alpha- ketogluturate breaks down to HCO3- which is transported to ECF along with Na+ ions
  3. NH4+ breaks fown to NH3 (ammonia) and H+ ions
  4. Ammonia freely diffused into lumen of tubule and combines with H+ → NH4+ acting as an ion buffer
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9
Q

What is the function of ammonia throughout the kidney?

A

Ammonia acts as a buffer by binding with H+ ions

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10
Q

What is the minimum pH of urine?

A

pH 4.5

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11
Q

How do acidosis and alkalosis affect K+ ions in the nephon?

A

H+ and K+ are both cations, therefore movement of one will cause the reciprocal movement of th other

Acidosis: causes K+ to move out cell causing hyperkalaemia and decreased K+ excretion at the distal nephron

Alkalosis: causes K+ to move into cells causing hypokalaemia and increased K+ excretion at the distal nephron

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12
Q

How do changes in K+ ions lead to metabolic acidosis?

A

Metabolic acidosis caused by hyperkalaemia

Hyperkalemia causes H+ ions to move out of tubular cells which favours HCO3- excretion → metabolic acidosis

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13
Q

How do changes in K+ ions lead to metabolic alkalosis?

A

Hypokalaemia makes intracellular pH of tubular cells more acidic → causes H+ to move into tubular cells

Favour H+ excretion → metabolic alkalosis

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14
Q

What is respiratory acidosis and what would you expect to see in the blood results to confirm this?

A

Hypoventilation causing hypercapnia (increased pCO2) → equilibrium shifts right → fall in plasma pH

Blood results:

  • High pCO2
  • Normal HCO3-
  • Low pH
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15
Q

What is respiratory alkalosis and what would you expect to see in the blood results to confirm this?

A

Hyperventilation → hypocapnia (low CO2) → equilibrium shifts left → pH rises

Blood results:

  • pCO2 low
  • HCO3- normal
  • pH high
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16
Q

In respiratory acidosis and alkalosis, what is compensation? What will you see in the bloods if fully compensated?

A

To compensate for changes in pH the kidneys can alter [HCO3-]

acidosis: kidneys increase [HCO3-]

alkalosis: kidneys decrease [HCO3-]

If fully compensated pH will be normal

17
Q

How long does it take for the kidneys to compensate from respiratory acid/ alkalosis?

A

2-3 days

18
Q

What is metabolic acidosis? What will you see in the blood results to confirm this?

A

Metabolically active tissues produce H+ which reacts the HCO3- to deplete stores → pH drops

Bloods:

  • pCO2 normal
  • low [HCO3-]
  • pH low
19
Q

What is the anion gap?

A

The difference between measurable cations and anions, mainly:

([Na+] + [K+] ) - ([Cl-] + [HCO3-])

20
Q

What is the normal anion gap? In what circumstances would the gap change?

A

Normally 10-18 mmol.l-1

Gap increases if HCO3- replaced by other anions (not measurable) e.g. when lactic acid reacts with HCO3-

21
Q

Why is the anion gap unchanged in renal causes of acidosis?

A

Although less HCO3- is made, it is replaced by Cl- ions which are measurable

22
Q

How does the body compensate for metabolic acidosis and what will you see in the blood results?

A

Drop in pH detected by peripheral chemoreceptors → signal to respiratory centre to increase ventilation → decreases pCO2

Bloods:

  • normal pH
  • low pCO2
  • low HCO3-
23
Q

What happens in metabolic alkalosis?

A

[HCO3-] increases

Bloods:

  • pH high
  • pCO2 normal
  • [HCO3-] raised
24
Q

Can metabolic alkalosis be compensated?

A

Yes but only to a small extent as you cannot reduce breathing too much as pO2 needs to be maintained

25
Q

What conditions can lead to respiratory acidosis and how?

A

Type 2 respiratory failure

alveoli are not properly ventilated meaning low pO2 and high pCO2

Includes conditions: COPD, severe asthma, drug overdose and neuromuscular disease

26
Q

What can cause respiratory alkalosis?

A
  1. Hyperventilation - in anxiety / panic attacks
  2. Type 1 respiratory failure
27
Q

What conditions can lead to metabolic acidosis?

A
  • Diabeteic ketoacidosis
  • Lactic acidosis
  • Uremic acidosis in advanced renal failure
  • Severe, persisent diarrhoea
28
Q

What can lead to metabolic alkalosis?

A
  • severe, prolonged vomiting (loss of H+)
  • K+ depletion
  • Certain diuretics
29
Q

How do non-renal causes of metabolic acidosis cause hyperkalaemia?

A

Acidosis = increased H+ ions

H+ moves into cell and K+ moves out of cells cause hyperkalaemia

30
Q

How can diabetic ketoacidosis lead to total body depletion of K+?

A

K+ moves out of cells due to acidosis and osmotic diuresis means the ions are lost in urine

31
Q

How does metabolic acidosis lead to hypokalaemia?

A
  • Less H+ excretion in nephron causes more K+ to be excreted
  • K+ also moves into cells
  • Leads to hypokalaemia

Respiratory System (20 decks)

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