Acid-base balance Flashcards

1
Q

How does the respiratory system produce acid?

A

Carbonic acid from CO2

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2
Q

How is acid produced metabolically?

A

Organic acid (lactic, amino, hydroxybutyric) and inorganic (sulphuric, phosphoric)

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3
Q

How does the respiratory system remove acid?

A

Ventilation removes CO2

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4
Q

How is acid removed metabolically?

A

Inorganic acids (excreted by kidneys unchanged) and organic acids (undergo liver metabolism)

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5
Q

pH

A
  • pH = -log10[H+]
  • Acid-base homeostasis aims to keep pH constant
  • Buffers act immediately
  • Respiratory acts rapidly (minutes to hours) - normally self-regulated
  • Renal is slow (hours to days)
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6
Q

pH buffers

A
  • Proteins: albumins (ECF) and haemoglobin (ICF)
  • Phosphate (ICF): HPO42- + H+ < = > H2PO4-
  • Carbonic acid/bicarbonate system in ECF
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7
Q

What is the main ECF buffer?

A

Carbonic acid/bicarbonate

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8
Q

Henderson-Hasselbalch equation

A

pH = pKa + Log (HCO3- / H2CO3)

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9
Q

Equation for carbonic acid/bicarbonate buffer

A

H2O + CO2 = H2CO3 = H+ + HCO3-

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10
Q

What does PCO2 represent?

A

Respiratory component of acid-base balance

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11
Q

How does the renal buffer change pH

A

Alters H+ absorption

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12
Q

Function of intercalated cells

A

Determine final urine acidity in DCT

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13
Q

What is acidosis?

A

Impaired acid excretion

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14
Q

How is sodium reabsorbed?

A

H2CO3 dissociates to form H+ ions
Na+/H+ anti porter moved H+ out of tubular cell and Na+ in
Co-transport mechanism moves Na+ and HCO3- into interstitial fluid

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15
Q

+ve BE

A

Metabolic alkalosis

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16
Q

-ve BE

A

Metabolic acidosis (base deficit)

17
Q

Anion gap

A
  • Identify cause of metabolic acidosis as being disturbance of organic (raised anion gap) and inorganic acids (normal anion gap)
  • Total cations must = anions
  • Difference between cations and anions is mainly albumin
18
Q

Acid-base compensation

A
  • If one system fails, the other compensates
  • Speed depends on system involved
  • Respiratory = rapid
  • Metabolic = slow
  • Moves pH towards normal but never to normal if underlying disease still present
  • Respiratory compensation: increased H+ acts on peripheral chemoreceptors to increase Vmin → H+ in blood can’t cross BBB
  • Metabolic compensation: increased CO2 means more HCO3- retained
19
Q

Indicator of metabolic acidosis

A

Decreased HCO3-

20
Q

Indicator of respiratory acidosis

A

Increased CO2

21
Q

Indicator of respiratory alkalosis

A

Decreased CO2

22
Q

Indicator of metabolic alkalosis

A

Increased HCO3-