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Renal week 3 > Physiology 8 > Flashcards

Physiology 8 Flashcards

1
Q

What are the normal values of:

  • Plasma pH
  • [HCO3-] in plasma
  • Arterial PCO2
A
  • Plasma pH - 7.35-7.45
  • [HCO3-] - 23-27
  • Arterial PCO2 - 35-45
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2
Q

What are the overall process which occur to restore normal acid-base balance ?

A

Compensation and correction

Compensation occurs first - this is the restoration of pH irrespective of what happens to pCO2 and [HCO3-]plasma

Correction is the restoration of pH and [HCO3-]p and PCO2 to normal

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3
Q

What are the 4 main classes of acid-base disturbances ?

A
  • Respiratory acidosis and alkalosis
  • Metabolic acidosis and alkalosis
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4
Q

What is the immediate response of the body to changes in acid-base balance ?

A
  • The body initally tries to use its buffer stores e.g. Hb, HCO3-
  • BUT buffer stores are depleted quickly and need replaced
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5
Q

What are respiratory acid-base disturbances essentially due to ?

A

Thinking about the equation they are due to changes in pCO2

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6
Q

Specifically what is respiratory acidosis due to ?

A

Retention of pCO2

This is mainly due to hypoventilitation caused by:

  • Chronic bronchitis
  • Chronic emphysema
  • Airway restriction (bronchial asthma, tumour)
  • Chest injuries
  • Respiratory depression
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7
Q

What are the values which indicate a respiratory acidosis ?

A
  • pH < 7.35 low
  • pCO2 > 45 high
  • H+ and HCO3- increase
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8
Q

How is a respiratory acid-base disturbance compensated for ?

A

It is compensated for by the renal system

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9
Q

Specifically how is respiratory acidosis compensated for ?

A

Due to CO2 being the drive for H+ secretion in the tubule of the kindeys:

  1. H+ secretion is stimulated
  2. All filtered HCO3- is reabsorbed (i.e. no HCO3- excretion)
  3. H+ continues to be secreted and generates titratable acid (TA) and NH4+
  4. Acid is excreted and “new” HCO3- is added to the blood

Hence compensated will have a high HCO3-

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10
Q

What is respiratory alkalosis due to ?

A

Excessive removal of pCO2

Due to hyperventilation e.g.

  • At altitude when hypoxic you hyperventilate,
  • Fevers and hysterical overbreathing also cause hyperventilation
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11
Q

Explain the values of respiratory alkalosis

A

Due to shift of the equilibrium to the left Both [H+]p and [HCO3-]p fall

Decreased H+ causes alkalosis (remember that pH is only a measure of free [H+])

Uncompensated respiratory alkalosis is indicated if;

pH > 7.45 and PCO2 < 35 mmHg

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12
Q

How is respiratory alkalosis compensated for ?

A

Due to pCO2 driving H+ secretion into the tubule of the kidneys

There will be decreased H+ secretion due to decreased pCO2

  1. This results in insufficient H+ to reabsorb the filtered HCO3-, even though the load is lower than normal
  2. HCO3- is excreted and urine is alkaline
  3. No titratable acid (TA) and NH4+ is formed, so no “new” HCO3- is generated
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13
Q

What are metabolic disturbances in acid-base balance due to ?

A

They are due to changes in H+ conc from any other source than CO2

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14
Q

Specifically what is metabolic acidosis due to ?

A

Excess H+ from any source other than CO2

E.g.

  • Ingestion of acids or acid-producing foodstuffs
  • Excessive metabolic production of H+ (e.g. lactic acid during exercise or ketoacidosis)
  • Excessive loss of base from the body (e.g. diarrhoea – loss of HCO3-)
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15
Q

What is uncompensated metabolic acidosis indicated by ?

A

pH < 7.35 and [HCO3-]p low

The low HCO3- is due to it being depleted as it buffers the excess H+

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16
Q

For metabolic acid-base disturbances what compensates for them ?

A
  • The respiratory system as its not the problem so can compensate
  • The renal system does the correction as it takes a bit longer to act than the respiratory system
17
Q

Describe how metabolic acidosis is compensated for

A

Compensated for by the respiratory system:

  1. CO2 is blown off shifting the equilibrium to the left resulting in
  2. Decreased [H+]p and [HCO3-]p
18
Q

Describe how metabolic acidosis is compensated for

A
  1. Filtered HCO3- is very low and very readily reabsorbed
  2. H+ secretion continues and produces TA & NH4+ to generate more “new” HCO3-
  3. The acid load is excreted (urine is acidic) and [HCO3-]p is restored
  4. Ventilation can then be normalised
19
Q

What is a metabolic alkalosis due to ?

A

Excessive loss of H+ from the body

E.g.

  • Loss of HCl from the stomach (vomiting)
  • Ingestion of alkali or alkali-producing foods (e.g. Ingestion of NaHCO3 as an antacid, though not a problem with modern antacids)
20
Q

What are the values which suggest metabolic alkalosis ?

A

pH > 7.45 & high [HCO3-]

21
Q

How is metabolic alkalosis compensated for ?

A
  • Decreased ventilation which causes CO2 retention
  • Causing shift of the equilibrium to the left which increases [H+] and [HCO3-]
22
Q

How is a metabolic alkalosis corrected ?

A
  1. Filtered HCO3- load is so large compared to normal that not all of the filtered HCO3- is reabsorbed
  2. No TA or NH4+ is generated
  3. HCO3- is excreted (urine is alkaline)
  4. [HCO3-]p falls back towards normal

Renal week 3 (14 decks)

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