The Role of Ventilation in Acid Base Balance Flashcards Preview

Physiology 1 - SGUL (Sem 2) > The Role of Ventilation in Acid Base Balance > Flashcards

Flashcards in The Role of Ventilation in Acid Base Balance Deck (11)
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1
Q

Why is pH homeostasis important?

A
Various factors (including pH) can denature proteins by disrupting their bonds and structure, thus impairing function.
Different enzymes can function at varying pH ranges based on the environment they have been adapted to function within.
2
Q

How is arterial pH tightly regulated?

A

The regulation of arterial pH is achieved by the presence of buffering systems (which resist changes in pH), and by regulating the level of molecules associated with acid and base production.

3
Q

How is pH homeostasis maintained when acid production increases?

A

The presence of buffers ( a weak acid and a conjugate base) ‘mops up’ the excess H+. An example of such a buffer is the bicarbonate buffering system, with H2CO3 as the weak acid and HCO3- as the conjugate base.

Any H+ formed by the addition of a strong acid reacts with a conjugate base to form a weaker acid, hence the pH remains relatively stable.

4
Q

Give examples of other buffering systems (intracellular and extracellular).

A

INTRACELLULAR:

  • phosphate buffering system
  • amino acids/ proteins
  • haemoglobin (in RBCs)

EXTRACELLULAR:

  • bicarbonate buffer system
  • plasma proteins (eg. albumin)
5
Q

What is blood pH directly proportional to?

A

pH ∝ log ([HCO3-]/PaCO2)

6
Q

How do the lungs and kidneys maintain blood pH homeostasis?

A

The kidneys regulate the levels of HCO3- (eg. regulating reabsorption/ excretion in glomerular filtrate [timeframe = days] ).

The lungs regulate the PaCO2 (eg. regulating ventilation [timeframe = minutes to hours] ).

7
Q

What is to blame if the CO2 is too high/low, or if the HCO3- is too high/low?

A

CO2 IS HIGH: respiratory acidosis
CO2 IS LOW: respiratory alkalosis

HCO3- IS HIGH: metabolic alkalosis
HCO3- IS LOW: metabolic acidosis

8
Q

For acidosis, list its arterial pH, some causes, effects and compensatory mechanisms.

A

pH: < 7.35

CAUSES:

  • hypercapnia (hypoventilation)
  • increased lactic acid (sepsis)
  • increased ketone bodies (diabetes)
  • decreased kidney acid excretion (renal failure)
  • decreased HCO3- reabsorption (renal acidosis)
  • diarrhoea (loss of HCO3- from the gut)

EFFECTS:

  • tachypnoea (rapid breathing)
  • muscular weakness
  • headaches
  • confusion
  • coma
  • cardiac arrhythmia
  • hyperkalaemia

COMPENSATORY MECHANISMS:

  • hyperventilation (decreased PaCO2) (respiratory compensation)
  • decreased HCO3- excretion (renal compensation)
9
Q

For alkalosis, list its arterial pH, some causes, effects and compensatory mechanisms.

A

pH: > 7.45

CAUSES:

  • hypocapnia (hyperventilation)
  • vomiting (loss of H+ in HCl)
  • increased kidney acid excretion (diuretics)
  • increased alkalotic agent consumption (antacids, NaHCO3)

EFFECTS:

  • bradypnoea (slow breathing)
  • muscular weakness
  • cramps
  • tetany (muscular spasms)
  • headaches
  • nausea
  • light-headedness
  • confusion
  • coma
  • cardiac arrhythmia
  • hypokalaemia

COMPENSATORY MECHANISMS:

  • hypoventilation (increased PaCO2) (respiratory compensation)
  • increased HCO3- excretion (renal compensation)
10
Q

Describe how acidosis can induce hyperkalaemia.

A

Acidosis increases the concentration of extracellular H+, which decreases the H+ concentration gradient.
This means that there is less H+ excretion via the H+-Na+ exchange. The decreased levels of intracellular Na+ affect Na+-K+ exchange, decreasing the K+ absorption into the cell.

The K+ accumulation in the serum is known as hyperkalaemia, and leads to cardiac arrhythmias and muscle weakness.

11
Q

Describe how alkalosis can induce cerebral vasoconstriction.

A

CO2 (via H+) acts as a vasodilator in blood vessles (the cerebral arteries are particularly sensitive).
However, in alkalosis (with decreased CO2 and H+ levels), there is vasoconstriciton in the cerebral arteries.
This decrease in cerebral flow leads to headaches, lightheadedness, confusion and seizures.

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