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MD3001 - Respiratory Physiology > Acid-Base Homeostasis Respiration > Flashcards

Acid-Base Homeostasis Respiration Flashcards

1
Q

Define pKa

A

the pH at which 50% is ionised and 50% is unionised in the reaction

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2
Q

Where does the equilibrium lie in this equation and how is the equilbrium affected by changes in H+ concentration?

H2CO3 ⇔ H+ + HCO3-

A

Equilbrium lies to the right

Ratio of H2CO3:HCO3- = (1:20)

H+ rises = left

H+ falls = right

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3
Q

What is the pKa for carbonic acid/bicarbonate?

A

6.1

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4
Q

What is normal pH?

A

7.4

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5
Q

What is the main buffering agent in the plasma?

A

bicarbonate

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6
Q

What can the absolute levels of bicarbonate be changed by?

A

breathing?

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7
Q

Indicate relative to the equation what section causes respiratory or metabolic acid-base disturbances in the body

CO2 + H2O ⇔ H2CO3 ⇔ H+ + HCO3-

A

CO2 + H2O = respiratory

H+ + HCO3- = metabolic

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8
Q

What pH indicates acidosis?

A

< 7.35

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9
Q

What pH indicates alkalosis?

A

> 7.45

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10
Q

What does each line show?

A

AB = plasma pH changes as CO2 changes (respiratory)

CD = plasma pH changes when non-volatile acid is added/removed (metabolic)

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11
Q

What are the 4 major causes of acid-base disturbances?

A
  • increased CO2
  • decreased CO2
  • increased non-voltaile acid/decrease base
  • decreased non-volatile acid/increase base
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12
Q

What type of disturbance occurs when the primary change is to CO2?

A

Respiratory

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13
Q

What type of disturbance occurs when the primary change is to bicarbonates?

A

metabolic

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14
Q

What can acidosis be caused by?

A
  • Rise in PCO2
  • Fall in HCO3-
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15
Q

What can alkalsis be caused by?

A
  • Fall in PCO2
  • Rise in HCO3-
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16
Q

What are the 2 main methods used by the body to compensate for acid-base disturbances?

A
  1. respiratory system alters ventilation
  2. kidneys alter excretion of bicarbonate
17
Q

What causes respiratory acidosis?

A

Increase in PCO2 caused by:

  • Hypoventilation (less CO2 blown away)
  • ventilation:perfusion mismatch
18
Q

What biochemical changes occurs in respiratory acidosis?

A
  • increase in PCO2 causes an increase in H+; lowering the pH
  • Plasma HCO3- levels increase to compensate for increased H+
  • Renal compensation - increased HCO3- reabsoprtion and increase HCO3- production raises the pH towards normal
19
Q

What are the main causes of respiratory acidosis?

A
  • COPD
  • blocked airway - foreign body or tumour
  • lung collapse
  • injury to chest wall
  • drugs reduceding respiratory drive e.g. morphine, barbiturayes, general anaesthetics
20
Q

What causes respiratory alkalosis?

A

Results from a decrease in PCO2 generally causedby alveolar hyperventilation (more CO2 being blown off)

21
Q

What are the biochemical changes in respiratory alkalosis?

A
  • hyperventilation causes a decrease in H+ and a rise in pH
  • Renal compensation - reduced HCO3- reabsoption and reduced HCO3-​ produtcion
  • Plasma levels of HCO3-​ fall, compensating for lower H+ moving the pH back to normal
22
Q

What are the major causes of respiratory alkalosis?

A
  • increased ventilation, from hypoxic drive in pneumonia
  • diffuse interstitial lung diseases
  • high altitude
  • mechanical ventilation
  • hyperventilation:
    • brain damage
    • infection driving fever
23
Q

When does renal compensation occur?

A

When someone cannot change their respiratory rate

e.g. COPD

24
Q

Draw a diagram indicating the changes in pH and plasma HCO3- during respiratory alkalosis and acidosis

A
25
Q

Describe the changes in this graph

A
  • Normal to A:
    • lower pH and increase in bicarbonate
    • no resp. compensation
    • kidneys secrete less bicarbonate to buffer extra H+
    • kidneys secret more acid
    • PCO2 has not changed during compensation
  • Normal to C:
    • Increased pH and decrease in bicarbonaye
    • no respiratory compensation
    • Kidneys secrete less H+ and more bicarbonate
    • PCO2 has not changed during compensation
26
Q

What causes metabolic acidosis?

A

excess H+ in the body, which reduces HCO3- levles (shifts equilibirum to the left)

27
Q

What is PCO2 in metabolic acidosis?

A

Normal

28
Q

What is the respiratory compensation in metabolic acidosis? And what other mechanisms occur?

A
  • lower pH is detected by peripheral chemoreceptors, causing an increase in ventilation which lowers PCO2
  • Bicarbonate equation is driven further to the left lowering H+ and HCO3- concentration further
29
Q

What causes metabolic acidosis?

A
  • loss of HCO3- (diarrhoea)
  • Exogenous acid overloading (aspiring overdose)
  • endogenous acid production (ketogenesis)
  • failure to secrete H+ (renal failure)
30
Q

What causes metabolic alkalosis?

A

an increase in HCO3- concentration or a fall in H+

31
Q

What is the compensation for metabolic alkalosis?

A
  • increase pH detected by peripheral chemoreceptors - decreases ventilation which raises PCO2
  • Increase in H+ moves pH back towards normal
  • Respiratory compensation cannot fully correct the imbalance
32
Q

What are the causes of metabolic alkalosis?

A
  • vomitting - loss of HCl from stomach
  • Ingestion of alkali substances
  • potassium depletion (diurectic)
33
Q

Draw a diagram indicating the compensations in metabolic acidosis and alkalosis

A
34
Q

Describe this diagram

A
  • Normal to A
    • fall in pH due to addition of H+ or loss of base
    • PCO2 = initally norml
    • Low pH stimulates respiration
    • Shift from A –> B
    • PCO2 falls
    • Renal compensation not shown
  • Normal to C
    • rise in pH due to loss of H+ or addition of base
    • PCO2 = initally normal
    • Raised pH depresses respiration
    • Shift from C –> D
    • PCO2 rises
    • Renal compensation not shown

MD3001 - Respiratory Physiology (8 decks)

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