Acid-Base Homeostasis Respiration

Question 1

Define pKa

Answer 1

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

Question 2

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

H₂CO₃ ⇔ H⁺ + HCO₃^-

Answer 2

Equilbrium lies to the right

Ratio of H₂CO₃:HCO₃^- = (1:20)

H⁺ rises = left

H⁺ falls = right

Question 3

What is the pKa for carbonic acid/bicarbonate?

Answer 3

6.1

Question 4

What is normal pH?

Answer 4

7.4

Question 5

What is the main buffering agent in the plasma?

Answer 5

bicarbonate

Question 6

What can the absolute levels of bicarbonate be changed by?

Answer 6

breathing?

Question 7

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

CO₂ + H₂O ⇔ H₂CO₃ ⇔ H⁺ + HCO₃^-

Answer 7

CO₂ + H₂O = respiratory

H⁺ + HCO₃^- = metabolic

Question 8

What pH indicates acidosis?

Answer 8

< 7.35

Question 9

What pH indicates alkalosis?

Answer 9

> 7.45

Question 10

What does each line show?

Answer 10

AB = plasma pH changes as CO₂ changes (respiratory)

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

Question 11

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

Answer 11

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

Question 12

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

Answer 12

Respiratory

Question 13

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

Answer 13

metabolic

Question 14

What can acidosis be caused by?

Answer 14

• Rise in PCO₂
• Fall in HCO₃^-

Question 15

What can alkalsis be caused by?

Answer 15

• Fall in PCO₂
• Rise in HCO₃^-

Question 16

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

Answer 16

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

Question 17

What causes respiratory acidosis?

Answer 17

Increase in PCO₂ caused by:

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

Question 18

What biochemical changes occurs in respiratory acidosis?

Answer 18

• 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

Question 19

What are the main causes of respiratory acidosis?

Answer 19

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

Question 20

What causes respiratory alkalosis?

Answer 20

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

Question 21

What are the biochemical changes in respiratory alkalosis?

Answer 21

• 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

Question 22

What are the major causes of respiratory alkalosis?

Answer 22

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

Question 23

When does renal compensation occur?

Answer 23

When someone cannot change their respiratory rate

e.g. COPD

Question 24

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

Answer 24

Question 25

Describe the changes in this graph

Answer 25

* 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

Question 26

What causes metabolic acidosis?

Answer 26

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

Question 27

What is PCO₂ in metabolic acidosis?

Answer 27

Normal

Question 28

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

Answer 28

* 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

Question 29

What causes metabolic acidosis?

Answer 29

* loss of HCO₃^- (diarrhoea) * Exogenous acid overloading (aspiring overdose) * endogenous acid production (ketogenesis) * failure to secrete H⁺ (renal failure)

Question 30

What causes metabolic alkalosis?

Answer 30

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

Question 31

What is the compensation for metabolic alkalosis?

Answer 31

* 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

Question 32

What are the causes of metabolic alkalosis?

Answer 32

* vomitting - loss of HCl from stomach * Ingestion of alkali substances * potassium depletion (diurectic)

Question 33

Draw a diagram indicating the compensations in metabolic acidosis and alkalosis

Answer 33

Question 34

Describe this diagram

Answer 34

* 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