K8 - Acid Base Balance II- Whole body acid-base balance

Question 1

When will a person have a normal acid- base balance?

Answer 1

1. Plasma pH close to 7.4
2. [HCO3-]p close to 25 mol/l
3. Arterial PCO2 close to 40mmHg

Question 2

what is compensation?

Answer 2

if normal acid-base balance is disrupted then priority is to restore pH to 7.4 irrespective of bicarbonate levels and partial pressure of CO2

Question 3

what is correction?

Answer 3

restoration of pH and bicarbionate and PCO2 to normal

Question 4

Name two disturbances of respiratory origin

Answer 4

• respiratory acidosis (plasma pH falls)

- respiratory alkalosis (plasma pH rises)

Question 5

Name two Disturbances of non-respiratory origin

Answer 5

• metabolic acidosis (plasma pH falls)

- metabolic alkalosis (plasma pH rises)

Question 6

how the body initally limits pH changes?

Answer 6

• immediate dilution of acid or base in ECF
• blood buffers
• buffers in the ECF - bicarbonate
  stores deplete very quickly so kidney has to rectify the problem

Question 7

What can measure pH and PCO2?

Answer 7

A blood-gas analyser

Question 8

What is the name for the diagram which shows [HCO3-]p and plasma pH?

Answer 8

Davenport Diagram

Question 9

What is respiratory acidosis?

Answer 9

retention of CO2 by the body

Question 10

Give 5 examples of respiratory acidosis

Answer 10

• chronic bronchitis
• chronic emphysema
• airway restriction (bronchial asthma, tumour)
• chest injuries
• respiratory depression

Question 11

what causes respiratory acidosis?

Answer 11

CO2 retention drives equilibrium to the right

CO2 + H2O >< H2CO3 >< H+ + HCO3-

so both [H+]p and [HCO3-]p rise and the increases [H+] results in acidosis

Question 12

what range of values does respiratory acidosis occur in?

Answer 12

pH < 7.35 and PCO2 > 45 mmHg

Question 13

Is there extracellular buffering in respiratory disorders?

Answer 13

virtually none

Question 14

What stimulates H+ secretion into the filtrate to compensate for respiratory acidosis?

Answer 14

CO2 retention stimulates H+ secretion into the filtrate

Question 15

Describe the events that happen after H+ secretion is stimulated for respiratory acidosis compensation?

Answer 15

• all filtered HCO3- is reabsorbed
• H+ continues to be secreted and generates titratable acid (TA) and NH4+
• acid is excreted and “new” HCO3- is added to the blood

Question 16

Why does [HCO3-]p rise?

Answer 16

• as a result of the disorder

- as a result of the renal compensation

Question 17

What is correction process in respiratory acidosis?

Answer 17

Lowering PCO2 by restoration of normal ventilation

Question 18

how does respiratory acidosis appear on davenport diagram?

Answer 18

pH too low and bicarbonate too high

Question 19

What is respiratory alkalosis?

Answer 19

Excessive removal of CO2 by the body

Question 20

When would respiratory alkalosis occur? 3 examples

Answer 20

• low inspired PO2 at altitude
• hyperventilation (causes include fever, brainstem damage)
• hysterical over breathing

Question 21

What does respiratory alkalosis do to the buffer equation?

Answer 21

drives equilibrium to the left resulting in [H+]p and [HCO3-]p decrease

Question 22

What indicates respiratory alkalosis?

Answer 22

pH> 7.45

PCO2< 35mmHg

Question 23

what is the compensatory mechanism for respiratory alkalosis?

Answer 23

1. excessive removal of CO2 reduces H+ secretion into the filtrate
2. H+ secretion is insufficient to reabsorb the filtered bicarbonate
3. bicarbonate is excreted into the urine
4. no titratable acid or NH4+ is produced

Question 24

What does renal compensation for respiratory alkalosis do to [HCO3-]p?

Answer 24

Lowers [HCO3-]p

Question 25

What does correction require in respiratory alkalosis?

Answer 25

restoration of normal ventilation

Question 26

how does respiratory acidosis appear on davenport diagram?

Answer 26

pH too high and bicarbonate too low

Question 27

What is metabolic acidosis ?

Answer 27

Excess H+ from any source other than CO2

Question 28

Give 3 examples of metabolic acidosis

Answer 28

- ingestion of acids or acid- producing foodstuffs - excessive metabolic production of H+ (lactic acid during exercise or ketoacidosis) - excessive loss of base from the body

Question 29

In metabolic acidosis what is depleted as a result of buffering excess H+ or loss of HCO3- from the body?

Answer 29

[HCO3-] from the body

Question 30

What is metabolic acidosis indicated by?

Answer 30

pH less than 7.35 | [HCO3-]p is low

Question 31

Explain respiratory compensation for metabolic acidosis

Answer 31

1. decrease in plasma 2. pH stimulates peripheral chemoreceptors 3. ventilation is quickly increased and more carbon dioxide is blown off 4. H+ and bicarbonate both lowered as there isn't any carbon dioxide to make them

Question 32

Explain correction for metabolic acidosis

Answer 32

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

Question 33

how does metabolic acidosis appear on davenport diagram?

Answer 33

pH to low and bicarbonate too low

Question 34

What does metabolic alkalosis result in?

Answer 34

Excessive loss of H+ from the body

Question 35

Give 3 examples of metabolic alkalosis

Answer 35

- loss of HCL from the stomach (vomiting) - ingestion of alkali or alkali- producing foods (ingestion of NaHCO3 as an antacid, though not a problem with modern antacids) - aldosterone hypersecretion (causes stimulation of Na+/H+ exchange at the apical membrane of the tubule; acid secretion)

Question 36

In metabolic alkalosis what happens to [HCO3-]p as a result of loss of H+ or addition of base?

Answer 36

[HCO3-]p rises

Question 37

What is uncompensated metabolic alkalosis indicated by?

Answer 37

- pH > 7.45 | - [HCO3-]p high

Question 38

Explain Respiratory compensation for metabolic alkalosis

Answer 38

1. Increased pH slows ventilation 2. CO2 retained, PCO2 rises 3. [H+]p rises, lowering pH 4. [HCO3-]p also rises further

Question 39

In metabolic alkalosis why is not all of the filtered HCO3- reabsorbed?

Answer 39

Because HCO3- is so large compared to normal

Question 40

Explain the renal correction for metabolic alkalosis

Answer 40

- filtered bicarbonate load is so large compared to normal that not all the filtered bicarbonate is reabsorbed - no titrateable acid or NH4+ is generated - bicarbonate is excreted (alkaline urine) - bicarbonate levels fall back to normal