Physiology - Acid-Base Balance II: Whole Body Acid-Base Balance

Question 1

How can a normal acid-base blanace be described in terms of metabolic components?

Answer 1

Plasma pH - 7.35-7.45

Bicarbonate - 25mmol/l

Arterial PCO2 - 40mmHg

Question 2

What is the difference between compensation and correction in terms of acid-base balance?

Answer 2

First priority is to restore pH to 7.4 as soon as possible

Compensation is the restoration of pH irrespective of what happens to [HCO3-]p and PCO2

Correction of an A-B disturbance is restoration of pH and [HCO3-]p and PCO2 to normal

Question 3

What is the first “line of defence” against pH changes in the blood?

Answer 3

Blood buffers

Question 4

What is the role of the renal system in terms of mainatining buffer solutions?

Answer 4

As buffer stores become depleted, the kidney will reabsorb and rectify stores

Question 5

From the Henderson-Hasselbalch equation, pH is shown to be in direct proportion to what?

Answer 5

pH is in direct propertion to [HCO3-]/[CO2]

(this is the Henderson Hasselbach equation)

Question 6

In basic terms, what cause respiratory acidosis?

Answer 6

Retention of CO2 by the body

(e.g. emphysema)

Question 7

Why does CO2 retention in respiratory acidosis result in an acidosis?

Answer 7

Increased CO2 drives the equilibrium to the right producing more hydrogen ions and bicarbonate

(acidosis occurs since the buffer cannot buffer itself e.g. Hydrogen ions cannot be buffered by bicarbonate - stong acids completely dissociate in solution)

Question 8

How can an uncompensated respiratory acidosis be defined?

Answer 8

pH < 7.35 and PCO2 > 45 mmHg

Question 9

How do the kidneys compensate for a respiratory acidosis?

Answer 9

Blood PCO2 drives H+ secretion by the kidney

Therefore, CO2 retention stimulates H+ secretion into the filtrate (generates titratable acid and ammonium ions)

Bicarbonate is also retained and new bicarbonate is added

Question 10

Correct of a respiratory acidosis requires what?

Answer 10

Restoration of ventilatory function of the lungs

Question 11

How does respiratory alkalosis come about?

Answer 11

Excess removal of CO2 from the blood

(e.g. low inspired PO2 at high altitude, causes hyperventilation which lowers PCO2)

Question 12

How does a respiratory alkalosis come about?

Answer 12

Excess CO2 removal from the blood

Drive equilibrium to the left

Reduces bicarbonate concentration in the blood

Question 13

How is a respiratory alkalosis compensated for?

Answer 13

Hydrogen ion secretion is reduced

Bicarbonate is excreted in the urine

No titratable acid and ammonia is produced so less new bicarbonate is generated

Question 14

How is respiratory alkalosis corrected in full?

Answer 14

Resoration of normal ventilation

Question 15

How is a metabolic acidosis defined?

Answer 15

Excess H+ from any source other than CO2

(e.g. ingestion of acid, lactic acidosis after exercise, DKA, excessive loss of base e.g diarrhoea)

Question 16

In someone suffering from metabolic acidosis, there is a _________ level of bicarconate ions in the blood

Answer 16

In someone suffering from metabolic acidosis, there is a reduced level of bicarconate ions in the blood

Question 17

How is a metabolic acidosis compensated for?

Answer 17

Peripheral chemoreceptors are stimuated as pH lowers

Buffer reaction shifts to the left

CO2 in the blood is increased

Ventilation increases to blow off excess CO2

Question 18

How is a metabolic acidosis corrected?

Answer 18

Renal system

Bicarbonate ions are reabsorbed easily (as they are in low concentartion)

Titratable acid and ammonium ions are produced in tubular fluid and excreted in urine

New bicarbonate ions are created by this process

Ventilation can then normalise

Question 19

In a metabolic acidosis, why is respiratory compensation required?

Answer 19

Acid load cannot be excreted immediately so needs respiratory compensation until this can occur

Question 20

How is metabolic alkalosis defined?

Answer 20

Excessve acid loss from the body

(e.g. vomiting, ingestion of alkali, aldosterone hypersecretion)

Question 21

How does the respiratory system compensate for a metabolic alkalosis?

Answer 21

CO2 is retianed as breathing slows

The buffer equation shifts to the right

Hydrogen ions increase

Question 22

How is metabolic alkalosis corrected?

Answer 22

Some bicarbonate is not reabsorbed and lost in the urine

No titratable acid or ammonium ions are created and secreted

Less new bicarbonate is produced

Question 23

In respiratory acidosis, there is a ________ acid concentration and a _________ bicarbonate concentration

Answer 23

In respiratory acidosis, there is a high acid concentration and a low bicarbonate concentration

Question 24

In metabolic acidosis, there is a ________ acid concentration and a _________ bicarbonate concentration

Answer 24

In metabolic acidosis, there is a high acid concentration and a high bicarbonate concentration

Question 25

In metabolic alkalosis, there is a ________ acid concentration and a _________ bicarbonate concentration

Answer 25

In metabolic alkalosis, there is a low acid concentration and a high bicarbonate concentration

Question 26

In respiratory alkalosis, there is a ________ acid concentration and a _________ bicarbonate concentration

Answer 26

In respiratory alkalosis, there is a low acid concentration and a low bicarbonate concentration