Acid Base Balance

Question 1

What is the normal pH of arterialised blood

Answer 1

7.4

Question 2

What are the sources of H+ in the body?

Answer 2

Respiratory acid

Metabolic acids

Question 3

What are some examples of inorganic acids within the body?

Answer 3

S-containing amino acids

Phospholipids

Question 4

What are some examples of organic acids within the body?

Answer 4

Fatty acids

Lactic acids

Question 5

What is a major source of alkali in the body?

Answer 5

Oxidation of organic anions e.g citrate

Question 6

What is the role of buffers in the body?

Answer 6

Minimize changes in pH when H+ ions are added or removed

Question 7

What is the Henderson-Hasselbalch equation?

Answer 7

Defines the pH in terms of the ration of base/acid (A-/HA) NOT the absolute amounts

Question 8

What is the most important extracellular buffer?

Answer 8

Bicarbonate buffer

Question 9

What is the normal range of pH in the body?

Answer 9

7.37-7.43

Question 10

What is the pH range compatible with life?

Answer 10

7. 0-7.6 (UK)

6. 8-7.8 (US)

Question 11

What is the normal value of pCO2 in the body?

Answer 11

5.3kPa (40mmHg)

Question 12

What is the normal range of pCO2 in the body?

Answer 12

4.8-5.9 (36-44mmHg)

Question 13

What is the normal value of HCO3- in the body?

Answer 13

24mmoles/L

Question 14

What is the normal range of HCO3- in the body?

Answer 14

22-26

Question 15

How is H+ eliminated from the body?

Answer 15

Kidneys

Question 16

What are some other buffers in the ECF?

Answer 16

Plasma proteins (Pr- + H+  HPr 
Dibasic phosphate (HPO42- + H+  H2PO4)

Question 17

What are some the intracellular buffers?

Answer 17

Proteins
Organic and inorganic phosphates
Haemoglobin

Question 18

What is the main effect of buffering H+ ions by ICF buffers?

Answer 18

Changes in plasma electrolytes

Question 19

What is the effect of an increase in H+ in acidosis?

Answer 19

Hyperkalaemia. depolarisation of excitable tissues, ventricular fibrillation and death

Question 20

How do the kidneys regulate HCO3-?

Answer 20

Reabsorbing filtered HCO3-

Generating new HCO3-

Question 21

What is kidney regulation of HCO3- dependent on?

Answer 21

Active H+ ion secretion from the tubule cells into the lumen

Question 22

What is the mechanism for the reabsorption of HCO3- by the kidneys?

Answer 22

Active H+ secretion from the tubule cells
Coupled to passive Na+ reabsorption
Filtered HCO3- reacts with secreted H+
Changes into CO2 and H2O in the presence of carbonic anhydrase on the luminal membrane
CO2 freely permeable, enters cell
Dissociates into H+ and HCO3-
HCO3- pass into peritubular capillaries with Na+

Question 23

Where in the kidneys does HCO3- reabsorption occur?

Answer 23

Proximal tubule

Question 24

What are the pH limits of urine in humans?

Answer 24

4.5-5 (min)

8 (max)

Question 25

What is titratable acidity?

Answer 25

Several weak acids and bases act as buffers

Question 26

Where does titratable acidity principally occur?

Answer 26

Distal tubule

Question 27

What is titratable acidity dependent on?

Answer 27

PCO2 of the blood

Question 28

What is ammonium excretion a response to?

Answer 28

Major adaptive response to an acid load, generates new HCO3- and excretes H+

Question 29

What does respiratory acidosis result from?

Answer 29

Reduced ventilation, retention of CO2

Question 30

What are the acute causes of respiratory acidosis?

Answer 30

Drugs which depress the medullary respiratory centres (barbiturates, opiates) Obstructions of major airways

Question 31

What are the chronic causes of respiratory acidosis?

Answer 31

Lung disease (Bronchitis, emphysema, asthma)

Question 32

What is the response to respiratory acidosis?

Answer 32

Protect pH so increase HCO3-

Question 33

What does respiratory alkalosis result from?

Answer 33

Fall in pCO2, increased ventilation and CO2 blow off

Question 34

What are the acute causes of respiratory alkalosis?

Answer 34

Voluntary hyperventilation Aspirin First ascent to altitude

Question 35

What are the chronic causes of respiratory alkalosis?

Answer 35

Long term residence at altitude

Question 36

What is the response to respiratory alkalosis?

Answer 36

Protect pH so decrease HCO3-

Question 37

What does metabolic acidosis result from?

Answer 37

Decrease HCO3- from increased buffering of H+ or direct loss of HCO3-

Question 38

What are the causes of metabolic acidosis?

Answer 38

Increased H+ production (ketoacidosis of a diabetic) Failure to excrete normal dietary load of H+ as in renal failure Loss of HCO3- as in diarrhoea