Lecture 11 and 12 Acid Base Balance

Question 1

Name primary intracellular buffers

Answer 1

Proteins
Organic phosphates
Inorgainc phosphates

Question 2

To maintain electrochemical neutrality movement of H+ must be accompanied by what

Answer 2

Cl- in red cells
or
Exchanged for a cation K+

Question 3

An increase of H+ has what effect on K+ levels

Answer 3

Increases in H+ in acidosis leads to hyperkalaemia as K+ moves out of cells into plasma to maintain electrochemical neutrality

Question 4

For metabolic acid how is H+ buffered

Answer 4

Buffered in plasma and cells with HCO3-

Question 5

For respiratory acid how is H+ buffered

Answer 5

Majority occurs within cells

Rest with plasma proteins

Question 6

How does the kidney regulate HCO3-

Answer 6

Reabsorbing filtered HCO3-
Generating new HCO3-
Both dependent on active H+ secretion

Question 7

What is the average GFR in litres per day

Answer 7

180

Question 8

What is the net production of urine

Answer 8

50-100 mmoles H+ per day

Question 9

What is the main buffer in urine

Answer 9

dibasic phosphate, HPO4^2-, also uric acid and creatinine.

Question 10

The process of generation of new HCO3- in the distal tubule is dependent on what

Answer 10

PCO2

Question 11

Describe the generation go HCO3- in the distal tubule

Answer 11

1. A Na+ from Na2HPO4 is reabsorbed from the lumen into the tubule cells in exchange for secreted H+
2. Co2 from the blood combines with H20 to form carbonic acid which dissociates to form H+ and Hco3-
3. New HCo3- is absorbed into the blood along with Na+
4. Excreted H+ combines with HPO4^2- to form H2PO4- which is excited

Question 12

Describe ammonium excretion

Answer 12

1. NH3 is produced by deamination of glutamine by renal glutaminase
2. NH3 moves into tubule and combines with excreted H+, Cl- to from NH4Cl which is excreted
3. Generation of new HCO3-. CO2 from PT capillaries combines with H2o to form carbonic acid which dissociates
4. Hco3- is reabsorbed with Na+
5. H+ is secreted

Question 13

What effect does intracellular pH fall have on renal glutaminase

Answer 13

increase in renal glutaminase activity and more NH4+ produced and excreted to reduce acid load

Question 14

How many days does it take for NH4+ production to reach maximum effect

Answer 14

4-5 days

Question 15

Describe respiratory acidosis

Answer 15

pH has fallen and it is due to a respiratory change, so Pco2 must have increased. Respiratory acidosis results from reduced ventilation and retention of CO2

Question 16

What are causes of respiratory acidosis

Answer 16

Acute: Drugs that depress medullary respiratory centres- Barbiturates and Opiates
Chronic: Emphysema, asthma, bronchitis

Question 17

Why is there an increase in NH3 in respiratory acidosis

Answer 17

Increase secretion of H+ and HCO3-

Question 18

Describe respiratory alkalosis

Answer 18

• Alkalosis of respiratory origin so must be due to a fall in Pco2 and this can only occur through increased ventilation and CO2 blow-off

Question 19

What are the causes of respiratory alkalosis

Answer 19

• Acute: voluntary hyperventilation, aspirin, first ascent to altitude
• Chronic: long term residence at altitude,  Po2 to < 60mmHg (8kPa) stimulates peripheral chemoreceptors to increase ventilation.

Question 20

What is the consequence of reduced PCO2 in reparatory alkalosis on H+ secretion and HCO3- reabsorption

Answer 20

Less PCO2
Less H+
Less H+ to combine with HCO3- and less is reabsorbed so HCO3- is lost in urine

Question 21

Describe metabolic acidosis

Answer 21

Reduced HCO3-

due to increased buffering H+ or direct loss of HCO3-

Question 22

What are the causes of metabolic acidosis

Answer 22

Increase H+ production in ketoacidosis or lactic acidosis
Failure to excrete normal dietary load of H+ due to renal failure
Loss of HCO3- in diarrhoea or reabsorption failure

Question 23

Causes of metabolic alkalosis

Answer 23

Increase in H+ loss due to vomiting of gastric secretionsIncrease in renal H+ loss- aldosterone excess, excess liquorice
Massive blood transfusion (blood bank contains citrate which is converted to HCO3-)

Question 24

Between acute and chronic respiratory acidosis an an increase in PCo2 would have a smaller decrease in pH for which one

Answer 24

There is a smaller decrease in pH in chronic respiratory acidosis than in acute respiratory acidosis.
Due to 4-5 days delay of NH3 production

Question 25

What is the normal range of anion gap

Answer 25

14-18mmoles/L

Question 26

When is it useful to measure the anion gap

Answer 26

Metabolic acidosis

Question 27

What are the 2 types of metabolic acidosis

Answer 27

In one there is no change from normal and in the other the anion gap increases.

Question 28

If the metabolic acidosis is due for example to a loss of bicarbonate from the gut is there an anion gap? Explain?

Answer 28

then the reduction of bicarbonate is compensated by an increase in chloride and so there is no change in anion gap

Question 29

If the metabolic acidosis is due to lactic or diabetic acidosis is there an anion gap? why?

Answer 29

the reduction in bicarbonate is made up by other anions such as lactate, acetoacetate, -OH butyrate and so the anion gap is increased

Question 30

• pH = 7.32 (low), [HCO-3]= 15 mM (low) , PCO2 = 30mmHg (4kPa) (low)

What acid/base disturbance does this patient have

Answer 30

• Metabolic acidosis

Question 31

pH = 7.32 (low), [HCO-3]= 33 mM (high), PCO2 = 60mmHg (8kPa) (high)

What acid/base disturbance does this patient have

Answer 31

• Chronic Respiratory Acidosis

Question 32

• pH = 7.45 (high), [HCO-3] = 42 mM (high), PCO2 = 50mmHg (6.7kPa) (high)

What acid/base disturbance does this patient have

Answer 32

• Metabolic Alkalosis