Session 5: Acid-Base Balance

Question 1

Give the range of normal plasma pH

Answer 1

7.35-7.45

Question 2

Above what plasma pH is alkalaemia?

Answer 2

7.45

Question 3

Below which plasma pH is acidaemia?

Answer 3

7.35

Question 4

Which condition is more life threatening: alkalaemia or acidaemia?

Answer 4

Alkalaemia

Question 5

If pH rises to 7.55 what is the mortality?

Answer 5

45%

Question 6

If pH rises to 7.65 what is the mortality?

Answer 6

80%

Question 7

How does alkalaemia increase neuronal excitability?

Answer 7

Lowers free calcium by making Ca2+ come out of solution

Question 8

What are the two major symptoms of alkalaemia?

Answer 8

Parasthesia

Tetany

Question 9

How does acidaemia cause arrhythmia?

Answer 9

Increased plasma potassium ion concentration

Question 10

How does acidaemia affect enzymes?

Answer 10

Proteins damaged by increased [H+]

Question 11

Below what pH is considered life threatening?

Answer 11

7.0

Question 12

How do the kidneys control pH?

Answer 12

Vary the recovery of HCO3- and actively secrete H+ ions

Question 13

How do the lungs control pO2 and pCO2?

Answer 13

Altering rate of ventilation

Question 14

What organ controls the [HCO3-]?

Answer 14

The kidneys

Question 15

What process produces acid in the body?

Answer 15

Metabolism

Question 16

In which region of the kidney is HCO3- mostly recovered?

Answer 16

PCT

Question 17

Which membrane is carbonic anhydrase located on in the tubular cells?

Answer 17

Apical membrane

Question 18

What role does the Na+K+ ATPase have in renal recovery of HCO3-?

Answer 18

Sets up a Na+ concentration gradient across the basolateral membrane

Question 19

What does the HCO3-Na+ transporter do?

Answer 19

Transports 3 HCO3- and an Na+ ion out into the ECF

Question 20

How can HCO3- be created in the kidneys?

Answer 20

Breakdown of glutamine to α-ketoglutarate

Question 21

What else apart from HCO3- is released from breakdown of amino acids?

Answer 21

Two NH4+ ions

Question 22

Why does NH4+ get ‘trapped’ in the lumen?

Answer 22

It is charged so cant cross the membrane

Question 23

What two compounds act to buffer H+ in the kidneys?

Answer 23

Ammonia and phosphate

Question 24

Why is H+ produced in the kidneys?

Answer 24

Reaction between CO2 and water

Question 25

How does a fall in pH affect ammonium production?

Answer 25

Increases it

Question 26

What buffering system is mainly used in the proximal tubule?

Answer 26

Ammonium

Question 27

What buffering system is used in the distal tubule of the kidney?

Answer 27

Phosphate

Question 28

Where is ammonium mostly created?

Answer 28

In the PCT

Question 29

What is the minimum safe pH of urine?

Answer 29

4.5

Question 30

What is the range of average total acid secretion a day?

Answer 30

50-100mmol

Question 31

How does acidosis cause hyperkalaemia?

Answer 31

Causes K+ to move out of the cells and so less is excreted at the distal nephron

Question 32

How does alkalosis cause hypokalaemia?

Answer 32

Cause enhanced excretion of K+ at the distal nephron as it moves into the cells

Question 33

How is metabolic alkalosis related to hypokalemia?

Answer 33

H+ moves into the tubular cells and lowers the pH

Question 34

How does hyperkalaemia cause metabolic acidosis?

Answer 34

H+ ions move out of the cells and into the blood

Question 35

What is respiratory acidosis characterised by?

Answer 35

Low pH High pCO2 Normal HCO3-

Question 36

How will hyperventilation affect pH?

Answer 36

Causes a rise in pH due to hypocapnia

Question 37

What is respiratory alkalosis characterised by?

Answer 37

Raised pH Low pCO2 Normal HCO3-

Question 38

How will the kidneys respond to compensate for respiratory acidosis?

Answer 38

Increase [HCO3-]

Question 39

How is compensated respiratory acidosis characterised?

Answer 39

High pCO2 Raised [HCO3-] Relatively normal pH

Question 40

How is compensated respiratory alkalosis characterised?

Answer 40

Low pCO2 Lowered [HCO3-] Relatively normal pH

Question 41

Why is metabolic acidosis different to respiratory acidosis?

Answer 41

There is no change in pCO2 but a fall in [HCO3-] as it reacts with the acid produced

Question 42

How do you calculate the anion gap?

Answer 42

([Na+]+[K+]) - ([Cl-]+[HCO3-])

Question 43

Give the normal range for the anion gap

Answer 43

10-18mmol/L

Question 44

When will the anion gap increase?

Answer 44

When HCO3- is replaced by other anions

Question 45

Why do renal causes of acidosis not change the anion gap?

Answer 45

Cl- replaces the fall in HCO3- production

Question 46

What are the characteristics of metabolic acidosis?

Answer 46

Low pH Low HCO3- Normal pCO2

Question 47

What is compensated metabolic acidosis characterised by?

Answer 47

Near normal pH Low pCO2 Low HCO3-

Question 48

What are the characteristics of metabolic alkalosis?

Answer 48

Raised pH Raised HCO3- Normal pCO2

Question 49

Why can’t a reduction in breathing compensate for metabolic alkalosis?

Answer 49

Need to maintain pO2

Question 50

What conditions can lead to respiratory alkalosis?

Answer 50

Type 1 respiratory failure Type 2 respiratory failure Hyperventilation

Question 51

What is type 1 respiratory failure?

Answer 51

Hyperventilation in response to long term hypoxia

Question 52

What happens to the pCO2 in type 2 respiratory failure?

Answer 52

Increases

Question 53

How does pCO2 change in type 1 respiratory failure?

Answer 53

Falls

Question 54

How is chronic hyperventilation compensated for?

Answer 54

Drop in [HCO3-]

Question 55

What does an increase in the anion gap indicate?

Answer 55

Metabolic production of an acid

Question 56

Give three ways in which there may be metabolic production of an acid

Answer 56

Ketoacidosis Lactic acidosis Uraemic acidosis

Question 57

What is type 1 renal tubular acidosis?

Answer 57

Inability to pump out H+ (affects distal tubule)

Question 58

What does type 2 renal tubular acidosis cause?

Answer 58

Problems with HCO3- reabsorption

Question 59

How will the anion gap be changed in renal tubular acidosis?

Answer 59

Unaltered

Question 60

How can severe persistent diarrhoea lead to metabolic acidosis and why is there no change to the anion gap?

Answer 60

Loss of HCO3- but this is replaced by Cl-

Question 61

How do non renal causes of metabolic acidosis affect K+ at the kidneys?

Answer 61

Increases their reabsorption

Question 62

Why is there a total body depletion of K+ in diabetic ketoacidosis?

Answer 62

K+ moves out of cells and is lost in urine due to osmotic diuresis

Question 63

What effect does insulin have on movement of K+?

Answer 63

Causes it to move into the cells of the tubule

Question 64

What may severe prolonged vomiting lead to and why?

Answer 64

Metabolic acidosis because of loss of H+

Question 65

How is volume depletion avoided in metabolic acidosis?

Answer 65

Na+ H+ exchanger continues to operate (Na+ recovered and H+ excreted)