Urinary 5 - Acid-base balance

Question 1

What is the normal plasma pH range?

Answer 1

7.35 - 7.45

Question 2

Define acidosis:

Answer 2

Plasma pH < 7.35

Question 3

Define alkalosis:

Answer 3

Plasma pH > 7.45

Question 4

Why is the acid-base balance of the body dependent on the kidneys and the lungs?

Answer 4

Kidneys = responsible for HCO3- (base) regulation
Lungs = responsible for CO2 (acid) regulation

Question 5

Why does Alkalosis lead to paraesthesia and/or tetany?

Answer 5

Alkalosis leads to lowered free Ca2+ (increased binding to plasma proteins), which increases neuronal excitability

Question 6

Why does alkalosis has a high mortality (if pH > 7.65)?

Answer 6

Alkalosis lowers free Ca2+ which increases neuronal excitation leading to tetany. If tetany of respiratory muscles –> lead to death

Question 7

Describe the pathophysiology of respiratory alkalosis:

Answer 7

Hyperventilation leads to hypocapnia = increased pH

Question 8

How does the body compensate for alkalosis?

Answer 8

Central chemoreceptors detect hypocapnia and reduce ventilation rate (limited by tissue O2 demand)
Kidney tubular cells decrease H+ excretion, and decrease HCO3- recovery

Question 9

What are the main causes of Metabolic alkalosis?

Answer 9

Loss of H+ - vomiting, diarrhoea, increased secretion (Aldosterone)
Shift of H+ into ICF - hypokalaemia
Increased [HCO3-] - renal failure

Question 10

Metabolic alkalosis can lead to what kind of K+ disorder?

Answer 10

HYPOkalaemia

Question 11

Define acidosis:

Answer 11

pH < 7.35

Question 12

At what point is acidosis life threatening?

Answer 12

If pH < 7.0

Question 13

Describe the pathophysiology of respiratory acidosis:

Answer 13

Hypoventilation = hypercapnia = decreased pH

Question 14

How does the body compensate for acidosis?

Answer 14

Central chemoreceptors detect decreased pH, and increase respiratory rate
Kidneys increase HCO3- recovery and production

Question 15

Where does the majority of HCO3 reabsorption occur?

Answer 15

PCT (80%)

Question 16

What enzyme catalyses the conversion of H+ + HCO3- to H2O + CO2?

Answer 16

Carbonic Anhydrase

Question 17

List the 3 ways in which the kidneys increase production of HCO3-:

Answer 17

1 - increased conversion of CO2 + H2O into H+ and HCO3- (due to increased metabolic rate = increased CO2)
2 - From amino acids in the PCT
3 - Buffering of H+ via HPO4(2-) increases conversion of CO2 + H2O into H+ and HCO3- in DCT

Question 18

What in the tubular lumen buffers H+ allowing the increased production of HCO3-?

Answer 18

HPO4(2-)

NH3

Question 19

What are the main causes of metabolic acidosis?

Answer 19

Increased metabolic production of acid - lactic acidosis, ketoacidosis, damaged muscle cells (trauma/tumour)
Ingestion of acid
Increased HCO3- loss - renal failure, diarrhoea
Decreased H+ excretion - renal failure

Question 20

What is the Anion Gap?

Answer 20

Difference between [Na+] + [K+] and [Cl-] + [HCO3-]

Question 21

What is the normal Anion Gap?

Answer 21

10-15 mM (usually less anions than cations)

Question 22

What type of acid-base disorder can cause an increased anion gap?

Answer 22

Metabolic acidosis

Question 23

A decreased anion gap is rare, but what can cause it?

Answer 23

Hypermagnesia

Paraprotein anaemia - Multiple myeloma

Question 24

Why is metabolic acidosis associated with an increased anion gap?

Answer 24

Metabolically produced acids have an associated anion (ie Lactate) which replaces HCO3- in plasma = decreased pH

Question 25

What kind of acid-base disorder is associated with HYPOkalaemia?

Answer 25

Metabolic alkalosis

Question 26

What kind of acid-base disorder is associated with HYPERkalaemia?

Answer 26

Metabolic acidosis

Question 27

Metabolic acidosis is associated with what kind of K+ disorder?

Answer 27

HYPERkalaemia