Renal Control Of pH

Question 0

What are the clinical effects of alkalaemia?

Answer 0

Lowers free Ca2+, increasing excitability of nerves

Above 7.45 - causes paraesthesia and tetany

Question 1

Normal range of pH?

Answer 1

7.38-7.42

Question 2

Why does alkalaemia cause hypocalcaemia?

Answer 2

Alkalaemia reduces solubility of Ca salts, so free Ca leaves ECF and binds to bone and proteins

Question 3

What are the mortality rates if pH rises above

• 7.55
• 7.65

Answer 3

pH > 7.55 = 45% mortality

pH > 7.65 = 80% mortality

Question 4

Clinical effects of acidaemia?

Answer 4

Hyperkalaemia
Affects many enzymes 
-reduces cardiac and skeletal muscle contractility
-reduces glycolysis in many tissues
-reduces hepatic function

Question 5

What does the Henderson-Hasselbalch equation tell us? Formula?

Answer 5

pH =
pK + log { [HCO3-] / (pCO2 x 0.23) }

pK = 6.1

Question 6

What does pH depend on?

Answer 6

[HCO3] : pCO2 ratio

Question 7

How is the pH buffered?

Answer 7

H+ ions binding to HCO3
HCO3- + H+ -> H2O + CO2
(Decreasing the pH)

Question 8

What is the normal ratio of [HCO3-] : pCO2?

Answer 8

20:1

Question 9

How does respiratory acidaemia occur?

Answer 9

Hypoventilation -> hypercapnia -> fall in pH
Ratio is altered - less than 20x amount of HCO3 than CO2
Relatively less H+ ions are buffered, pH decrease

Question 10

How does respiratory alkalaemia occur?

Answer 10

Hyperventilation -> hypocapnia -> pH increase
Fall in pCO2 means ratio is altered
Relatively more ions are buffered - pH increase

Question 11

In general, how does the kidney control pH

Answer 11

By controlling HCO3- concentration

Question 12

How do the kidneys compensate for respiratory acidaemia?

Answer 12

Increase [HCO3-]

Question 13

How do the kidneys compensate for respiratory alkalaemia?

Answer 13

Decreasing HCO3 concentration

Question 14

How does metabolic acidosis occur?

Answer 14

When respiring tissues produce acids
H+ reacts with HCO3- to produce CO2 in venous blood
Fall in HCO3- causes fall in pH

Question 15

How can metabolic acidosis be compensated?

Answer 15

Increasing ventilation to reduce pCO2

Question 16

What detects changes in pH?

Answer 16

Chemoreceptors

Question 17

What can cause plasma [HCO3-] concentration to increase?

Answer 17

Vomiting

Question 18

What processes can cause respiring tissues to produce acid?

Answer 18

Metabolism of amino acids

Production of ketones

Question 19

How can metabolic alkalosis be compensated?

Answer 19

Can only be partially compensated

Decrease ventilation

Question 20

Where is HCO3- reabsorbed in the kidneys and in what proportions?

Answer 20

Proximal convolute tubule - 80-90%

Thick ascending limb and loop of Henle - remainder

Question 21

How much HCO3- is filtered each day?

Answer 21

4500 mmol

Question 22

How is HCO3 reabsorbed from the tubule?

Answer 22

Gradient set up by Na-K-ATPase on basolateral membrane
H+ exported from cell into tubule against conc via sodium-hydrogen-exchange
H+ + HCO3- -> CO2 + H2O
CO2 enters the cell
CO2 + H2O -> H+ + HCO3-
H+ exported, HCO3- crosses basolateral membrane

Question 23

How is HCO3- created in the proximal tubule?

Answer 23

Made from amino acids
Glutamine -> α-ketoglutarate -> HCO3- + NH4+
NH4+ excreted in the urine

Question 24

Why does H+ need to be actively secreted at the distal tubule

Answer 24

No longer a gradient because all filtered HCO3- is normally recovered by now
Na+ gradient not enough to drive H+ secretion via Na-H exchange so need active secretion of H+ into the lumen by the H-ATPase
HCO3 created from metabolic CO2

Question 25

What is H+ buffered by in the tubule?

Answer 25

Filtered phosphate

Excreted ammonia to form ammonium

Question 26

What is the minimum urine pH?

Answer 26

4.5

Question 27

What is a titratable acid?

Answer 27

Can freely gain H+ in an acid-base reaction

Question 28

What is the total acid excretion rate?

Answer 28

50-100mmol H+/day

Question 29

How can acidosis lead to hyperkalaemia?

Answer 29

When cells export H+ to increase pH, they absorb K+ from the blood
Makes intracellular pH alkaline, favouring HCO3- excretion

Question 30

Give an example of some titratable acids. What are they used for?

Answer 30

Sulphuric acid
Phosphoric acid
Used to exclude ammonium (NH4+) as a source of acid
They accept protons in this case

Question 31

When might HCO3 concentration increase?

Answer 31

Persistent vomiting

Dehydration

Question 32

Why can dehydration causes metabolic alkalosis?

Answer 32

Kidneys reabsorb as much HCO3 as possible to increase osmolarity of plasma and make water follow
Can’t rely on kidneys to correct the HCO3 concentration until fluids are given

Question 33

What can cause metabolic acidosis?

Answer 33

Lactic acidosis
Ketoacidosis
Ingestion of acids
Loss of HCO3
Problem with renal excretion of acid

Question 34

What is the anion gap equation?

Answer 34

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

Question 36

What is the anion gap normally and why?

Answer 36

10-15 mmol-1

Negative proteins replace some of the HCO3- normally

Question 37

How can HCO3 reduce without affecting the anion gap?

Answer 37

Renal problems
Can reduce HCO3 without increasing anion gap
Replaced by Cl- which is included in the equation

Question 38

How does the anion gap occur?

Answer 38

In metabolic acidosis, to produce the acid, H+ and an anion are made
H+ reacts with HCO3 -> carbon dioxide which is breathed out
Therefore some HCO3 is replaced by the anion (which is not included in the equation) increasing the difference
So gap increases if anions from metabolic acid has replaced plasma HCO3-

Question 39

What transporters are involved in hydrogen excretion in the DCT?

Answer 39

Potassium-hydrogen exchange

Hydrogen-ATPase