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Flashcards in Renal Control Of pH Deck (39)
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0

Normal range of pH?

7.38-7.42

1

What are the clinical effects of alkalaemia?

Lowers free Ca2+, increasing excitability of nerves
Above 7.45 - causes paraesthesia and tetany

2

Why does alkalaemia cause hypocalcaemia?

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

3

What are the mortality rates if pH rises above
-7.55
-7.65

pH > 7.55 = 45% mortality
pH > 7.65 = 80% mortality

4

Clinical effects of acidaemia?

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

5

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

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

pK = 6.1

6

What does pH depend on?

[HCO3] : pCO2 ratio

7

How is the pH buffered?

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

8

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

20:1

9

How does respiratory acidaemia occur?

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

10

How does respiratory alkalaemia occur?

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

11

In general, how does the kidney control pH

By controlling HCO3- concentration

12

How do the kidneys compensate for respiratory acidaemia?

Increase [HCO3-]

13

How do the kidneys compensate for respiratory alkalaemia?

Decreasing HCO3 concentration

14

How does metabolic acidosis occur?

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

15

How can metabolic acidosis be compensated?

Increasing ventilation to reduce pCO2

16

What detects changes in pH?

Chemoreceptors

17

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

Vomiting

18

What processes can cause respiring tissues to produce acid?

Metabolism of amino acids
Production of ketones

19

How can metabolic alkalosis be compensated?

Can only be partially compensated
Decrease ventilation

20

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

Proximal convolute tubule - 80-90%
Thick ascending limb and loop of Henle - remainder

21

How much HCO3- is filtered each day?

4500 mmol

22

How is HCO3 reabsorbed from the tubule?

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

23

How is HCO3- created in the proximal tubule?

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

24

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

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

25

What is H+ buffered by in the tubule?

Filtered phosphate
Excreted ammonia to form ammonium

26

What is the minimum urine pH?

4.5

27

What is a titratable acid?

Can freely gain H+ in an acid-base reaction

28

What is the total acid excretion rate?

50-100mmol H+/day

29

How can acidosis lead to hyperkalaemia?

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