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MD3002 Physiology > Bicarbonate > Flashcards

Bicarbonate Flashcards

1
Q

What is the principal buffer of ECF and blood?

A

Bicarbonate

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2
Q

What is the chemical equation relating to acid base balance and bicarbonate inn the body?

A

CO1 + H2O H2CO3 H+ + HCO3-

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3
Q

How is pH calculated (write out the equation)?

A

pH ~ HCO3-/pCO2

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4
Q

What happens to bicarbonate levels in a metabolic acidemia?

A

Fall in HCO3-

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5
Q

For every bicarbonate ion secreted into the gut below the pylorus what is secreted into the bloodstream?

A

H+ ion secreted into bloodstream

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6
Q

For every H+ ion secreted into the stomach above the pylorus what is secreted into the bloodstream?

A

HCO3- secreted into bloodstream

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7
Q

Overall what is substance is secreted into the bloodstream more from the gut the bicarbonate or protons?

A

Acid (so if nothing were to happen i.e kidneys did not exist the body would become more acidic)

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8
Q

What are the 4 ways by which the kidney controls bicarbonate?

A
  • Bicarbonate filtration
  • Bicarbonate reabsorption
  • Bicarbonate regeneration by:
    Titratable acid excretion
    Ammonium excretion
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9
Q

What is the pH at the start of the proximal tubule?

A

~ 7.4

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10
Q

What is the GFR?

A

180 litres/day

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11
Q

What is the pH at the thick descending limb?

A

6.9

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12
Q

What is the pH at the collecting duct?

A

4.5

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13
Q

What is the normal plasma bicarbonate?

A

24 mmol/l

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14
Q

Where is 85 - 90% of filtered bicarbonate reabsorbed?

A

Proximal convoluted tubule

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15
Q

Where is the remaining 10 - 15% of bicarbonate reabsorbed?

A

Distal convoluted tibule and collecting tubule

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16
Q

How does bicarbonate reach the blood?

A
  • CO2 diffuses from the tubular lumen into the tubular cells
  • Carbonic anhydrase converts CO2 converts to CO2 to bicarbonate
  • Bicarbonate then diffuses into blood
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17
Q

How is H+ excreted from the cell into the tubular lumen and what happens to it?

A
  • Inward Na+ drives H+ out (co-transporter)
  • H+ can then through carbonic anhydrase bind with HCO3- to create CO2 and H2O
  • CO2 can then diffuse into tubular cells
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18
Q

What maximises potasium inside the cell and Na+ outwith?

A

Na+/K+ATPase on the basolateral membrane

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19
Q

Where is carbonic anhydrase present?

A

In the proximal tubular lumen not in the distal

20
Q

What is bicarbonate exchanged for moving into the blood from the tubular cells?

A

Cl- ion

21
Q

What are the 2 processes by which bicarbonate is regenerated and what is more important?

A
  • Titratable acid excretion (accounts for ~ 1/3)

- Ammonium excretion (more significant)

22
Q

What is the main source of phsophate in the body?

A

Dietary (processed meat, pheasant)

23
Q

At what percentage is most of the phosphate present at a pH of 7.4?

A

80%

24
Q

What are some of the buffers in the urine?

A
  • Phosphate
  • Urate
  • Creatinine
  • Beta-hydroxybutyrate
25
Q

What buffer is produced in large quantities in diabetic ketoacidosis?

A

Beta-hydroxybutyrate

26
Q

What is the main buffer of protons in the urine?

A

Phosphate

27
Q

How much can ammonium excretion increase in the face of an acid load?

A

10x

28
Q

What amino acid does the renal tubule cell take up more of?

A

Glutamine

29
Q

What is glutamine broken down into?

A
  • Alpha-keto-glutarate then HCO3-
  • NH4+
    Process uses up protons
30
Q

How is ammonium excreted?

A

Na+ facilitated secondary active transport

31
Q

What bicarbonate regeneration mechanism can inincrease markedly?

A
  • Ammonium excretion

- NOT titratable acid excretion as it is dependant on diet so remains relatively constant

32
Q

How is respiratory acidaemia managed by the kidney?

A
  • Rise in pCO2
  • Parallel change inside the renal tubule cells
  • Intracellular acidaemia
  • Increases uptake and use of glutamine and hence ammonium excretion
  • Increasing bicarbonate regeneration
  • Low intracellular pH increases tubular proton secretion and optimum reabsorption of bicarbonate
33
Q

What is an example of a respiratory alkalaemia?

A
  • Panic attack
  • Pulmonary embolism
  • High altitude (chronic)
34
Q

How is respiratory alkalaemia managed by the kidneys?

A
  • Fall in pCO2
  • Parallel change inside the renal tubule cells
  • Intrcellular rise in pH
  • Proton secretion falls
  • Bicarbonate reabsorption falls
35
Q

What increases bicarbonate reabsorption and regeneration?

A
  • Increasing pCO2
  • Increasing H+
  • Decreasing ECF volume
  • Increasing angiotensin II
  • Increasing aldosterone
  • Hypokalaemia
36
Q

What decreases bicarbonate reabsorption and regeneration?

A
  • Decreasing pCO2
  • Decreasing H+
  • Increasing ECF volume
  • Decreasing angiotensin II
  • Decreasing aldosterone
  • Hyperkalaemia
37
Q

What is the function of carbonic anhydrase tablets which can be given at extreme altitudes?

A

Increases loss of bicarbonate and respiratory rate and tidal volume

38
Q

What happens to ammonium secretion by the tubule if kidney function is impaired?

A

Decreased (results in metabolic acaedemia)

39
Q

What are the 3 types of renal tubule acidosis?

A
  • Type 1 (distal RTA)
  • Type 2 (Proximal RTA)
  • Type 4 (Hyperkalaemic RTA)
40
Q

What is happens in type 1 (distal RTA)?

A
  • Lowers capacity to conc. H+ in distal tubule
  • pH above 5.5
  • Plasma K+ usually low
  • Normal GFR
  • Bicarbonate < 10 mmol/l
41
Q

What is happens in type 2 (proximal RTA)?

A
  • Impairs prox reabsorption of bicarbonate
  • Urine pH is variable
  • Plasma K+ usually low
  • GFR normal
  • Plasma bicarb 15-20mmol/l
42
Q

What is happens in type 4 (Hyperkalaemic RTA)?

A
  • Caused by reduced aldosterone. Inhibits NH4+ production
  • Urine pH below 5.5
  • Plasma K+ is high
  • Plasma bicarb 15-20 mmol/l
43
Q

What type of renal tubule acidosis is most common in children?

A

Type 2 (Proximal RTA)

44
Q

What type of renal tubule acidosis is most common in adults?

A

Type 4 (Hyperkalaemic RTA)

45
Q

What is the rarest type of RTA?

A

Type 1 (Distal RTA)

46
Q

How long does it take for maximal adaptation after a significant acid-base insult?

A

5-6 days

MD3002 Physiology (24 decks)

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