Bicarbonate

Question 1

What is pH preportional too?

Answer 1

Bicarbonate/pCO2

Question 2

How are the kidneys involved with bicarbonate balance?

Answer 2

• Bicarbonate filtration,
• Bicarbonate reabsorption,
• Bicarbonate regeneration via titratable excretion or ammonium excretion

Question 3

What is the normal palsma bicarbonate levels?

Answer 3

24mmol/l

Question 4

What areas of the nephron is bicarbonate reabsorbed?

Answer 4

85-90% at PCT and remaining 10-15% in the DCT or collecting tubules

Question 5

Describe the process of bicarbonate reabsorption which is common to both absorption sites

Answer 5

Bicarbonate combines with hydrogen ions to form CO2 and H2O which can be moced across tubular epithelium into epithelium cells. Within the cell CO2 and H2O dissociate into bicarbonate and hydrogen ions. Bicarbonate diffuses into blood while H+ ions diffuse into tubular epithelium.

Question 6

What is the role of carbonic anhydrase

Answer 6

Catalyses the conversion of CO2 into carbonic acid

Question 7

Describe the difference between the proximal and distal reabsorption of bicarbonate

Answer 7

Proximal - bicarbonate sodium cotransporter at basolateral membrane. At apical membrane sodium hydrogen exchanger.
Distal - Bicarbonate chloride exchanger at basolateral membrane. At apical membrane primary active transport of H+

Question 8

Describe how the titratable acid excretion works

Answer 8

Hydrogen ions within the lumen combine with buffers especially phosphate. New bicarbonate ions are made within epithelial cells which are then transported into the blood. This is a relatively constant mechanism.

Question 9

Name some other proton buffers in the urine

Answer 9

Urate, creatinine and beta hydroxybutyrate (main one is obvs phosphate)

Question 10

Describe how ammonium excretion works?

Answer 10

Glutamine is metabolised to form ammonium which combines with hydrogen ions and is excreted in the urine. This results in the generation of a new bicarbonate ion which is transported into the blood . This form of bicarbonate regeneration can be increased

Question 11

Describe what occurs in regards to bicarbonate reabsorption with respiratory acidaemia

Answer 11

1) Rise in pCO2
2) Parallel change inside the renal tubule cells
3) Intracellular acidaemia,
4) Increases uptake and use of glutamine and hence ammonium excretion,
5) Increasing bicarbonate regeneration,
6) Low intracellular pH increases tubular proton secretion and ensures optimum reabsorption of bicarbonate

Question 12

Describe what occurs in regards to bicarbonate reabsorption with respiratory alkalaemia

Answer 12

1) Fall in pCO2,
2) Parallel change inside renal tubule cells,
3) Intracellular rise in pH,
4) Proton secretion falls,
5) Bicarbonate reabsorption falls

Question 13

Name some factors that will increase bicarb reabsorption and regeneration

Answer 13

Increasing pCO2, increasing H+ and hypokalaemia

Question 14

Name some factors that will decrease bicarb reabsorption and regeneration

Answer 14

Decreasing PCO2, decreasing H+ and hyperkalaemia

Question 15

Describe the effects of decreasing ECF volume or increasing angiotensin 2?

Answer 15

It stimulates sodium reabsorption which therefore stimulates activity of the Na/H exchanger so the radio of bicarb/H+ in tubular lumen falls. There is excess H+ in the tubules and so bicarb is fully reabsorbed and new bicarb is formed

Question 16

What occurs if there is impaired kidney function

Answer 16

It can cause damage to the glomerulus and tubule which will result in metabolic acidaemia. There will be a decrease in ammonium secretion by tubule.

Question 17

If there is a mismatch between the pH of the blood and the pH of the urine then what should you suspect?

Answer 17

Renal tubule acidosis