Acid Base regulation

Question 1

What is normal arterial blood pH?

Answer 1

7.35 - 7.45

Question 2

How much of the acid in the blood is excreted by kidneys vs lungs?

Answer 2

lung - 99%

kidney - 1%

Question 3

What are the maximum and minimum pH ranges of blood compatible with life?

Answer 3

6.7 - 7.9

Question 4

What is normal plasma [H+]?

Answer 4

40 nmol/L^3

Question 5

What are the normal bicarbonate ranges in arterial and venous blood?

Answer 5

Arterial: 22-26mEqL-1.
Venous: 19-25mEqL-1.

Question 6

What does bicarbonate do and what is it made from?

Answer 6

Bicarbonate can act as a rapid buffer to pH changes due to metabolic acid.
Bicarbonate can be produced from volatile respiratory acid.

Question 7

How is bicarbonate reabsorbed in the PCT?

Answer 7

• Bicarbonate cannot freely be absorbed
  1. Protons are pumped out of cells and react with bicarbonate in the filtrate.
  H+ ATPase and sodium-proton antiporter are used

2. CO2 formed from the breakdown of carbonic acid passes into the cell and reacts with water
3. Bicarbonate formed in dissociation is pumped out of the cell by transporters into the interstitium and blood
   Chloride-bicarbonate exchanger and sodium-bicarbonate co-transporter used. Chloride leaves the cell into the interstitial space via chloride channel.

Na+K+ pump is can be involved to uptake potassium.

Question 8

Name two intercalating cells of the DCT/CD

Answer 8

Acid secreting (alpha) cell
Bicarbonate secreting (beta) cell

Question 9

What does the acid secreting cell do?

Answer 9

Carbonic anhydrase on the apical membrane converts bicarbonate and proton into water and carbon dioxide. Carbon dioxide enter the cells and carbonic anhydrase (diff type) converts the CO2 and H2O into bicarbonate and proton. 
Protons are removed into filtrate by:
- H+ ATPase 
- hydrogen potassium ATPase 
- sodium proton antiporter

Bicarbonate is removed into blood via chloride bicarbonate antiporter and then chloride leaves cell via a channel

Question 10

What is normal pH of urine?

Answer 10

4 to 8.5

Question 11

What does the bicarbonate secreting cell do?

Answer 11

Carbonic anhydrase converts carbon dioxide and water into bicarbonate and protons. The protons can be pumped out via H+ATPase, sodium proton transporter and hydrogen potassium ATPase into the interstitium and blood. The bicarbonate leaves the cells via chloride bicarbonate exchanger and chloride can then leave the cell via a chloride channel.

Question 12

How long do these buffer systems take to work?

Answer 12

a few hours

Question 13

How and where is bicarbonate generated?

Answer 13

Glutamine can split into bicarbonate and ammonium salts.
The ammonium salts are excreted with sodium-ammonium antiporters.
The bicarbonate is absorbed into interstitium and blood using AE1 (a chloride bicarbonate exchanger)
The Na+/K+ ATPase maintains cytosolic concentrations.

PCT

Question 14

How is the pH in the urine maintained using the acid phosphate buffer system?

Answer 14

The cell maintains the pH in the urine as the proton generated by carbonic anhydrase binds to phosphate to create acid phosphate.
H+ATPase is used to secrete the proton while the bicarbonate is absorbed using AE1.

Question 15

Describe the compensatory mechanism for respiratory acidosis

Answer 15

1. There is an initial accumulation of CO2 in arterial blood and thus a fall of pH
2. PCO2 levels stimulate the kidneys to increase HCO3- retention/production, and H+ secretion (shown as a rise in BE (more base made)
3. pH begins to normalise
4. Full compensation

Question 16

Describe the compensatory mechanism for respiratory alkalosis

Answer 16

1. There is an initial reduction of CO2 in arterial blood and thus an increase of pH.
2. PCO2 levels stimulate the kidneys to decrease HCO3- retention/production, and H+ secretion (appears as a low BE (less base made))
3. pH begins to normalise
4. Full compensation

Question 17

Describe the compensatory mechanism for metabolic acidosis

Answer 17

1. There is an initial reduction of base created or reabsorbed – low BE – and thus a drop in pH
2. Low pH stimulates hypoventilation and thus retention of CO2 and thus base
3. pH begins to normalise
4. Full compensation

Question 18

Describe the compensatory mechanism for metabolic alkalosis

Answer 18

1. There is an initial increase of base created or reabsorbed – high BE – and thus a rise in pH
2. High pH stimulates hyperventilation and thus excretion of CO2 and thus base
3. pH begins to normalise
4. Full compensation