Physiology

Question 1

[RENAL]

What is a volatile acid? What is a non-volatile acid?

Answer 1

Volatile Acid - CO2

Non-volatile Acid - organic acids (e.g. sulfuric, phosphoric)

Question 2

[RENAL]

What is the action of carbonic anhydrase?

Answer 2

Combines CO2 and H2O to H2CO3 (carbonic acid)

Question 3

[RENAL]

What does the pK of an acid-base buffer mean?

Answer 3

pK is the affinity of the buffer for protons

Question 4

[RENAL]

What is the Henderson-Hasselbach Equation? What does it mean?

Answer 4

pH = pK + log [A-]/[HA]

pH is dependent on the buffer’s pK and on the concentrations of the base [A-] and acid [HA]

If the concentrations of [A-] and [HA] are the same, then pH = pK

Question 5

[RENAL]

What is the acid-base titration curve? What does it say?

Answer 5

Curve plotting the concentration of the [A-] and [HA] forms as a function of pH

Buffers are most effective in the middle, linear part of the curve (nearest to the pK)

Question 6

[RENAL]

Describe the process of reabsorption of filtered HCO3-

Answer 6

1. H20 + CO2 produced in proximal tubule cells
2. Intracellular carbonic anhydrase creates H2CO3
3. H2CO3 dissociates into H+ and HCO3-
4. HCO3- is reabsorbed into blood, H+ is excreted via Na-H+ exchanger
5. H+ binds to HCO3- in the lumen
6. Brush border carbonic anhydrase creates H2CO3
7. H2CO3 dissociates into H2O and CO2
8. H2O and CO2 reabsorbed, cycle repeats.

Question 7

[RENAL]

What are the 4 factors that regulate reabsorption of filtered HCO3-?

Answer 7

1. Filtered load of HCO3-
2. pCO2
3. ECF volume
4. Angiotensin II

Question 8

[RENAL]

What is contraction alkalosis?

Answer 8

Decrease in ECF volume leads to increase in HCO3- reabsorption

Question 9

[RENAL]

What are the 2 methods of fixed H+ secretion?

Answer 9

1. Secretion via titratable acid

2. Secretion via NH4+

Question 10

[RENAL]

Factors that determine secretion of H+ as a titratable acid

Answer 10

1. Amount of buffer

2. The pK of the buffer

Question 11

[RENAL]

Factors that determine secretion of H+ as NH4+

Answer 11

1. The amount of NH3 produced

2. The pH of the urine

Question 12

[RENAL]

Describe the relationship between K+ and NH3 production

Answer 12

K+ inhibits NH3 production
Hyperkalemia -> Less NH3 production -> Less acid excretion
Hypokalemia -> More NH3 production -> More acid excretion

Question 13

[RENAL]

What is the serum anion gap? What is the normal value?Differentiate High and Normal Anion Gap

Answer 13

Serum anion gap reflects the amount of unmeasured anions (e.g. phosphate, citrate, sulfate, protein)

Normal value: 12 mEq/L

High Anion Gap - increase in unmeasured anions to compensate for lost HCO3-
Normal Anion gap - no increase in unmeasured anions to compensate for lost HCO3-. Cl- compensates instead.

Question 14

[RENAL]

Describe the relationship between H+ and Ca2+

Answer 14

H+ and Ca2+ compete in protein binding

More H+ -> Less Ca2+ binding -> More Free Ca2+
Less H+ -> More Ca2+ binding -> Less Free Ca2+

Question 15

[RENAL]
Describe the primary disturbance, compensation, correction of:
1. Metabolic Acidosis
2. Metabolic Alkalosis
3. Respiratory Acidosis
4. Respirator Alkalosis

Answer 15

Metabolic Acidosis - decrease in HCO3-, hyperventilation, correction via secretion of H+
1 mEq/L decrease = 1.3 mmHg decrease in pCO2

Metabolic Alkalosis - increase in HCO3-, hypoventilation, correction via increased excretion of HCO3-
1 mEq/L increase = 0.7 mmHg increase in pCO2

Respiratory Acidosis - increase in pCO2, compensation via increased HCO3- reabsorption, increased secretion of H+
1 mmHg increase = 0.1 increase (acute), 0.4 increase (chronic)

Respiratory Alkalosis - decrease in pCO2, compensation via decreased HCO3- reabsorption, decreased secretion of H+
1 mmHg decrease = 0.2 decrease (acute), 0.4 decrease (chronic)