Renal Function Acid-Base Regulation

Question 1

Normal levels for acid base balance

Answer 1

Normal pH: 7.35-7.45
Bicarbonate: 24
PCO2: 40

Question 2

Fundamental mechanisms to control pH

Answer 2

Buffering: ECF largest buffer is bicarbonate, ICF consists of bicarbonate P and histidine groups on proteins, mostbuffering in resp acid-base disorders in intracellular due to ease which CO2 enters and leaves cells
Respiratory: abnormal PCO2 called respiratory acidosis or alkalosis
Renal mechanism: nonvolatile acid or base concentration and thus abnormal bicarbonate, metabolic acidosis or alkalosis
Slowest control mechanisms, very capable of restoring pH to near normal by altering secretion of H and reabsorption of bicarbonate and new production of bicarbonate

Question 3

Net acid excretion

Answer 3

Steady state amount of nonvolatile acid produced and net acid excretion must be equal
⅔ of nonvolatile acid excretion is in the form of NH4+, about ⅓ as TA which is primarily P
Normal all bicarbonate reabsorbed
Ability to actively secrete bicarbonate into urine when necessary
Max acidity of urine is about pH 4-4.5

Question 4

Reabsorption of bicarbonate

Answer 4

Concentration of bicarbonate inside renal cells greater than ECF and negative intracellular charge results in net electrochemical gradient the favors efflux
Powers symporter 1Na/3HCO3 (NCB1), power reabsorption of Na
Antiporter with Cl
Production of NH4 from glutamine produces alphaKG from which 2 bicarbonate are formed and reabsorbed with Na, excretion of ammonium adds base to plasma
Increased bicarbonate reabsorption competes with Cl
Late DT and CCD final regulatory sites for excretion of acid/base

Question 5

Two types of cells capable of secreting acid

Answer 5

In CCD

1. Each H secreted, adds bicarbonate to blood, bicarbonate efflux is mainly by antiporter v Cl
2. Secretes bicarbonate when needed, not active often, signaled by elevated intracellular pH

Question 6

Henderson Hasselbach Equation

Answer 6

pH = 6.1 + log (HCO3/0.03 PCO2)

Inc bicarbonate, inc pH
Inc PCO2, dec pH

CO2 and water produce strong acid and weak base, high concentration of base but an acidic solution

Question 7

PAG and UAG

Answer 7

PAG = Na - Cl + HCO3

UAG = Na + K - Cl

Question 8

Expected compensated values

Answer 8

PCO2: 80. 60. 40. 20
HCO3: 27-29. 25-27. 23-25. 20-22

If amount of compensated not appropriate, suspect mixed disorder
1-3 hr for max compensation

Question 9

Plasma anion gap

Answer 9

Total positive and negative charge in ECF equal
Increase signals excessive metabolic acid in ECF
Normal value 12 +- 2
Used to determine cause of metabolic acidosis due to increased production or failure to excrete

Question 10

Urinary anion gap

Answer 10

Measure of amount of acid excreted in urine
Evaluation of hyperchloremic, normal anion gap acidosis
Urine normally has more anions than cations
If net excretion of acid, UAG is negative
Positive lots of NH4 in urine

Question 11

Four basic causes of metabolic acidosis

Answer 11

1. Excessive production of non volatile acids
2. Ingestion of acidic substances or those metabolized into acids
3. Renal failure to excrete acid or produce/reabsorbed bicarbonate
4. Loss of bicarbonate in GI system

Question 12

RTA

Answer 12

Hyperchloremic
Normal GFR
Normal anion gap acidosis

Question 13

Uremic acidosis

Answer 13

Low GFR

Elevated PAG

Question 14

Diarrhea

Answer 14

Loss of bicarbonate

Question 15

Acute or chronic renal failure

Answer 15

Acidosis
Increased anion gap
Reduced GFR
Bone being reabsorbed
Bicarbonate may seem moderately acidotic

Question 16

Acute tubular necrosis

Answer 16

Impaired excretion of acids
Bicarbonate 16-20
PAG 22-24

Question 17

Organic acid accumulation

Answer 17

Most common cause of acute metabolic acidosis

Large anion gap