2.16 - Metabolic Acid Base

Question 1

What is the normal range for blood pH?

Answer 1

7.38-7.42

Question 2

What changes occur in the kidney during acidosis?

Answer 2

Secrete H+ by primary and secondary active transport

Buffer H+ with ammonia and phosphate (H2PO4– + H+ <–> H2PO4-)

Make new HCO3- from CO2 and H2O

Question 3

What is titratable acid?

Answer 3

Urinary buffers are collectively called titratable acid. The primary urinary buffer is phosphate

Question 4

Describe the reabsorption of filtered HCO3-

Answer 4

Mediated by H+ secretion

Primarily regulated by the H+ gradient

Activity and expression of key H+ and HCO3- transporters is also regulated In collecting duct, acidosis increases H+-ATPase expression. In proximal tubule, acidosis increases Na+/H+ antiporter and Na+/ 3HCO3- expression and activity

Question 5

Describe the need for formation of new HCO3-

Answer 5

For acid-base balance to be maintain, the kidneys must replenish any lost HCO3-

Two mechanisms are involved in the renal generation of new HCO3-: Some of the HCO3- is produced during titration of urinary buffers. This is not regulated by the body’s requirement to maintain a normal pH.

Synthesis of NH4+ by the kidney produces new HCO3-. This process is regulated by the body’s requirement to maintain a normal pH

Question 6

Describe Urine Anion Gap

Answer 6

Cation charge = anion charge

[Na+] + [K+] + [NH4+] = [Cl-] + [HCO3-]
[NH4+]: measurement not routinely available [HCO3-]: Virtuallynone present in urine

Therefore: [Na+] + [K+] + gap = [Cl-]
UAG=[Na+]+[K+]–[Cl-]

UAG = rough index of [NH4+]

Question 7

Describe Plasma Anion Gap

Answer 7

Plasma also maintains macroscopic electroneutrality

[Na+] + [other+] = [Cl-] + [HCO3-] + [other-]

Na+ is a major plasma cation, Cl- and HCO3- are major plasma anions

[Na+] ~= [Cl-] + [HCO3-]

Anion gap = [Na+] – ([Cl-] + [HCO3-])