Lecture 20: Renal Acid Base Regulation

Question 1

Describe the terminology for acids and bases

Answer 1

Acids:

• Compounds that release H+ ions.
• Strong acids: Dissociate completely
• Weak acids (conjugate acid): Do not dissociate completely, but dissociate into: Hydrogen ions (H+), and Conjugate base

Bases:
* Compounds that accept H+ ions.

Question 2

There are two types of acids produced by the body. Describe the volatile acid

Answer 2

Volatile Acid is excreted from the lungs

• Carbon dioxide
• Product of cellular aerobic metabolism
• CO2+ H2O ↔ H2CO3
• H2CO3 is a weak acid
• H2CO3 ↔ H++ HCO3−
• Carbonic anhydrase catalyzes the reversible reaction above.

Question 3

There are two types of acids in the body. Describe the nonvolatile acid

Answer 3

Nonvolatile acids (fixed acids):

• Excreted from kidneys
• Sulfuric acid (product of protein catabolism)
• Phosphoric acid (product of phospholipid catabolism)
• Ketoacids, lactic acid, salicylic acid

Question 4

Define pH

Answer 4

pH

• -log[H+]
• H2O ↔ H++ OH─
• Does not dissociate completely
• At equilibrium, [H+] = [OH─] = 10-7
• Therefore, pH = pOH= -log[H+] = 7.0
• pH of 0.1 M HCl= 1.0 (Strong acid)
• [H+] = 10-1
• The greater the hydrogen ion concentration, the lower the pH
• pH < 7 is acidic; pH > 7 is alkaline (basic)
• Arterial blood pH = 7.4
• Venous blood pH = 7.35

Question 5

Describe the Henderson-Hasselbach equation

Answer 5

• Dissociation of a weak acid (conjugate acid):
  HA ↔ H++ A-
• Ka is the equilibrium constant for the dissociation reaction.
  Ka = [H+][A─]/[HA]
  Ka = [H+][A─]/[HA] → Kax [HA] = [H+][A─]
  [H+] = Ka x [HA]/[A─] → 1/[H+] = 1/Kax [HA]/[A─]
  = -log [H+] = -log Ka -log ([HA]/[A─])

pH = pKa+ log ([A─]/[HA])

• See Slide 8

Question 6

Describe Major Systems Regulating [H+]

Answer 6

• Chemical acid-base buffer systems of the body fluids.
• Respiratory center
• Kidneys

Question 7

Describe buffers

Answer 7

• A buffer is a substance that can reversibly bind H+.
• A buffer consists of a weak acid (HA) = conjugate acid
• HA ↔ H++ A─
• Ka= [H+][A─]/[HA]
• Buffer systems:
• Bicarbonate buffer system
• Phosphate buffer system
• Proteins as buffers

Question 8

Incomplete

Answer 8

Resume at slide 13