Lecture 32 -- acid base balance

what does our survival depend on?

• v tight regulation between acid and bases in the blood

what is acid and bases in blood measured with? what’s the equation?

• pH scale

  • pH of 7.37 -7.42 = normal

  • pH of 6.8 - 8.-00 = survival limits

• pH = -log[H+]

what do buffer systems do?

• help minimize the change in free H+ concentration (=minimize pH changes)

what is the main sources of H+ production in the body?

• constantly produced by normal metabolism

• two principle sources:

  • volatile acid = ~12,000-20,000 mmolday of CO2 (carbonic acid H2CO3)

    • byproduct of oxidative metabolism

    • lungs eliminate CO2

  • fixed (non-volatile) acid: ~50 mmol/day of inorganic and organic acid

    • cannot be eliminated by lungs

what are the 3 lines of defense against fixed acid-induced acidification of body fluids?

1. physiochemical buffering

   1. seconds-min

2. respiratory compensation (CO2 elimination)

   1. min-hour

3. renal compensation (H+ excretion; generation of HCO3)

   1. hrs-days

what is physiochemical buffering? major systems?

• fastest line of defense against H+ accumulation

• 3 major buffering systems in body fluid:

  • proteins

  • prosphate

  • bicarbonate/carbonic acid

    • most plentiful buffer in the body

what is respiratory compensation?

• regulates blood levels of carbonic acid (H2CO3)

• CO2 will readily form carbonic acid in the blood through reaction with water

  • high CO2 in blood = more H2CO3

  • more H2CO3 = lower blood pH (acidic)

what is renal compensation?

• the kidneys control levels of bicarbonate (HCO3-) in the blood

• nephron NOT permeable to HCO3-

how do you get around the fact the nephron is not permeable to bicarbonate?

• through indirect reabsorption of bicarbonate

• CA = carbonic anhydrase