pH regulation

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pH regulation
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Blood pH

• pH measure of hydrogen ion concentration
• pH -log H
• Blood pH 7.35-7.45
• pH imbalances are quickly lethal ? body needs to
  compensate

• H intake
• - food
• - drink
• - metabolism (carbohydrate, protein, lipid)
• - breathing
• H output
• - urine

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Figure 19.23
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pH regulation

• Three lines of defense
• - Buffers
• - Respiration
• - Kidneys

• Buffer reactions are nearly instantaneous.
  However, they are limited to the amount of buffer
  available in the blood
• Respiration helps buffer the blood by shifting H
  into HCO3-. However, it can be limiting and take
  several minutes
• Kidneys are the only organ which can get rid of
  H. However, they can take several hours (time
  enough to be dead!!-? therefore, the presence of
  the other 2 lines of defense)

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pH regulation

• Three lines of defense
• - Buffers
• - Respiration
• - Kidneys

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First line of defense Buffers

• Buffers
• - protein buffer
• - bicarbonate buffer
• - phosphate buffer
• Only free H contributes to pH
• H can be shifted from a strong acid to a weaker
  one.

• Strong acid ? complete dissociation
• (100) HCl ? (100)H (100) Cl-
• Weak acid ?
• (100) H2CO3 ? (80) H2CO3
• (20) H
  (20) HCO3-

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pH regulation

• If strong acid intake
• H Cl- ( blood Na HCO3-) ?
• Na Cl- H HCO3-
• Less H is circulating into the blood - ?
  smaller shift toward acidosis

• If strong base intake
• Na OH- (blood H2 CO3) ? H2O Na HCO3-
• Less OH- is circulating in the blood ? smaller
  shift toward alkalosis

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Second line of defense breathing

• Three lines of defense
• - Buffers
• - Respiration
• - Kidneys

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• CO2 H2O ?? H2CO3 ?? H HCO3-
• CO2 retention
• ? blood H ? ? pH ? acidosis
• CO2 loss
• ? blood H ? pH ? ? alkalosis

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Figure 17.22
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Figure 19.24
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Third line of defense kidneys

• Three lines of defense
• - Buffers
• - Respiration
• - Kidneys

• Kidneys are the only organs able to eliminate H
  from the body ? slow process

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• H can be bound to HCO3- for transport to the
  bladder and eliminated
• H can be added to NH3 to make ammonia (NH4) and
  eliminated
• H can be eliminated directly by exchange with
  Na
• Urine is usually slightly acid. Its pH varies
  with food and drink intakes

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Clinical applications

• Acidosis Blood pHlt7.35

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Figure 19.28