Medical Education Without Limits!

Buffering as a Mode of Acid Base Balance

A buffer is a substance that can accept/release H+ ions to maintain the pH of a solution constant.

  • The human body has many major buffer systems which
  1. Provide a huge buffering capacity
  2. Provide immediate effect.
  • The major buffer systems in the body are
  1. The interstitial fluid (bicarbonate, phosphates and proteins)
  2. Blood (bicarbonate, phosphates, hemoglobin and plasma proteins)
  3. Intracellular fluids (phosphates and proteins)
  4. Urine (phosphates and ammonia)
  5. The skeletal system (calcium carbonate)
  • Total buffering capacity of blood

Buffering capacity %







Haemoglobin (RBC)



  • Bicarbonates are the most important buffers in the ECF, responsible for 80% of external buffering. But acid base disorders in the respiratory system cannot be buggered by bicarbonate due to very low concentrations.

pK (HCO3) = 6.1

  • Phosphate buffers are active in the intracellular environment and in urine. Sir to low concentrations, they are not very dominant in the ECF. Since phosphates have three different states, they can function under three different ranges

pK (phosphates) = 2, 6.8, 12

  • Haemoglobin (present as 150g/l) and plasma proteins (present as 70g/l) are important buffers in blood. Hb is 6 times more important than plasma proteins because Hb
  1. Has double the capacity of carbon dioxide storage
  2. Has three times more Justine per molecule

pK (plasma proteins & Hb) = 6.5

{Haemoglobin is a better buffer than oxyhaemoglobin – Explained by Haldane Effect}

  • Isohydric Principle – all buffer systems participating in acid base balance are in equity with each other.

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Categorised in: Biochemistry, Medicine, Physiology

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