Buffer Systems in the Human Body: A Key Concept for the DAT

Maintaining pH balance is crucial for biological functions, and buffer systems play a key role in stabilizing pH changes in the body. On the DAT, understanding buffer systems will help you tackle questions in both the biology and chemistry sections. In this blog, we’ll explore the three primary buffer systems in the human body and their significance in maintaining homeostasis.

What is a Buffer System?

A buffer is a solution that resists changes in pH when acids or bases are added. It typically consists of a weak acid and its conjugate base or a weak base and its conjugate acid. The body uses buffer systems to maintain a stable pH, ensuring proper cellular and enzymatic function.

1. Bicarbonate Buffer System (HCO₃⁻/H₂CO₃)

Primary Function: Maintains blood pH (~7.4)

• The bicarbonate buffer system is the most important buffer in the extracellular fluid, especially in the blood.

• It regulates pH through the following equilibrium reaction:

  CO₂ + H₂O ⇌ H₂CO₃ ⇌ HCO₃⁻ + H⁺

• The lungs help remove excess CO₂, shifting the reaction left to reduce acidity.

• The kidneys regulate bicarbonate (HCO₃⁻) levels, excreting or reabsorbing it as needed.

• Clinical Relevance: Disruptions can lead to respiratory acidosis/alkalosis or metabolic acidosis/alkalosis, conditions often tested on the DAT.

2. Phosphate Buffer System (H₂PO₄⁻/HPO₄²⁻)

Primary Function: Regulates intracellular pH and renal (kidney) function

• The phosphate buffer system operates mainly inside cells and in the kidneys.

• The buffering reaction is:

  H₂PO₄⁻ ⇌ HPO₄²⁻ + H⁺

  It is especially important in urine, where it helps the kidneys excrete H⁺ ions to maintain blood pH.

3. Protein Buffer System (Hemoglobin & Albumin)

Primary Function: Regulates pH within cells and in the bloodstream

• Proteins act as buffers due to their ability to bind or release hydrogen ions (H⁺).

• Hemoglobin (Hb): Plays a major role in buffering blood pH by binding to H⁺ when CO₂ is high.

• Albumin: The most abundant plasma protein, helps buffer pH changes in the blood.

• Amino Acids: Contain both acidic and basic groups, allowing them to act as buffers.

DAT-Style Question Example

A patient has a condition that leads to increased CO₂ retention in the lungs. How will the bicarbonate buffer system respond?

A) Shift the reaction to the left, reducing H⁺ concentration
B) Shift the reaction to the right, increasing H⁺ concentration
C) No change in blood pH
D) The phosphate buffer system will compensate instead

Answer: B – Increased CO₂ shifts the reaction right, increasing H⁺ concentration and lowering pH (respiratory acidosis).

Master Buffer Systems with KOTC

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