Chemical Buffer Systems AND. Respiratory Regulation of Acid-Base Balance

Chemical buffer

A system that resists changes in pH by binding or releasing H⁺.

How does a buffer respond to added acid

Its base component binds some of the added H⁺.

How does a buffer respond to added base

Its acid component can release H⁺ to oppose the pH increase.

Main extracellular buffer system

The bicarbonate–carbonic acid system.

Bicarbonate ion

HCO₃⁻; a base that can accept H⁺.

Carbonic acid

H₂CO₃; a weak acid that can release H⁺.

Bicarbonate buffer reaction

H⁺ + HCO₃⁻ ⇌ H₂CO₃ ⇌ CO₂ + H₂O.

What happens when H⁺ increases

Bicarbonate binds H⁺, forming carbonic acid, which can be converted to CO₂ and water.

What happens when H⁺ decreases

Carbonic acid can dissociate to release H⁺.

Why is the bicarbonate buffer system effective

Its components are regulated by both the lungs and kidneys.

Protein buffers

Proteins that bind or release H⁺ through ionizable groups.

Haemoglobin buffer

Haemoglobin in red blood cells helps bind H⁺ associated with CO₂ transport.

Phosphate buffer system

A buffer system involving phosphate species that can bind or release H⁺.

Where is the phosphate buffer especially important

Inside cells and in kidney tubular fluid.

Buffer limitation

Buffers resist pH changes but do not independently eliminate the underlying acid or base load.

How does CO₂ affect pH

CO₂ combines with water to form carbonic acid, which can release H⁺.

CO₂ and carbonic acid relationship

Increased CO₂ tends to increase H⁺ and lower pH.

Effect of increased ventilation on CO₂

More CO₂ is exhaled, reducing blood CO₂.

Effect of increased ventilation on pH

It tends to raise pH by reducing CO₂.

Effect of decreased ventilation on CO₂

CO₂ is retained, increasing blood CO₂.

Effect of decreased ventilation on pH

It tends to lower pH.

Respiratory compensation for acidosis

Increasing ventilation can lower CO₂ and help raise pH.

Respiratory compensation for alkalosis

Decreasing ventilation can retain CO₂ and help lower pH.

Why is respiratory compensation limited

The lungs adjust CO₂ but cannot directly correct every cause of acid-base disturbance.

What does CO₂ represent in the bicarbonate buffer system

The respiratory-regulated component.