Acid-Base Regulation and Buffer Systems

Study Notes

Precise regulation of hydrogen ion (H+) concentration is crucial for nearly all enzyme functions in the body
Extracellular fluid H⁺ concentration is normally kept low
Normal variation is minimal compared to other ions like sodium
Acids release hydrogen ions; bases accept hydrogen ions
Buffering systems (e.g., bicarbonate, phosphate, proteins) resist changes in H⁺ concentration in the body fluids.

The most significant extracellular buffer is the bicarbonate system
It involves carbonic acid (H₂CO₃), and bicarbonate (HCO₃⁻)
CO₂ combines with water to form carbonic acid
Carbonic acid dissociates to form H⁺ and HCO₃⁻
The buffer system resists pH changes by absorbing excess H⁺ or releasing H⁺, depending on the situation.
The reverse reaction occurs in the lungs and kidneys to regulate the removal and addition of bicarbonate (HCO₃⁻).

Phosphate buffers play a key role in renal tubular fluid and intracellular fluids but less significant in extracellular fluid.
It involves H₂PO₄⁻ and HPO₄²⁻ ions
These ions can bind or release H⁺ depending on the direction of change in fluid pH.
The concentration of phosphate is higher in intracellular fluid compared to extracellular fluid, making it a more effective buffer within cells.
High phosphate concentration in renal tubules allows it to be a valuable buffer in these regions.

Proteins are crucial intracellular buffers due to their abundant presence.
Proteins can bind or release H⁺ depending on body fluid pH.
Their buffering capacity is affected in response to changes in H⁺ concentrations.

Ventilation rate impacts the concentration of carbon dioxide (CO₂) in the body.
Increased ventilation removes CO₂ which reduces H⁺ concentration and raises blood pH.
Decreasing ventilation increases CO₂ which increases H⁺ concentration and lowers blood pH.

Kidneys regulate acid-base balance by excreting acidic or basic urine.
Acid excretion lowers the concentration of H⁺ in the blood
Base excretion removes HCO₃⁻ , thus increasing H⁺ concentration
Maintaining acid/base balance requires an interplay of all three buffering systems (pulmonary, renal, and chemical): for instance, high CO₂ leads to high H⁺. pH decreases in response, thereby increasing respiration rate.
Ammonia buffer is a major component of renal acid-base regulation.
Glutamine metabolism is a primary source of ammonia production. Ammonia combines with hydrogen to form ammonium, which is excreted and results in formation of new bicarbonate for the blood.

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