Advanced Pathophysiology Lecture 1.6 Acid-Base Balance

What is the central physiologic challenge of acid-base balance?

Metabolism continuously produces acids and hydrogen ions, so the body must continuously buffer, eliminate, or compensate for acid production to maintain a narrow pH range.

Why does the body require continuous acid-base regulation rather than occasional correction?

Acid-producing processes occur continuously during normal metabolism, eating, physical activity, and cellular energy production. Acid-base control must therefore operate continuously.

What is the primary source of volatile acid?

Metabolism of carbohydrates and fats produces CO₂ and H₂O. These combine to form carbonic acid:

CO₂ + H₂O ⇌ H₂CO₃

Why is carbonic acid considered a volatile acid?

Because its CO₂ component can be eliminated through the lungs by exhalation.

What are fixed or nonvolatile acids?

All acids other than carbonic acid are described as fixed/nonvolatile acids because they cannot simply be exhaled and must be handled largely through the kidneys

What metabolic processes generate fixed acids?

• Incomplete carbohydrate metabolism → lactate

• Fat metabolism → ketones

• Protein metabolism → sulfate and phosphate

What does a chemical buffer do?

A buffer temporarily absorbs or binds an acid or base, limiting how dramatically pH changes when hydrogen ions are added or removed.

What protein-based buffers are emphasized?

• hemoglobin,

• other serum proteins.

What other buffering systems are mentioned?

• bicarbonate buffering,

• bone buffering.

Bone can absorb H⁺ and release calcium, which may contribute to bone loss during chronic renal disease.

What four major chemical buffer systems can be used to complete the objective?

• Bicarbonate/carbonic acid

• Protein buffers, including plasma proteins

• Hemoglobin

• Phosphate/bone buffering

How do the lungs regulate acid-base balance?

Chemoreceptors in the:

• medulla,

• carotid bodies,

• aortic arch

alter the rate and depth of respiration to control CO₂.

What happens to acid-base balance during hyperventilation versus hypoventilation?

• Hyperventilation: more CO₂ lost → carbonic acid decreases → pH rises.

• Hypoventilation: CO₂ retained → carbonic acid increases → pH falls.

Respiratory compensation occurs over minutes to hours.

How do the kidneys regulate acid-base balance?

The kidneys adjust:

• hydrogen-ion excretion,

• bicarbonate handling,

• excretion/retention of fixed acid.

How quickly do the kidneys respond compared with the lungs?

Renal changes may begin within approximately 2–6 hours, but full equilibrium takes around 2–3 days.

Why can metabolic acid-base disorders receive compensatory correction faster than respiratory disorders?

A metabolic disorder can be compensated by the lungs, which alter ventilation within minutes to hours.

A respiratory disorder requires substantial renal compensation, which begins over hours but may require 2–3 days to reach equilibrium.