Acid-Base Basics AND Sources of Hydrogen Ions

Acid-base balance

Precise regulation of free hydrogen-ion concentration in body fluids.

Acid

A substance that releases H⁺ in solution.

Base

A substance that accepts or binds free H⁺.

Strong acid

An acid that dissociates extensively in water.

Weak acid

An acid that dissociates only partially in water.

Hydrochloric acid (HCl)

A strong acid that dissociates extensively in water.

Carbonic acid (H₂CO₃)

A weak acid that only partially dissociates in water.

Dissociation constant (K)

A value describing the extent to which an acid dissociates.

Neutral pH

A pH of 7.0 for pure water under standard conditions.

Acidic solution

A solution with pH below 7.0.

Basic or alkaline solution

A solution with pH above 7.0.

Average blood pH

Approximately 7.40.

Arterial blood pH in the slides

Approximately 7.45.

Venous blood pH in the slides

Approximately 7.35, partly because venous blood contains more CO₂.

Acidemia

Blood plasma pH below 7.35.

Alkalemia

Blood plasma pH above 7.45.

Acidosis

A process that tends to decrease body-fluid pH.

Alkalosis

A process that tends to increase body-fluid pH.

Why is blood pH tightly regulated

Many proteins, enzymes, and cellular processes depend on a narrow pH range.

Main sources of H⁺

Metabolism and acids entering or being produced within the body.

Why must H⁺ be regulated

Excess H⁺ lowers pH, while reduced H⁺ raises pH.

Three lines of acid-base defence

Chemical buffers, respiratory regulation, and renal regulation.

First line of defence

Chemical buffer systems that rapidly bind or release H⁺.

Second line of defence

The respiratory system, which changes CO₂ removal.

Third line of defence

The kidneys, which regulate H⁺ excretion and bicarbonate handling.

Which defence acts fastest

Chemical buffers act almost immediately.

How does the respiratory system regulate pH

By changing ventilation to alter CO₂ levels.

How do the kidneys regulate pH

By secreting H⁺, excreting acid in urine, and conserving or generating bicarbonate.

Why are kidneys considered powerful regulators

They can provide extensive compensation and restore pH close to normal.

How quickly do renal acid-base responses occur

They require hours to days.