There are numerous reasons that each of the four processes can occur (detailed in each article). Generally speaking, sources of acid gain include:
# Retention of carbon dioxide
# Production of nonvolatile acids from the metabolism of proteins and other organic molecules
# Loss of bicarbonate in feces or urine
# Intake of acids or acid precursors
Sources of acid loss include:
# Use of hydrogen ions in the metabolism of various organic anions
# Loss of acid in the vomitus or urine
# Gastric aspiration in hospital
# Severe diarrhea
# Carbon dioxide loss through hyperventilation