Metabolic acidosis is described as a primary deficiency of which substance?

1. Acidosis means a blood pH below 7.35, however it arose. 2. The metabolic form arises when there is too little bicarbonate in the blood. 3. That is why it is named a primary bicarbonate deficiency. 4. A primary carbonic acid excess would instead be respiratory acidosis. 5. Its commonest cause is organic acids or excess ketones in the blood. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 26 "Fluid, Electrolyte, and Acid-Base Balance", section Metabolic Acidosis: Primary Bicarbonate Deficiency_