What substance neutralizes acidic chyme in the duodenum?

The neutralization of acidic chyme that enters the duodenum from the stomach is a critical process for proper digestion. The substance that primarily accomplishes this is bicarbonate (HCO3).

When the acidic chyme reaches the duodenum, the pancreas releases bicarbonate into the small intestine. Bicarbonate is alkaline in nature and serves to raise the pH level of the chyme, counteracting its acidity. This neutralization is essential because the enzymes that function in the small intestine, particularly those involved in carbohydrate, protein, and fat digestion, require a more neutral to slightly alkaline environment to be effective.

Bile, while it plays a crucial role in the emulsification of fats, does not specifically neutralize the acidity of chyme. Acetic acid is actually an acid rather than a neutralizing agent, and pepsin is an enzyme that works optimally in acidic conditions, specifically in the stomach, not the duodenum. Therefore, bicarbonate is the correct choice for neutralizing acidic chyme in the duodenum, allowing for optimal enzyme activity and further digestion.