What substance does lipase primarily act upon in the digestive system?

Lipase is an enzyme that specifically breaks down fats (lipids) into smaller molecules called fatty acids and glycerol. In the digestive system, lipase is crucial for the emulsification and digestion of dietary fats, which are not soluble in water. This process is essential because fats need to be broken down into smaller pieces to be absorbed through the intestinal walls into the bloodstream. The presence of bile salts aids lipase's action by emulsifying fats, making them more accessible for enzymatic action.

The other substances listed—proteins, carbohydrates, and nucleic acids—are not the substrates that lipase acts upon. Proteins are broken down by proteases, carbohydrates by amylases, and nucleic acids by nucleases. Each enzyme in the digestive system has a specific substrate it targets, highlighting the specialized nature of digestive processes. Understanding these functions is vital for comprehending how the body assimilates nutrients from food.