Final answer:
The first line of defense secreted by the liver that acts as a surfactant (emulsifier) is bile.
Step-by-step explanation:
The first line of defense secreted by the liver that acts as a surfactant (emulsifier) is bile.
Bile is a yellowish green liquid that is produced in the liver and composed of water, bile salts, bile pigments, phospholipids, electrolytes, cholesterol, and triglycerides. The two components critical to emulsification are bile salts and phospholipids, which break down large lipid globules into smaller ones. This process dramatically increases the surface area available for lipid-digesting enzyme activity.