Answer;
Mucus
Mucus is a viscous solution that lubricates and protects the gastrointestinal tract.
Step-by-step explanation;
-Mucus is a viscous colloid that contain inorganic salts, antiseptic enzymes , immunoglobulins, and glycoproteins such as lactoferrin and mucins, which are produced by goblet cells in the mucous membranes and submucosal glands.
-In the gastrointestinal tract, mucus is used as a lubricant for materials that must pass over membranes, e.g., food passing down the esophagus. A layer of mucus along the inner walls of the stomach is vital to protect the cell linings of that organ from the highly acidic environment within it.