Final answer:
A labial frenulum is a narrow fold of mucous membrane that connects the inner surface of the lips to the gums, serving as an example of the important functions that mucous membranes serve throughout the body.
Step-by-step explanation:
A labial frenulum is a narrow fold of mucous membrane passing from a more fixed to a movable part. This structure can be found in the mouth, where it connects the inner surface of the lips to the gums. The mucous membrane itself is a type of epithelial tissue that lines inner body surfaces and openings and is responsible for the production of mucus, which serves as a protective layer.
The importance of mucous membranes extends to various parts of the body, such as the respiratory and gastrointestinal tracts, where they help in absorption and protection. For example, in the gastrointestinal tract, structures like the circular folds and villi aid in the absorption of nutrients.