Final answer:
Defensins are antimicrobial peptides that protect epithelial surfaces from pathogens by disrupting bacterial cell membranes.
Step-by-step explanation:
An antimicrobial peptide that protects epithelial surfaces from pathogens is defensin. Defensins are components of the immune system that protect the body by disrupting the cell membranes of bacteria, a critical function in the body's defense. While other substances mentioned, such as glycoproteins, proteoglycans, lysozyme, and sebum, play various roles in the protection and functioning of the body, it is the defensins that are specifically known for their antimicrobial properties, particularly on epithelial surfaces.