Think of epithelial tissue like the skin on a fruit or the lining inside a pipe, which protects or encloses. Blood is more like a delivery truck service driving inside those pipes; it connects various body systems rather than forming the walls of the pipes themselves.

Epithelial tissues are characterized by cells closely packed together with little intercellular matrix, forming continuous sheets. In contrast, connective tissues, such as blood, are characterized by cells separated by an abundant extracellular matrix. Blood's primary role is transport, facilitated by its fluid state, which is distinct from the protective and secretory functions of epithelial tissues.

Always remember the 'Four Basic Tissue Types': Epithelial, Connective, Muscular, and Nervous. Identifying which category a structure belongs to is a frequent question in RRB biology exams.