Final answer:
The term for the structures that line cavities with openings to the outside of the body and function in protection, secretion, and absorption is 'mucous membranes'.
Step-by-step explanation:
The structures that line cavities with openings to the outside and function in protection, secretion, and absorption are commonly referred to as mucous membranes. These membranes are part of the larger category of epithelial membranes, which also include your skin.
Composed of epithelium attached to a layer of connective tissue, mucous membranes line various body cavities and tracts, including the digestive, respiratory, urinary, and reproductive systems. The mucosa, found as the innermost layer,
primarily consists of the epithelium capable of secreting digestive enzymes, mucus, and absorbing nutrients and water The presence of structures such as villi and microvilli in the epithelium greatly increases the surface area available for absorption.
Villi, for instance, are vascularized projections located within the mucosa that enhance nutrient uptake by increasing the epithelial surface area. Moreover, the epithelium of the small intestine, where these adaptations are most pronounced, is an excellent example of form matching function.
As it's involved in the critical task of nutrient absorption from digested food. In short, mucous membranes not only serve as a protective barrier but also are vital for the proper functioning of various organ systems through their roles in secretory and absorptive processes.