Final answer:
Simple columnar epithelial cells form the single layer of the surface of mucous membranes, often appearing as pseudostratified due to the nuclei arrangement. These cells play a role in protecting organs by moving mucous and using cilia or microvilli depending on their location.
Step-by-step explanation:
The single layer of tall, thin cells that compose the surface of mucous membranes are known as simple columnar epithelial cells. They appear as pseudostratified columnar epithelia due to the arrangement of their nuclei at various levels, which gives the appearance of multiple layers. Notably, these cells can have cilia or microvilli on their apical surface depending on their location in the body. For instance, in the respiratory tract, these ciliated columnar cells aid in moving mucous and trapped particles out, while goblet cells found among them secrete mucus that traps irritants to protect the lungs.
In contrast, in the small intestine, the microvilli atop the columnar epithelial cells enhance the surface area for nutrient absorption.
Different epithelial cells are adapted for specific roles in the body, with mucous membranes lining various organs based on whether the need is for protection, secretion, absorption, or excretion.