What is the thick, sticky fluid secreted by mucous membranes called?

Mucus is the thick, sticky fluid secreted by mucous membranes, which are found lining various cavities in the body and covering the surfaces of internal organs. This viscous substance plays a critical role in the body’s defense mechanisms. It serves to lubricate and protect these membranes, trapping pathogens, dirt, and other particles that could cause harm. Mucus also helps to keep tissues moist and can be involved in various physiological functions, such as digestion and respiratory processes.

The other options do not accurately describe this specific fluid. Serum refers to the clear fluid that remains after blood has clotted and does not have the thick consistency or protective function of mucus. Secretions is a more general term that encompasses various fluids produced by glands, but it does not specifically refer to the sticky fluid of the mucous membranes. Saliva, while it is a fluid secreted from salivary glands, primarily contains enzymes for digestion and does not serve the unique protective and lubricating functions of mucus found in mucous membranes. Thus, mucus is clearly distinguished as the correct answer in this context.