Final answer:
Mucous membranes secrete mucus containing antimicrobial agents to protect the body against pathogens. The mucus is a thick fluid that traps pathogens and is moved by cilia on the membranes toward body openings to be expelled. Balance of electrolytes is crucial for maintaining mucus consistency for effective movement and expulsion.
Step-by-step explanation:
Mucosal surfaces are lined with mucous membranes, which are covered in mucus, a thick and viscous fluid. This mucus is secreted by epithelial cells, including goblet cells, that make up the mucous membranes. These secretions typically contain antimicrobial agents to help fend off pathogens, as well as substances for lubrication of the surfaces. Cilia, small hair-like structures, are often present on these membranes and work to sweep the mucus along with any trapped pathogens toward body openings where they can be expelled from the body.
In the respiratory system, the mucus traps dust, bacteria, and other debris. Normal functioning involves the balance of electrolytes, such as chloride ions (Cl-) and sodium ions (Na+), which maintain a watery consistency of mucus by creating an osmotic gradient that attracts water. This helps the cilia to move the mucus effectively. In disorders like cystic fibrosis, the CFTR channel is absent, which disrupts Cl- transport, leading to thick and sticky mucus that cilia cannot adequately move, causing blockages and increased risk of infections.
Furthermore, in the gastrointestinal tract, mucous membranes secrete alkaline mucus as a protective coating against the harsh acidic environment, with gastric glands contributing to the secretion of gastric juice. Overall, the mucus on mucosal surfaces serves as an important defense mechanism of the body.