By measuring telomeres, some scientists believe they can determine biological age, which doesn't always equal chronological age. That means some people may be biologically older or younger than their age, said Jerry Shay, professor and vice chairman of cell biology at UT Southwestern Medical Center in Dallas.
It is of ectodermal origin and is continuous with the skin at various body openings such as the eyes, ears, nose and mouth, the urethral opening and the anus. Some mucous membranes secrete mucus, a thick protective fluid. The function of the membrane is to stop pathogens and dirt from entering the body and to prevent bodily tissues from becoming dehydrated.
Although some mucins are membrane-bound due to the presence of a hydrophobic membrane-spanning domain that favors retention in the plasma membrane, most mucins are secreted onto mucosal surfaces or secreted to become a component of saliva.