Degenerative disorders, including arthritis, Parkinson's disease, and Alzheimer's disease, involve the progressive breakdown of tissues and loss of function of parts of the body. The incidence of these problems increases with age, and, in at least some cases, progression can be slowed by good health habits. There are many ways to prevent these diseases. The skin and mucous membranes form the body's first line of defense against disease. Most microscopic pathogens, or microbes, cannot pass through unbroken skin, although they can easily enter through cuts and other wounds.
Mucous membranes protect internal organs that are connected with the outside of the body.
These membranes, which line the respiratory, digestive, urinary, and reproductive tracts, secrete mucus, which traps microbes. The mucus may then be expelled from the body, perhaps in a cough or sneeze or in feces. If the mucus is swallowed, digestive juices kill the microbes. Small hairlike projections on the lining of the nose, throat, and bronchial tubes work in conjunction with mucus to trap and remove foreign substances. In the ears, tiny hairs plus a sticky wax defend against the entry of germs.