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I recently heard a comedian asked to name his favorite part of a woman's body. "The skin," he said. "If she doesn't have skin, I'm not going to be seen with her." Fair enough!

In fact, our skin has many purposes. It has an obvious role in appearance: Healthy-looking skin can affect how good you look. It also serves as a cooling system (think sweat glands) and contributes to bone health (as UV light helps your skin to make vitamin D). And that's just the beginning.

Your skin is also a container. It protects your internal organs and structures from the outside world. And keeps everything where it belongs — inside.

The body has several other "containment systems." Think of them as "liners" that protect vital organs. Most people don't hear about these until they need to – when something goes wrong. In case that happens, you'll understand what your doctor is saying.

For example:

Pericarditis – Inflammation of the lining of the heart; common causes include viral infections, kidney failure and lupus.
Pleurisy (or pleuritis) – Inflammation of the lining of the lung; infection is the most common cause.
Meningitis – Inflammation of the lining of the brain; infection is the most common cause.
Peritonitis – Inflammation of the lining of the abdominal cavity; common causes include appendicitis or perforation of a part of the digestive tract (as with an ulcer or diverticulitis).

Other diseases that involve the body's linings include:

Gingivitis – Inflammation of the gingiva, the lining of the gums, due to infection. It can cause pain, swelling and tooth loss.
Conjunctivitis – Inflammation of the conjunctiva, the lining that covers the surface of the inner eyelids and eye.
Endometritis – Inflammation of the endometrium, the lining of the uterus (womb). This is usually due to infection and can be a serious condition, especially during pregnancy or childbirth.
Mucositis – Inflammation of the mucosa (or mucous membrane), the lining of many "inner" portions of the body. Areas with mucosa that are prone to inflammation or infection include the digestive tract (from mouth to anus), nose and vagina.

Our body's liners do more than just separate one part of the body from another. In the digestive tract, for example, the mucosa:

Prevents toxins from entering the bloodstream
Discourages "foreign proteins" (as in certain foods) to which we may be allergic from getting into the bloodstream
Provides a barrier and an immune defense that prevents infectious organisms from getting into the body
Produces substances the body needs, such as antibodies, digestive enzymes and acid
Absorbs nutrients such as water, vitamins and electrolytes

In my view, the body's containment systems and liners are parts of the body that are underappreciated. They are also a part of your doctor's lingo that may be hard to understand … until now. The next time your doctor mentions pleurisy or meningitis, you'll be ready.

Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.

Contain Yourself -- The Language of Your Body's Linings