First of a two-part column
I am a board certified dermatologist, and dermatology is the study of the skin, hair and nails. These three are often call the integument from the Latin word integumentum, which means “covering.” The integument plays an important role in the overall health, protection and well-being of the body.
The skin plays a vital role in our good health. This will be a two-part series. Next week we will discuss some of the fascinating things skin does for us. This week we will discuss the structure of skin and its three layers.
The thickness of skin on the body varies from super thin on the eyelids to super thick as on the palms and soles. The skin is made of three layers: the top epidermis; the middle layer, dermis; and the bottom layer, adipose/fat.
The waterproof epidermis is the protective outer layer of our skin. It contains many cells, including melanocytes. Melanocytes make the pigment melanin, which gives skin its color and, by absorbing sunlight, protects the body from the sun’s harmful ultraviolet rays. Only about two percent of the cells in the skin are melanocytes, but they have long arms, like an octopus, that deliver the melanin to the main skin cells called keratinocytes.
The epidermis is replaced on a regular basis by the daily shedding of millions of older skin cells. As newer skin cells rise up in the skin, they replace the older cells. This is a constant and never-ending process.
Sometimes the skin cells grow extremely fast and the older, upper cells can’t get replaced fast enough, so they pile up and form thick areas of skin. This is what happens when someone has psoriasis. The epidermis has no blood vessels but receives nutrients from the middle layer of skin below, known as the dermis.
Just beneath the epidermis is the dermis, a tough layer of skin that makes up the majority of what we think of as “skin.” The dermis is remarkable because it give the skin both strength and softness.
The dermis is not shed like the epidermis. The dermis stays pretty much the same throughout life. The dermis contains the strength and support proteins of collagen and elastin. The dermis also contains blood vessels, nerves, hair and oil and sweat glands.
The delicate sensory nerves can detect everything from the light touch of a kiss to pressure, vibration, and the sting of a needle. Nerve endings in the dermis can also detect both heat and cold. As a sense organ, it keeps the body informed about what is going on in the world around it.
The hypodermis (the subcutaneous adipose/fat layer)
The bottom layer of the skin, the subcutaneous adipose/fat layer, contains blood vessels and nerves that originate in the dermis and get bigger and then go to the rest of the body. The adipose tissue (fat) helps to regulate body temperature, keeping the body from getting too hot or too cold. It also plays a vital role in attaching skin to muscle and bones via connective tissue.
Finally, the adipose layer stores fat for long-term energy reserves and protects the muscles and skeleton from falls and bump injuries.
The skin is much more than just a protective covering. Next week we will talk about the ways skin keeps us healthy and the ways we can best take care of our skin.
Charles E. Crutchfield III, MD is a board certified dermatologist and Clinical Professor of Dermatology at the University of Minnesota Medical School. He also has a private practice in Eagan, MN. He has been selected as one of the top 10 dermatologists in the U.S. by Black Enterprise magazine and one of the top 21 African American physicians in the U.S. by the Atlanta Post. Dr. Crutchfield is an active member of the Minnesota Association of Black Physicians, MABP.org.