What is the life span of a normal skin cell? (Answered by Manu Sharma)

Info source:
http://www.madsci.org/posts/archives/2000-09/969294613.Cb.r.html

(Answered by: Manu Sharma, Grad student, Laboratory Medicine and Pathobiology, The Hospital for Sick Children. Date: Sun Sep 17 16:21:13 2000. Area of science: Cell BiologyID: 966726597.Cb)

Skin or epidermis refers to a specific kind of epithelium- a continuous sheet of cells that separates the blood-supplied side of the tissue from the "outside" environment (which, for example, includes the cavity within esophagus/food-pipe or within trachea/wind-pipe).

Skin is the kind of epithelium that has evolved to protect us from the dry and pathogen-filled environment on the surface of the body.

It is a layer of epithelial cells that originate at the base and move toward the surface continuously, at a rate that replenishes the constantly shedding older cells from the surface.

The life-span of the skin cell therefore depends on how fast the surface cells are shed and how many layers thick the skin is over a particular part of the body.

Another interesting fact about the skin cells that determines their life-span is their "keratinization". Keratin is a protein found in hair, nails or skin.

This protein starts accumulating in a skin cell as it moves toward the surface through the layers. By the time this cell is shed from the surface, it is dead and full of keratin.

These layers of dead keratinized cells at the surface (called "squames") are flat (squamous), scaly and tough, protecting the underlying live layers.

The constantly dividing cells at the base of skin that make new ones of these Kamikaze skin cells are called basal cells or stem cells.

Although the stem/basal cells last a lifetime, a typical epidermal cell has a life span of about 2 to 4 weeks depending upon the part of the body.

You can read more about skin, other epithelia and all about cells, in "Molecular Biology of the Cell" by Alberts, Bray, Lewis, Raff, Roberts and Watson (yes the one who co-discovered the structure of DNA!), published by Garland Publishing, NY.

I have an older version, so the page numbers differ, but you can look up "epidermis", "dermis" or "epithelium" in the index. Other cell Biology texts at the undergraduate level also have similar chapters.