The Skin as Our Integument Help
Introduction to The Skin as Our Integument
“How is the human body like a peach?” In reply to this odd question, you might comically retort, “Well, we’re just a bunch of fruits!” But more seriously, both a peach and the human body are surrounded by an integument (in- TEG -you-ment) – a thin “covering.” And lying deep to this integument is a much thicker layer of flesh. Hence, it is the integument or “skin” (derm) that encloses and protects the flesh.
And the skin or integument of both the peach and the human body has an outermost layer, the epidermis. You might remember from our study of plants (Chapter 9) that the epidermis is literally “(something) present upon the skin,” and that in ferns and seedbearing plants (such as peach trees), the epidermis is an extremely thin layer of outer protective cells. But from here, the similarity between peach integument and human integument begins to fade (Figure 13.1).
Keratinized Epithelial Strata and Skin Coloration By Melanin
Keratinized Epithelial Strata
One key difference between the epidermis of humans and most other animals, from those of plants, is the presence of keratin. This “horn substance” is found in the epidermis and hair and nails of humans, as well as in the claws and horns of various other animals. Since keratin is essentially waterproof, so is human skin. Our epidermis consists of a multiple series of thin, overlapping strata ( STRAT -uh) of keratinized epithelial cells. When viewed under a light microscope, this highly orderly arrangement gives the epidermis the appearance of a collection of thin “layers or bed covers” (strat), heaped one upon the other over a bed.
The outer surface stratum (STRAT - um) is really not living, at all! Rather, it consists of a series of stacked squamae (SKWAY - me) – dead, keratinstuffed “scales” (squam). This means that you and I face the world with dead scales (squamae) showing at our body surface! But this has the definite advantage of protecting us from dirt, fungi, and bacteria, which cannot easily penetrate the multiple layers of lifeless squamae.
Skin Coloration By Melanin
In addition to containing keratin, the epithelial cells in our epidermis are also rich in melanin ( MEL -uh-nin) or “black” ( melan ) “substance” (- in ). Melanin is a brownish-black pigment produced by melanocytes ( MEL -uh-nuh- sights ). These “black cells” are large, octopus-shaped cells with several long arms of cytoplasm. After they produce the melanin granules, the melanocytes appear to penetrate the membranes of adjacent cells, and inject some of their melanin granules into them. This results in a darkening of the epidermis. Melanin’s chief function is absorption of ultraviolet ( ul -truh- VEYE -uh-lit) rays that strike the surface of the skin. These ultraviolet (UV) rays are invisible rays whose wavelengths lie “beyond” ( ultra -) those of X-rays, but below those of visible violet light. The benefits are dual: reduction in the risk of suffering skin cancer (due to mutation of skin cell DNA by UV light), and reduction in skin wrinkling.
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