Integumentary
10-12
6-9
The Skin

     The skin has two layers: the epidermis and the dermis.  The epidermis is the upper layer of the skin.  It has up to five layers, called strata.  Under the epidermis is the dermis.  This layer connects the skin to the underlying tissue.  It is in the dermis that hair follicles and sweat glands reside.  Fingerprints are a result of dermal ridges which produce looped and whirled ridges on the epidermis.  This gives the fingers and toes extra gripping ability.

     Skin color is determined by three pigments: melanin, carotene, and hemoglobin.  However, only melanin is made in the skin.  Melanin can be gradated into many different shades.  It is this ability of Melanin that gives different races different skin coloration.  Exposure to sunlight can also cause a temporary change in the color of melanin.  Carotene has a yellow-orange color and is primarily found in the palms and the soles.  Hemoglobin gives fair-skinned people a pink hue to their skin due to the lack of melanin in the epidermis, which makes it almost transparent.

     Hair on other mammals serves them to keep them warm.  However, the sparse covering of hair on the human body serves other purposes.  It is able to sense insects on the skin before they are able to sting.  The hair on the head serves to control and prevent heat loss as well as guard against sunlight and physical trauma.   Hair is produced by hair follicles in the skin.  These follicles are heavily vascularized and are surrounded by nerve fibers.  Goose bumps occur when small muscles pull the follicles upright producing a bump on the surface of the skin.

     Sweat gland are distributed throughout the skin.  Their basic function is to cool the body.  This is accomplished by evaporation.  Evaporation of sweat off of the body dissipates body heat.

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