photo.jpg

## Thick Skin and Thin Skin The stratified squamous epithelium of the epidermis varies in thickness, depending upon the region of the body in which it is located. ### Thick Skin Thick skin contains all five epidermal strata and covers the palms of the hands and the soles of the feet. ### Thin S...

## Thick Skin and Thin Skin The stratified squamous epithelium of the epidermis varies in thickness, depending upon the region of the body in which it is located. ### Thick Skin Thick skin contains all five epidermal strata and covers the palms of the hands and the soles of the feet. ### Thin Skin Thin skin covers most body surfaces; it contains only four epidermal strata and lacks a stratum lucidum. ## What Do You Think? Why do you think thick skin lacks hair follicles and sebaceous glands? Think about where thick skin is located and how that may interfere with the function of skin in that area. ## Skin Color Normal skin color results from a combination of the colors of hemoglobin, melanin, and carotene. ### Hemoglobin Hemoglobin (hē-mō-glō'bin; haima = blood) is an oxygen-binding protein present in red blood cells. It exhibits a bright red color upon binding oxygen, thus giving blood vessels in the dermis a reddish tint that is seen most easily in lightly pigmented individuals. If the blood vessels in the superficial layers vasodilate (i.e., the blood vessel diameter increases), such as during physical exertion, then the red tones are much more visible. ### Melanin Melanin is a pigment produced and stored in melanocytes. Two types of melanin are present in the skin, eumelanin and pheomelanin. Eumelanin produces shades of brown and black, whereas pheomelanin produces lighter shades of tan, yellow, and red. Recall that melanin is transferred in melanosomes from melanocytes to keratinocytes in the stratum basale. Because keratinocytes are displaced toward the stratum corneum, melanocyte activity affects the color of the entire epidermis. The physical appearance of the skin due to melanin is influenced by both heredity and exposure of the skin to UV light. All people have about the same number of melanocytes. However, melanocyte activity, the types of melanin present in the epidermis, and the color of the melanin produced by these cells vary among individuals and ethnicities, resulting in different skin color tones. Darker-skinned individuals have melanocytes that produce relatively more and darker melanin than lighter-skinned individuals. Further, these more active melanocytes tend to package melanin into cells in the more superficial epidermal layers, such as the stratum granulosum. This difference in skin color is temporarily altered when our skin is exposed to UV light, which stimulates melanocytes to make more melanin. ### Carotene Carotene (kar'ō-ten) is a yellow-orange pigment that is acquired from various yellow-orange vegetables, such as carrots, corn, and squashes. Normally, it accumulates inside keratinocytes of the stratum corneum and in the subcutaneous fat. There are several forms of carotene (e.g., alpha-carotene, beta-carotene), but beta-carotene is the most common type found in plants and is the primary source of provitamin A (i.e., it can be converted into vitamin A). Beta-carotene is converted into vitamin A in the liver. This vitamin plays an important role in vision. Vitamin A has also been thought to reduce potentially dangerous molecules called free radicals. ## Production of Melanin by Melanocytes Melanin gives a yellow to tan to brown or black color to the skin. * **Melanosomes in melanocytes transport the melanin pigment to the keratinocytes, where the pigment surrounds the nucleus.** * **Melanin is incorporated into the keratinocytes primarily of the stratum basale.**