MadSci Network: Anatomy

Re: Re: Why are the palms and soles of black people lighter in colour

Date: Mon Jul 21 15:34:03 2003
Posted By: Art Anderson,
Area of science: Anatomy
ID: 1058762076.An


This is an interesting question.

The palms of the hands and soles of the feet of white and black people are lighter because there are five layers of epidermis on the palms and soles but only four layers of epidermis everywhere else.

Most skin is 4 layers composed of 4 cell types - a 5th layer is found in areas of high friction

  1. Stratum Corneum: uppermost layer of dead, keratinized cells - continually sloughing off (dander) - many surface glycolipids for waterproofing

  2. Stratum Granulosum: granular in appearance due to keratin producing granules and glycolipid producing granules - cell membranes are thickening here - all is in response to decreased blood supply due to distance from capillaries

  3. Stratum Spinosum: 2 cell types here: young keratinocytes and Langerhan's cells - also find cellular projections of melanocytes - Langerhan's are 1st line of immune system and function as macrophages

  4. Stratum Basale: rapidly dividing keratinocytes under the influence of epidermal growth factor - can rapidly divide due to close junction with vascular dermis

    Melanocytes: branch to touch all keratinocytes - produce vesicles of melanin that are excised from cells and engulfed by keratinocytes - keratinocytes accumulate melanin as an inclusion on the upper side of the cell - protects nucleus from UV damage - different rates of degredation of melanin lead to differing degrees of "darkness" - different types of melanocytes make variant types of color.

    Merkel Cells: associated with nerve endings to sense touch

  5. Stratum Lucidum: specialized layer just below stratum corneum in palms of hand and soles of feet - extremely strong layer because of keratin- fibril complex

Only the Stratum Basale has pigment containing cells, all the other layers are colorless but contribute the color of protein, which is an orangy tan color. This additional layer of epidermis called the stratum lucidum which lies just below the stratum corneum provides additional screening of solar irradiation. This, plus the fact that you normally hold your hands and feet with the palms and soles facing down greatly prevents sunlight from darkening these sites. Look at anyone with a sun tan and you will notice that their palms and soles are also much lighter than the skin of the dorsal surfaces.

Here are two web pages with additional information about skin. http://www.terrebo tes5.html

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