Exam 2 Review:  Chapter 5:  Skin Coloration

melanin - Any of a group of naturally occurring insoluble dark (brown to black) pigments, found in the skin (brown to black) and hair (brown to black to red to orange), produced by specialized epithelial cells = melanocytes of the stratum germinativum and distributed to other epithelial cells;  production of the pigment is stimulated by exposure to uv light; the pigment is also found in the external layer of the retina, in the outer layer of the choroid, and elsewhere in the body; melanin generally serves to prevent light from penetrating to deeper tissues; this is especially important in the skin for reducing mutagenic uv light penetration to deeper tissues; the pattern of melanin deposition is regulated by heredity while the concentration of the pigment is regulated by a combination of heredity and environment (uv light exposure).

carotene - An orange-yellow to red crystalline fat-soluble pigment [C₄₀H₅₆] found in animal tissues and certain plants, such as carrots and squash; it exists in several isomeric forms and is converted to vitamin A in the liver.

hemoglobin - The iron-containing respiratory pigment in red blood cells of vertebrates, consisting of about 6 percent heme (lipid)and 94 percent globin (protein (2 alpha and 2 beta chains)); in arterial blood, it is always combined with oxygen, and is then called oxyhemoglobin; it functions primarily to transport oxygen from the lungs to the body tissues and is also a significant buffer of the blood.

freckles - Any small brownish to orange spot on the skin, often turning darker or increasing in number upon exposure to the sun, caused by an increase in melanin deposition.

albinism - Congenital absence of any melanin pigmentation or coloration in a person, due to an hereditary defect in an enzyme in the melanin synthesis pathway, resulting in pale skin, white hair and pink eyes.

vitiligo - A rare* acquired, possibly autoimmune, skin disease exhibiting a reduction in melanocytes and the resulting development of smooth, milk-white spots or patches of unpigmented skin (often surrounded by a heavily pigmented border) upon various parts of the body; hair in the affected areas is usually, but not always, white.  [* Vitiligo is the most common skin pigmentation disorder.]

pallor - The unnatural lack of color in the skin (as from bruising or sickness or emotional distress); generally the reduction in color is due to less red hemoglobin being routed through the subcutaneous capillary beds or there may be a systemic anemia.

cyanotic - A bluish discoloration of the skin and mucous membranes resulting from inadequate oxygenation of the blood.

jaundice - Yellowish discoloration of the whites of the eyes, skin, and mucous membranes (and of the urine) caused by the accumulation in these tissues of bilirubin (a lipid-soluble breakdown product of the heme groups in hemoglobin); it occurs as a symptom of various diseases, such as hemolytic disorders, hepatitis and other liver diseases, and with obstruction of the bile duct system. Also called icterus.

erythema - Redness of the skin caused by dilatation and congestion of the capillaries, often a sign of inflammation or infection.

List:

 7. three pigments that may contribute to normal skin color and their colors.

          melanin - brown to black
          carotene - yellow to orange
          hemoglobin - pink to red

          [bilirubin (in certain disease states, e.g., internal hemorrhage, liver disease, gall bladder & biliary tree obstructions) - yellow to amber]

 8. seven factors that influence the color of a person's skin.

          general - heredity, age, diet, general health, stress and lifestyle
          anatomical - depth of epidermis & dermis, degree of dermal vascularization, trauma and presence of scar tissue
          melanin - heredity, exposure to uv light radiation
          carotene - heredity, diet
          hemoglobin - dermal circulation, thermoregulation, emotional state, anemia, hemoglobin oxygenation status

[For additional information, read What Controls Variation in Human Skin Color?]