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pigment

pigment

1. Any coloring matter, as that of the red blood cells, hair, iris, etc., or the stains used in histologic or bacteriologic work, or that in paints. 2. A medicinal preparation for external use, applied to the skin like paint. [L. pigmentum, paint]
bile p.'s coloring matter in the bile derived from porphyrins by rupture of a methane bridge; e.g., bilirubin, biliverdin.
chymotropic p. a p. dissolved in the vacuole of a plant cell. [G. chymos, juice, + trope, turning, inclination, + -ic]
formalin p. a p. formed when acid aqueous solutions of formaldehyde act on blood-rich tissues; characterized by rotation of the plane of polarized light, withstanding extraction in aqueous and lipid solvents, being bleached in acids and hydrogen peroxide; not formed when tissue is fixed with formaldehyde buffered to pH levels above 6.
hematogenous p. a p. derived from the hemoglobin of the red blood cells.
hepatogenous p. bile p. derived from the destruction of hemoglobin in the liver.
malarial p. a dark brown, granular p. which rotates the plane of polarized light and has other properties similar to formalin p.; occurs in parasites, such as Plasmodium malariae, around brain capillaries, and in fixed macrophages of spleen, liver, bone marrow, and lymph nodes. See malarial pigment stain.
melanotic p. melanin
natural p. a naturally occurring colored compound; absorbs light in the visible range of the electromagnetic spectrum. Cf. structural color. biochrome;
respiratory p.'s the oxygen-carrying (colored) substances in blood and tissues (hemoglobin, myoglobin, hemocyanin, etc.).
visual p.'s the photopigments in the retinal cones and rods that absorb light and initiate the visual process.
wear-and-tear p. lipofuscin that accumulates in aging or atrophic cells as a residue of lysosomal digestion.

 

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