- 1. Any of a group of chemically diverse proteins that appears microscopically homogeneous, but is composed of linear nonbranching aggregated fibrils arranged in sheets when seen under the electron microscope; it stains dark brown with iodine, produces a characteristic green birefringence in polarized light after staining with Congo red, is metachromatic with either methyl violet (pink-red) or crystal violet (purple-red), and fluoresces yellow after thioflavine T staining; a. occurs characteristically as pathologic extracellular deposits (amyloidosis), especially in association with reticuloendothelial tissue; the chemical nature of the proteinaceous fibrils is dependent upon the underlying disease process. 2. Resembling or containing starch. [amylo- + G. eidos, resemblance]
* * *am·y·loid 'am-ə-.lȯid n1) a nonnitrogenous starchy food2) a waxy translucent substance consisting primarily of protein that is deposited in some animal organs and tissue under abnormal conditions (as in Alzheimer's disease) see BETA-AMYLOIDamyloid adj
* * *n.a glycoprotein, resembling starch, that is deposited in the internal organs in amyloidosis. b-amyloid protein has been found in the brains of Alzheimer's patients but the significance of this is unclear.
* * *am·y·loid (amґə-loid) [amylo- + -oid] 1. resembling starch; characterized by starchlike staining properties. 2. a substance produced by the action of sulfuric acid on cellulose, which gives a blue color when treated with iodine. 3. the pathologic extracellular proteinaceous substance deposited in amyloidosis; it is a waxy eosinophilic material that exhibits a green birefringence under polarized light when stained with Congo red. Amyloid deposits are composed primarily of straight, nonbranching fibrils 7.5â€“10 nm in diameter and of indefinite length, arranged either in bundles or in a feltlike meshwork; each fibril is composed of identical polypeptide chains arranged in stacked antiparallel β-pleated sheets. Although different forms have similar appearance, the protein in each is different.
Medical dictionary. 2011.