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Collagen is the main structural protein in the extracellular space in the various connective tissues in animals. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whole-body protein content. Collagen, in the form of elongated fibrils, is mostly found in fibrous tissues such as tendons, ligaments and skin. It is also abundant in corneas, cartilage, bones, blood vessels, the gut, intervertebral discs and the dentin in teeth.〔Britannica Concise Encyclopedia 2007〕 In muscle tissue, it serves as a major component of the endomysium. Collagen constitutes one to two percent of muscle tissue, and accounts for 6% of the weight of strong, tendinous muscles. The fibroblast is the most common cell that creates collagen. Gelatin, which is used in food and industry, is collagen that has been irreversibly hydrolyzed. Collagen also has many medical uses in treating complications of the bones and skin. The name ''collagen'' comes from the Greek κόλλα (''kólla''), meaning "glue", and suffix -γέν, ''-gen'', denoting "producing".〔O.E.D. 2nd Edition 2005〕 This refers to the compound's early use in the process of boiling the skin and sinews of horses and other animals to obtain glue. ==Types of collagen== Collagen occurs in many places throughout the body. Over 90% of the collagen in the human body, however, is type I.〔Sabiston textbook of surgery board review, 7th edition. Chapter 5 wound healing, question 14〕 So far, 28 types of collagen have been identified and described. They can be divided into several groups according to the structure they form: *Fibrillar (Type I, II, III, V, XI) *Non-fibrillar * *FACIT (Fibril Associated Collagens with Interrupted Triple Helices) (Type IX, XII, XIV, XVI, XIX) * *Short chain (Type VIII, X) * *Basement membrane (Type IV) * *Multiplexin (Multiple Triple Helix domains with Interruptions) (Type XV, XVIII) * *MACIT (Membrane Associated Collagens with Interrupted Triple Helices) (Type XIII, XVII) * *Other (Type VI, VII) The five most common types are: *Type I: skin, tendon, vascular ligature, organs, bone (main component of the organic part of bone) *Type II: cartilage (main collagenous component of cartilage) *Type III: reticulate (main component of reticular fibers), commonly found alongside type I. *Type IV: forms basal lamina, the epithelium-secreted layer of the basement membrane. *Type V: cell surfaces, hair and placenta 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「collagen」の詳細全文を読む スポンサード リンク
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