什麼是膽固醇
存在血漿和所有動物組織內的一種蠟狀物質。是一種類固醇,分子式為C2746。膽固醇為生命所必需,它是細胞膜的重要組成,為體內合成膽酸、類固醇激素和維他命D的原料或中間產物。膽固醇並不溶於血,故須附於某些蛋白質複合體(稱為脂蛋白)上,方能於血液中運輸。它是由肝臟和其他一些器官制造,以飲食攝取量的多寡來調節。血中膽固醇過高會沈積在血管內壁上(參閲arteriosclerosis),導致冠狀動脈心臟病。1985年布朗(M. Brown, 1941~)和戈德斯坦(Joseph Goldstein, 1940~)因發現這個過程而共獲諾貝爾醫學或生理學獎。避免血膽固醇過高的最佳對策為降低飲食中的膽固醇攝取量以及減少動物性脂肪(如飽和或過飽和脂肪)的攝取量。參閲triglyceride。
cholesterol
Waxy organic compound found in blood and all animal tissues. It is a steroid, with molecular formula C27H46O, containing four rings in its structure. Cholesterol is essential to life; it is a primary component of cell membranes and a starting or intermediate material from which the body makes bile acids, other steroid hormones, and vitamin D. It is made in the liver and some other organs, in greater or lesser amounts depending on the amount recently consumed in the diet. It circulates in the blood in compounds called lipoproteins, since it is not water-soluble alone. Excess cholesterol in the blood forms deposits in arteries (see arteriosclerosis), which can lead to coronary heart disease. Michael Brown (born 1941) and Joseph Goldstein (born 1940) won a Nobel Prize in 1985 for their work in discovering this process. Since the body makes cholesterol from fats, blood cholesterol cannot be reduced by limiting only the amount of cholesterol in the diet; the amount of fat, especially saturated fat (see saturation, fatty acid) must also be reduced. See also triglyceride.
-
什麼是酶催化劑
即指酶,一類由生物體產生的具有高效和專一催化功能的蛋白質。酶催化劑和活細胞催化劑均可稱為生物催化劑。在生物體內,酶參與催化幾乎所有的物質轉化過程,與生命活動有密切關係;在體外,也可作為催化劑進行工業生產。酶有很高的催化效率,在温和條件下(室温、常壓、中性...
-
什麼是時行感冒
感受時行病毒所引起的急性呼吸道傳染性疾病。西醫學稱為流行性感冒。全身症狀明顯,臨牀以突然惡寒、發熱、頭痛、全身痠痛為主要特徵。一年四季均可發生,冬春兩季較為多見。起病急驟,傳播迅速,傳染性強,常可引起大流行。時行感冒的病因多與氣候突變、寒温失常有關,如...
-
什麼是激素
由內分泌細胞合成和分泌的、能將一定的化學信息傳遞到靶細胞併產生生物效應的微量化學物質。過去人們認為,激素是由體內無導管的內分泌腺體產生並直接分泌進入血液循環,轉運到遠處的靶器官發揮一定的生理作用。現已知激素的產生不限於傳統的內分泌腺體,激素的轉運...
-
什麼是環境污染
自然的或人為的原因使某些化學的、物理的、生物的有害因素帶入人類賴以生存的空氣、水、土壤和食物等環境中的現象。人的生活環境中有着各種污染源,污染物質從各種污染源排出,通過人的呼吸、飲食,使人體健康和精神狀態受到直接或間接的、近期和遠期的(遺傳的)不利影...