Lipids are all lipids in living organisms, except for fats, mainly including phospholipids, glycolipids and steroids. Lipids are the main components of biological membranes, can be transformed into important biologically active substances in the body, participate in activities such as intercellular recognition and cell signaling, and are related to biological specificity, etc. They can also constitute plasma lipoproteins. 1. phospholipids: refer to lipids containing phosphate, which are mainly found in brain, bone marrow and nerve tissue, as well as in organs such as heart, liver and kidney, and can be subdivided into glycerophospholipids and sphingolipids. 2. glycolipids. Refers to lipids containing sugar groups, and can be divided into glycerol glycolipids and sphingolipids. Sphingolipids can also be called glycosphingolipids, and important sphingolipids include cerebrosides, gangliosides, blood-type substances, etc.; 3. Steroids: mainly include cholesterol, bile acids, steroid hormones, etc. Cholesterol is abundant in brain and nerve tissues, and can be converted into bile acids and steroid hormones. Bile acid is the main component of bile and exists in bile in the form of sodium or potassium salts. Steroid hormones are divided into adrenocorticotropic hormones and sex hormones, such as aldosterone, corticosterone, cortisol, androgens, estrogens, etc.