Class function of steroids

Sterols: widely distributed in the biological world, characterized by a β-hydroxy group on the third carbon atom and a side chain on the 17th position. Some sterols also have a Δ5 double bond. Animal embryonic tissue and skin sterols as well as plant sterols such as
Steroid
Stigmasterol also has a double bond on the side chain. The sterol is present in the living body in free (non-esterified form) or in the form of a fatty acid ester. Sterol is a colorless waxy solid, soluble in organic solvents such as ether, chloroform, benzene and hot ethanol. It is insoluble in water and cannot be saponified (see table). Some important sterols and their sources are listed in the table. 1 animal sterol: cholesterol, also known as cholesterol. An important component of vertebrate cells, with the highest content in the nervous tissues and adrenal glands (percent wet weight), the lowest content in the heart, and a considerable amount in the liver, kidneys and skin. The gallstones in the human body are mainly composed of cholesterol. Normal human plasma cholesterol content is 150-250 mg per 100 ml, and the ratio of free to esterification is about 1:3. The main esterified fatty acids are linoleic acid, followed by oleic acid, followed by saturated acids (mainly palmitic acid) and arachidonic acid. The cholesterol content in human red blood cells is about 100 mg per 100 ml of packed cells, almost all free cholesterol; it is in dynamic equilibrium with plasma free cholesterol. The nerve tissue mainly contains free cholesterol and is not exchanged with other cholesterol stores in the body. The adrenal glands and gonads are rich in esterified forms of cholesterol. Mammalian cells (except mature red blood cells) can synthesize cholesterol, but the rate of synthesis varies widely. The liver and small intestine are the main sites of synthesis. Animals can also take cholesterol from food. Its physiological function is not fully understood. Cholesterol is a component of the cell membrane and organelle membrane. The plasma membranes of red blood cells, liver cells and myelin contain a considerable amount of cholesterol; it regulates the physical state of biofilm lipids and maintains the fluidity of the membrane. The nerve myelin contains a lot of cholesterol. It has a relationship with the formation of myelin, maintaining stability and function. In addition, cholesterol is a precursor to the synthesis of bile acids and steroid hormones. 7-dehydrocholesterol is present under the skin of animals and can be converted to vitamin D3 under ultraviolet light. 2 phytosterols: Phytosterols are important components of plant cells and cannot be absorbed and utilized by passive objects. Both stigmasterol and sitosterol are derivatives of myristal, two more carbon atoms than cholesterol and one ethyl group on C-24. 3 Yeast sterol: Ergosterol is the main sterol component of yeast and ergot. A steroid compound containing 28 carbon atoms. It is converted into vitamin D2 by ultraviolet light irradiation. Vitamin D plays a key role in the homeostasis of calcium and phosphorus in animals. Steroid hormones: ecdysone of insects and crustaceans is a derivative of cholestane, characterized by a double bond between C-7 and C-8, a C-6 keto group, 2β, 3β, 14α hydroxy and a side chain C- 22 and C-25 hydroxyl groups. The thymus of the insect's anterior thymus and crustacean secretes ecdysone, a hormone necessary for molting and growth regulation. Plants also have potent ecdysone analogs with ergosterol and myristane side chain structures.
Cardiac glycosides: Many species of plants contain derivatives of strong alkyl lactide, also known as steroid compounds, usually in the form of glycosides in nature. The medicinal cardiac glycoside has foxglove toxin, quercetin and digoxin; its role is to strengthen myocardial contractility, slow heart rate, and is used to control heart failure. Saponin ligand: present in plants, is a derivative of spirooxane, which is combined with a sugar to form a glycoside, saponin, by a 3β-hydroxy group. It is named for its ability to form a soapy solution and is surface active. The structure of dioxin in Dioscorea has been clarified, and the structure of many saponin ligands has also been reported. Diosin ligands and agave saponins are often used as raw materials for the manufacture of steroid hormones.