Unsaponifiable lipids or without fatty acids

The unsaponifiable lipids do not contain fatty acids, so do not form soaps. This group is made up of:

• The terpenes or isoprenoid.
• The steroids. 
• The prostaglandins.

The terpenes or isoprenoid are linear or cyclic molecules formed by the polymerization of the isoprene or 2-methyl-1,3-butadiene .

The classification of terpenes is based on the number of isoprene molecules they contain. According to this number, the following types of terpenes are distinguished:

• the monoterpenes (2 molecules of isoprene),
• the sesquiterpenes (3 molecules),
• the diterpenes (4),
• the triterpenes (6),
• the tetraterpenes (8), and
• the polyterpenes (over 8 molecules of isoprene).

The steroids are lipids derived from the steranes or cyclopentane perhidrofenantreno.

Steroids are divided into: sterols and steroid hormones.

• Sterols.They have a hydroxyl group attached to carbon 3 and an aliphatic chain at carbon 17. Sterols are the largest group of steroids. The main sterols are cholesterol, bile acids, vitamins D, and estradiol.
• Steroid hormones. They are characterized by the presence of an oxygen atom attached to carbon 3 through a double bond. There are two groups of steran-derived hormones: the adrenal hormones and the sex hormones.

Some sterols

Cholesterol

The cholesterol is part of cell membranes of animals, which regulates its flow, giving stability, since it is among the phospholipids. Cholesterol is abundant in the body, and it is the molecule that serves as a precursor to the rest of the steroids.

Bile acids

The bile acids are synthesized in the liver from the cholesterol. The salts of these acids form bile, which is responsible for the emulsion of fats in the intestine during digestion.

Vitamins D

The group of vitamins D regulate calcium metabolism and its intestinal absorption. Each vitamin D comes from a different sterol. Thus, vitamin D₂ or calcinerol is formed from ergosterol, of vegetable origin; the vitamin D₃ or cholecalciferol comes from the cholesterol, etc.

Its synthesis is induced by ultraviolet rays on the skin. Its deficiency causes rickets in children and osteomalacia in adults.

Estradiol

The estradiol is the hormone responsible for regulating the appearance of secondary sexual characteristics female and maturation of the ovum.

Some steroid hormones

They are produced in the cortex of the adrenal glands. The adrenal hormones are:

• The aldosterone, which regulates the functioning of the kidney.
• The cortisol, which is involved in the metabolism of carbohydrates, regulating the synthesis of the glycogen.

Among the sex hormones are:

• The progesterone, which prepares the female sexual organs for gestation.
• The testosterone, responsible for the appearance of male sexual characteristics.

The prostaglandins are lipids whose basic molecule is prostanoato, consisting of 20 carbons forming a cyclopentane ring and two aliphatic chains.

Prostaglandins were discovered in prostate secretions, that is their name. They are synthesized from polyunsaturated fatty acids that are part of the phospholipids of cell membranes.

They have very different functions such as production of substances that regulate the clotting of blood and wound closure; sensitization of pain receptors and initiation of capillary vasodilation, leading to inflammation after blows, wounds, or infections; the appearance of fever as a defense in infections; the decrease in blood pressure by promoting the elimination of substances in the kidney; reducing the secretion of gastric juices, facilitating the healing of stomach ulcers; the regulation of the female reproductive system and the initiation of labor.