Either serving as hormones or hormone precursors aiding in digestion, providing energy storage and metabolic fuel. Acting as functional and storage compounds in biomembranes, or forming insulation to allow nerve conduction and prevention of heat loss. The term lipid applies to a class of compounds that are soluble in organic solvents and nearly insoluble in water. Chemically, a lipid can be either a compound that yields fatty acids to form esters. Lipids also contain nonlipid groups such as sialic, phosphoryl, amino, or sulfate groups which tend to increase their solubility in polar solvents.
Lipids can either be in two dominant forms, exogenous or endogenous.
This means the formation and creation either outside or inside the body respectively. Lipids then have to be transported to tissues and organs throughout the body to perform metabolic functions. Because of their hydrophilic nature, transportation requires hydrophilic adaptation. This allows a series of lipoproteins, called micelles, to transport them throughout the body. Lipoproteins are outer monolayers of proteins and polar lipids with an inner core of neutral lipids.