(1) Another word for “fat.” A lipid is more formally defined as a substance such as a fat, oil or wax that dissolves in alcohol but not in water. Lipids contain carbon, hydrogen and oxygen but have far less oxygen proportionally than carbohydrates.
(2) a group of substances comprising fatty, greasy, oily and waxy compounds that are insoluble in water and soluble in nonpolar solvents, such as hexane, ether and chloroform.
Simple lipids are the triglycerides or neutral fats. Each triglyceride molecule is composed of one molecule of glycerol joined by ester linkages to three fatty acid molecules. They are an important source of oxidizable substrate to the body and have a greater caloric density (2.25 times) than carbohydrate.
Compound lipids are important structural components of cell membranes. Phospholipids include lecithin and the cephalins, which are composed of fatty acids linked to phosphatidic acid, and the sphingomyelins, which are composed of fatty acids linked to sphingosine. Glycolipids are composed of a carbohydrate chain and fatty acids linked to sphingosine or ceramide. Cholesterol is a steroid alcohol. Another important function of the phospholipids is as lung surfactants.
lipid A - a component of the cell wall of gram-negative bacteria, responsible for their toxic properties.
lipid, plasma - n the various plasma lipid classes include triacylglycerols, phospholipids, cholesterol, cholesterol esters, and unesterified fatty acids. Because of their hydrophobic nature, plasma lipids are carried in association with specific plasma proteins, the lipoproteins.
lipid pneumonia - aspiration pneumonia due to aspiration of oil.
protected lipids - fats treated to protect them against microbial degeneration in the rumen.
Lipid tests are routinely performed on plasma, which is the liquid part of blood without the blood cells. Lipids themselves are a group of organic compounds that are greasy and cannot be dissolved in water, although they can be dissolved in alcohol. Lipid tests include measurements of total cholesterol, triglycerides, high-density lipoprotein (HDL) cholesterol, and low-density lipoprotein (LDL) cholesterol. Lipid tests may also be performed on amniotic fluid, which is the fluid that surrounds the fetus during pregnancy. Prenatal lipid tests include tests for lecithin and other pulmonary (lung) surfactants that cover the air spaces in the lungs with a thin film.
The purpose of blood lipid testing is to determine whether abnormally high or low concentrations of a specific lipid are present. Low levels of cholesterol are associated with liver failure and inherited disorders of cholesterol production. Cholesterol is a primary component of the plaques that form in atherosclerosis and is therefore the major risk factor for the rapid progression of coronary artery disease (CAD). High blood cholesterol may be inherited or result from such other conditions as biliary obstruction, diabetes mellitus, hypothyroidism, and nephrotic syndrome. In addition, cholesterol levels may be increased in persons who eat foods that are rich in saturated fats and cholesterol, and who lead a sedentary lifestyle.
Low levels of triglyceride are seen in persons with malnutrition or malabsorption. Increased levels are associated with diabetes mellitus, hypothyroidism, pancreatitis, glycogen storage diseases, and estrogens. Diets rich in either carbohydrates or fats may cause elevated triglyceride levels in some persons. Although triglycerides are not a component of the plaque associated with atherosclerosis, they increase the viscosity (thickness) of the blood and promote obesity, which can contribute to coronary disease. The majority of cholesterol and triglyceride testing is performed to screen persons at increased risk of coronary artery disease.
Lipid tests are performed on amniotic fluid to determine the maturity of the fetal lungs. These tests are performed prior to delivery to ensure that there is sufficient pulmonary surfactant to prevent collapse of the lungs when the baby exhales (breathes out).