Lipids and glucose are primary sources of energy for the body. Lipids are fat-like molecules, and glucose is a type of carbohydrate known as a simple sugar. These compounds have a number of functions in addition to providing energy. They undergo different metabolic processes to fulfill these functions. Various disorders are caused by problems with lipid and glucose processing in the body. It is important to consult with a physician regarding dietary and health choices.
The Basics
Glucose is a single carbohydrate molecule, but it can be linked together to form large chains of carbs, such as starch. In the body, the liver can store glucose by linking glucose units together to form glycogen.
There are many different types of lipids. Cholesterol, fats, fatty acids and the fat-soluble vitamins A, D, E and K are all lipids. In the diet, the main types of fats are monounsaturated, polyunsaturated, saturated and trans fats. Lipids are transported through the body bound to proteins. The lipid-protein complex is known as a lipoprotein. Lipoproteins are classified by their density, such as low density lipoprotein -- LDL -- or high density lipoprotein -- HDL.
Functions
The main function of glucose is to provide energy for cells. Glucose and other sugars can also be modified and attached to proteins. Fats are used to store and release energy for cells. They also cushion the organs and provide insulation. They can be turned into signaling molecules as well. Cholesterol can be metabolized in the adrenal gland and transformed into steroid hormones such as the stress hormone cortisol or the sex steroids testosterone or estrogen.
Metabolism
Glucose undergoes a biochemical transformation called glycosis, which splits the molecule in half, forming two molecules of the chemical pyruvate and generating ATP, which is the main energy donor in the cell. Pyruvate then usually undergoes a series of reactions called the tricarboxylic acid, or Krebs cycle, which generates more energy-carrying compounds and releases carbon dioxide as a waste product. Some of these are used to create even more ATP. Lipids can also be broken down similarly to generate ATP. This process is known as lipolysis.
Disorders
Excessive amounts of glucose are found in type 1 and type 2 diabetes. Type 1 diabetes occurs when the pancreas fails to produce the hormone insulin. Insulin signals cells to take up glucose out of the bloodstream. In its absence, the glucose levels rise in the blood, damaging proteins, blood vessels and organs. In type 2 diabetes, the body does not respond to insulin, also resulting in high glucose levels in the blood.
High levels of lipids in the blood can build up in the arteries, making them narrow and hard, which increases the risk of strokes and heart attacks. One exception is the lipoprotein HDL, which decreases the risk of vascular disease.
References
- "Nutrition Concepts and Controversies (11th edition)"; Frances Sizer et al; 2007
- "Robbins and Cotran Pathologic Basis of Disease (eighth edition)"; Vinay Kumar et al; 2009
- "Harrison's Principles of Internal Medicine (17th edition)"; Dr. Anthony Fauci et al; 2008
- "Physiology (fourth edition)"; Linda Costanzo; 2008
- "Lehninger Principles of Biochemistry (fourth edition)"; David Nelson et al; 2004
