Fat cells do more than just store fat. They control the levels of free fatty acids in the bloodstream, and they function as an endocrine organ. Endocrine organs produce hormones that regulate metabolic activities elsewhere in the body. For example, the pancreas produces insulin, which regulates the storage of fat, protein and glucose. Fat tissue is an endocrine organ because it produces hormones that play a key role in metabolism, appetite control and reproduction.
Fat Cells
Most of the body's fat cells are located under the skin, around internal organs and in breast tissue. Fat cells contain a significantly smaller amount of cytoplasm, or cell liquid, compared to other cells. The rest of the volume of the cell is made up of fat. Each fat cell contains a droplet of fat. When you gain weight, the body does not normally produce more fat cells in response to the extra calorie intake. Rather, the droplet of fat contained in each fat cell gets larger. However, as reported by "The New York Times" on May 5, 2008, the body does generate new fat cells. Each year, 10 percent of your fat cells die and the body generates new ones to replace them. This, however, does not normally happen in response to extra food intake.
Fat Metabolism
When you eat a meal that contains fat, the fat enters your digestive system. Here salts from the gall bladder convert the fat into smaller fat droplets. Lipases from the pancreas convert the fat droplets into glycerol and fatty acids. The fat components convert into triglycerides covered by a protein coating in the cells of the intestine. The protein coating makes it easier for the fat to enter the bloodstream, because protein dissolves more easily in water. From the cells in the intestine walls, the protein-covered fat molecules enter the lymph system and are then passed into the bloodstream.
Fat Storage and Fat Burning
Once the fat molecules have entered the bloodstream, they once again break into fatty acids and glycerol. Just like glucose and the components of protein, these compounds make the pancreas produce insulin. Insulin helps transport the fatty acids to the muscles for energy use and helps store excess fatty acid as droplets of fat, or triglycerides, in fat cells. When there is a shortage of food, the pancreas stops producing insulin and starts producing glucagon instead. Glucagon signals to the cells that energy is needed. The liver and muscles then break down their stored glycogen, and fat cells release fat into the bloodstream for use as energy.
Fat Tissue as an Endocrine Organ
Fat cells are very active cells. They produce hormones that trigger metabolic processes in different parts of the body. The hormones produced by fat cells include estradiol, a precursor to estrogen that controls reproduction, leptin, which controls appetite by binding to receptors on the hypothalamus in the brain, and adiponectin, which controls glucose levels by heightening the body's sensitivity to insulin.
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