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  • Lactose Intolerance: Individuals who are deficient in the intestinal enzyme lactase do not digest or absorb lactose properly. Malabsorbed lactose reaches the large intestine and is fermented by bacteria. Byproducts of the fermentation process cause symptoms, including gas, diarrhea, nausea, and abdominal cramps and bloating.
  • Lamina Propria: Part of the lining of mucous membrane that lines various tubes in the body.
  • Large Bowel: See Large Intestine
  • Large Intestine: A long muscular tube that connects the small intestine with the anus. It is responsible for absorption of water from indigestible food.
  • LES: See Lower Esophageal Sphincter.
  • Leukotriene Inhibitor: A medication that prevents the release of leukotrienes or prevents their proinflammatory action in the body. Several different subtypes of leukotrienes have been identified in association with various inflammatory diseases, hence the development of various different types of leukotriene inhibitor medications.
  • Lipase: The digestive enzyme needed to properly digest lipids, or fats. This enzyme is produced by the pancreas; bile is also needed to digest fats.
  • Liver: The liver is a large solid organ in the right upper corner of the abdomen, and is protected by the rib cage. The liver functions to detoxify chemicals, metabolize drugs, filter blood, and make proteins that are important for blood clotting and other functions. It also produces bile, which is important for digestion, and stores carbohydrates to be used as "fuel" for the body between meals.
  • Lower Esophageal Sphincter (LES): The valve that is located at the bottom of the esophagus where it is connected to the stomach. Improper function of the LES can cause acid reflux.
  • Lower GI Series: See Water Soluble Contrast Enema (Contrast Enema)
  • Lumen: The hollow portion of a tubular body structure, such as the inside of a blood vessel, the intestines, and the esophagus.
  • Lymphocyte: A type of white blood cell that functions as part of the immune system. Types of lymphocytes include: T cells, B cells, and natural killer cells.