Lactic dehydrogenase: An enzyme participating in lactic acid metabolism. Lamins: Proteins that form the nuclear lamina, a polymeric structure intercalated between chromatin and the inner nuclear envelope. Lamins A and C have C terminal sequences homologous to the head and tail domains of keratins, their peptide maps are similar and significantly different from that of lamin B, although there are some common epitopes. Langerhan’s cell: Special types of cells mainly found in the epidermis. They are believed to be antigen presenting cells, this means that these cells process specific antigens and then present them on their surface for further reaction. Laparoscopic: Use of laparoscope, an instrument similar to endoscope to examine the interior of the abdomen. Laparotomy: Surgical incision through abdominal section to gain access to the peritoneal cavity. LDL (low-density lipoprotein): A molecule that is a combination of lipid (fat) and protein. Lipoproteins are the form in which lipids are transported in the blood. Low-density lipoprotein (LDL) transports cholesterol from the liver to the tissues of the body. LDL cholesterol is therefore considered the "bad" cholesterol. Leiomyomas: Benign tumors derived from smooth muscle, most commonly of the uterus; called also fibroid. Leukemia: Cancer of white blood cell. Immature white blood cells (leukocytes) divide without control. Leukopenia: Reduction in the number of leukocytes, the white blood cells, the count being 5000 per cu. mm. or less. Leukoplakia: A white plaque on a mucous membrane that will not rub off. LHRH: Luteinizing hormone-releasing hormone, a hormone that controls sex hormones in men and women. Li--Fraumeni Cancer Syndrome: A syndrome associated with germline mutation of p53 gene. Individual who carries one defective copy of this tumor suppressor gene seems to be prone to develop primary cancer in bone and soft tissues and tumor in other organs due to inactivation of the remaining functional allele. Ligand: Any molecule that binds to another, in normal usage a soluble molecule such as a hormone or neurotransmitter, that binds to a receptor. Linoleic acid: A straight chain, unsaturated, 18-carbon fatty acid with two double bonds, occurring in many vegetable oils. It is an essential fatty acid that cannot be synthesized by animal tissue and must be obtained in the diet. Linolenic acid: It is a straight chain,18-carbon fatty acid with three double bonds. It is an essential fatty acid that cannot be synthesized by animal tissues and must be obtained in the diet. Lipases: Enzymes that catalyze the hydrolysis of fats (monoglycerides, diglycerides and triglycerides) to glycerol and fatty acids. Lipid: Heterogeneous group of fats and fat-like substances characterized by being water-insoluble. Lipids, which are easily stored in the body, serve as a source of fuel, are an important constituent of cell structure, and serve other biological functions. Lipopolysaccharide: A complex of lipid and polysaccharide (carbohydrate). Liposomal: Pertaining to liposome. Liposomes: Spherical particles in aqueous medium, formed by a lipid bilayer enclosing an aqueous compartment. Low-density Lipoprotein: Increase in density corresponds to increase in protein to lipid ratio in lipoproteins. One of the functions of low-density lipoprotein is to carry cholesterol and deposit at various tissues. Luteinizing hormone: A glycoprotein gonadotropic hormone of the anterior pituitary, which acts with the follicle-stimulating hormone to cause ovulation and secretion of estrogen. In the male, it stimulates the development and functional activity of some testicular cells. Luteinizing Hormone-Releasing Hormone Agonist (LHRHa): A compound that is similar to LHRH (luteinizing hormone-releasing hormone) in structure and is able to act like it. Luteinizing hormone-releasing hormone is a naturally occurring hormone that controls sex hormones in both men and women. Thus, an LHRH agonist serves in a manner similar to LHRH to control the same sex hormones. Lymph: The clear, watery, sometimes yellowish fluid containing special white blood cells of immune systems. It travels through the lymphatic system and removes unwanted foreign material from the body. Lymph also supplies lymphocytes to blood and transports fat from intestine. Lymph Node: Lymphoid tissue organized as an organ and is situated along the course of lymphatic vessels and serves as defense mechanism by removing virus, bacteria and toxins. Lymphatic System: The tissues and organs (including the bone marrow, spleen, thymus and lymph nodes) that produce and store cells that fight infection and the network of vessels that carry lymph. Lymphoblast: The immature precursor of the mature lymphocyte. Lymphocytes: Cells of immune system. There are two main types of lymphocytes, B and T with specific functions. Lymphocytic Leukemia: Leukemia associated with the lymphoid cells. Lymphoid: Pertaining to lymph or tissue of the lymphatic system. Lymphoid Cells: Cells of the immune system that react specifically with antigen and produce specific cell products. Lymphokines: General terms for soluble mediators of immune responses that are not antibodies and are synthesized by stimulation with antigen. Lymphoma: Any tumor of the lymphoid tissue; the term lymphoma is often used alone to denote malignant lymphoma. Lypolytic: Agent that destroys fat. Lysosomes: Special membranous structures in the cell containing hydrolytic enzymes to digest proteins, DNA, RNA etc. See diagram on Cell. Lytic agent: Agents that cause breakdown of cells or any structure.