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1-10 A B C D E F G H I J K L M N O P Q R S T U V W XYZLabeled
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The term "labeled" means to mark substances in a way that they can easily be identified. In life sciences, substances in the body are labeled using stable isotopes or harmless radioactive components so that they can be traced, analyzed or measured.
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Labeled water (H218O) is a naturally occurring form of water which contains the rare 18O isotope of oxygen (the common isotope of oxygen is 16O).
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Lability means instability, or easily altered or modified, e.g. chemical instability.
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The labyrinth is the system of cavities and tubes that comprises the inner ear of vertebrates. It consists of a system of membranous structures housed in a bony cavity.
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Labyrinthine means relating to the labyrinth.
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Lactate dehydrogenase (LDH) describes a group of four enzymes involved in the oxidation of lactate to pyruvate.
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Lactic (or lactate) Dehydrogenase (LDH) is an enzyme found in many body tissues especially heart, liver, kidney, skeletal muscle, brain blood cells, and lungs and is involved in basic cellular metabolism. Measurement of LDH isoenzymes is helpful in differentiating the source (location) of tissue damage. LDH exists in 5 forms, called isoenzymes, which differ slightly in structure. LDH-1 is in highest concentrations in heart muscle and red blood cells. LDH-2 is highest in white blood cells. LDH-3 is highest in the lung. LDH-4 is highest in the kidney, placenta, and pancreas. LDH-5 is highest in the liver and skeletal muscle. All of these isoenzymes can be measured in the blood.
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Lactulose is a nonabsorbable synthetic sugar which is used as a cathartic (laxative) in chronic constipation or in the treatment of hepatic coma.
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Laminar flow is a nonturbulent flow in parallel layers that have different velocities.
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Landing refers to the day and time when the spacecraft returns back to Earth. It is sometimes abbreviated as R+0 to indicate zero days after landing day.
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The large intestine consists of the cecum, vermiform appendix, colon, and rectum. Its primary role is the excretion of non-absorbed material passed from the small intestine, and water absorption.
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Larvae refers to the juvenile stage of most invertebrates, amphibians, and fish, which all hatch from eggs. It is unlike the adult in form and is usually incapable of sexual reproduction. It develops into the adult by undergoing metamorphosis. Examples are the tadpoles of frogs or caterpillars of butterflies.
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Larynx is the upper part of the respiratory tract between the pharynx and the trachea, having cartilaginous walls and containing the vocal cords.
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A laser is a device that concentrates high energies into a narrow beam of non-spreading, monochromatic light.
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Latency refers to the period between nerve stimulation and response.
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A latent infection is an infection by a virus in which the virus lays dormant in the host cell.
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The term lateralis indicates that a structure is located away from the mid-line of the body.
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Lean body mass refers to the weight of the body minus the fat content, or, in other words, the body mass without the fat.
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An LED is a Light Emitting Diode; a very small light often used in electronic instrumentation.
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Left Ventricular Stroke Volume, also called stroke volume, is the volume of blood (normally about 70 ml) ejected into the aorta during the contraction of the heart's ventricles.
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Leg volume refers to the actual volume of the leg, a measurement taken to indicate changes in muscle size, either associated with changes in muscle size, or in the amount of fluid located in the tissues of the leg. Often taken during space flight or bed rest studies that are investigating changes in fluid volume or muscle size.
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A lentil is the round, flattened, edible seed of a pea-like Old World plant also called a lentil. It is a member of the leguminosae group - plants with the ability to use nitrogen in the air for nutrition.
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A leptocyte is a red blood cell characterized as being thin and flat in appearance.
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A lesion is a scar, or tissue that is damaged.
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Leukemia is any group of malignant diseases in which the bone marrow and other blood forming organs produce increased numbers of leukocytes (white blood cells).
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A leukocyte is a white blood cell, specifically a colorless cell with a nucleus, found in blood and lymph. Leukocytes are capable of amoeboid movement. They can produce antibodies and move through the walls of vessels to migrate to sites of injury, where they isolate and destroy dead tissue, foreign protein and bacteria.
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Leukocytosis is an abnormal increase in the number of circulating white blood cells, which usually accompanies bacterial, but not viral, infections. Types of leukocytosis are basophilia, eosinophilia, and neutrophilia.
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Leukopenia is a reduction in the number of white blood cells (leukocytes) in the blood.
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Libration is an oscillation in the apparent aspect of a secondary body (such as a planet or satellite) as seen from the primary object around which it revolves.
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Libration clouds are small celestial particles trapped in regions of the Earth-Moon system where gravitational and centrifugal forces acting on them cancel each other.
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Life support systems are the hardware and resources that provide the necessities vital for life, namely, oxygen, water and food for space travelers. Temperature regulation, carbon dioxide removal and waste management systems are considered subsystems of life support systems.
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Ligaments are resilient but flexible tissues which hold two or more bones together at a movable joint. Ligaments restrain the movement of bones at a joint and are therefore important in preventing dislocation. They consist primarily of collagen.
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Light flash phenomenon is a visual phenomenon or event that is experienced when a person is exposed to cosmic ionic particles, similar to (but brighter) as a shooting star on the night sky. Although the exact mechanism that causes this phenomenon is unknown, it is believed that visual flashes result from direct ionizing energy loss as the particle traverses the cells of the eye.
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Light microscopy is the inspection of a substance or object with the use of a light microscope. A light microscope uses visible light to help provide an enlarged image of an object or substance that is very small or not visible to the naked eye.
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The light unit of the Svet greenhouse is inserted into the top of the growth chamber and can be set at three different positions, at distances of 20, 30 and 40 centimeters from the root module surface, to allow for maximum illumination during plant growth. It contains six units that each contain fluorescent bulbs.
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Linear acceleration is the rate of change of velocity in a linear direction (along a straight line) with respect to time.
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Lipase is an enzyme, secreted by the pancreas and the glands of the small intestine, that breaks down fats into glycerol and fatty acids during digestion.
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A lipid is one of a group of naturally occurring compounds, also known as fat, that are soluble in organic solvents such as chloroform or alcohol, but insoluble in water. Lipids are important dietary constituents, not only because of their high energy value, but also because certain vitamins and essential fatty acids are associated with them.
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Scintillation counting is a technique for measuring the quantity of a radioactive isotope present in a sample. In biology, liquid scintillation counting is mainly used for isotopes such as carbon 14, sulfur 35 and phosphorous 32 and particularly for the low energy emission of hydrogen 3. Gamma emissions are often measured by counting the scintillations that they cause in a crystal. Autoradiographic images can be enhanced by using a screen of scintillant behind the film.
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Liquid-liquid diffusion is a method used for protein crystal growth in which a liquid precipitant solution is in contact with, but not mixed with a protein solution. The molecules of the precipitant diffuse into the protein solution to yield protein crystals.
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Lithium chloride is a substance used as an inert tracer in the determination of fluid volume by the lithium dilution technique.
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The liver is the largest gland of the body, weighing between 1200-1600 grams, and is situated in the top right portion of the abdominal cavity. The liver is divided by fissures into four lobes. The liver plays an essential role in many metabolic processes by regulating the composition and concentration of nutrients and toxic materials in the blood. Its functions include synthesizing bile and blood coagulating factors, acting as the site of metabolism of carbohydrates, proteins and fats, regulating the amount of blood sugar, converting excess glucose to glycogen, removing excess amino acids, storing and metabolizing fats, and detoxifying poisonous substances, worn out red blood cells and other unwanted material.
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A load is the overall force to which a structure is subjected in supporting a weight or mass or in resisting externally applied forces
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The term loading refers to gravitational loading, or the application of force to a bone or part of the body. Under normal circumstances on Earth, gravity "loads" the bones and muscles with the force required to support the body.
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Locomotion is the act of moving, or the ability to move, from place to place.
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Locomotor refers to locomotion, the ability of an organism to move in a particular direction in its environment. In animals, the force required to initiate locomotion is generated by voluntary muscle contractions.
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The locus ceruleus is a small pigmented region in the floor of the fourth ventricle of the brain; the region is made up of about 20,000 melanin-pigmented neuronal cell bodies whose norepinephrine-containing axons have a remarkably wide distribution in the cerebellum as well as in the hypothalamus and cerebral cortex of the brain.
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Lomotil is the trademark for an antidiarrheal fixed-combination drug containing an antiperistaltic and an anticholinergic.
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The longissimus is the intermediate division of the erector spinae muscle having three subdivisions: musculus longissmus capitus (keeps the head erect), m. l. cervicus (extends cervical vertebrae) and m. l. thoracis (extends the vertebral column).
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Lordosis is the normal curvature of the lumbar and cervical spine, seen as an anterior concavity if the person is observed from the side.
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To apply lower body negative pressure (LBNP), the lower body (legs and hips) is placed in a sealed chamber. If suction is applied to the chamber, this causes body fluid to move from the chest and upper body to the lower body. This shift of fluid is very similar to the shift of fluid that occurs when people stand upright.
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Lumbar means relating to the loins, or the part of the back and sides between the ribs and the pelvis.
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The lumbar 3 is the third vertebrae (counted from the head) of the lumbar spine.
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The lumbar spine, or lumbar vertebrae, are the five bones of the backbone that are situated between the thoracic vertebrae and the sacrum in the lower part of the back. They are the largest of the unfused vertebrae and have stout processes for attachment of the strong muscles of the lower back.
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The lumbar vertebrae are the five bones of the backbone that are situated between the thoracic vertebrae and the sacrum in the lower part of the back. They are the largest of the unfused vertebrae and have stout processes for attachment of the strong muscles of the lower back.
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Lumbo-sacral refers to the group of motor neurons which connect the lower spinal cord to muscles of the lower back, gluteal region, and various other parts of the body.
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Luminous means emitting light.
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Lung water is the fluid in the pulmonary extravascular space. Excessive water accumulates in the lung during disease or when edemas are present. The lung water causes impaired perfusion and breathing, depriving the body of oxygen.
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Lymph nodes are one of a number of small swellings found at intervals along the lymphatic system. Groups of nodes are found in many parts of the body; for example, in the groin and armpit and behind the ear. They are composed of lymphoid tissue and act as filters for the lymph, preventing foreign particles from entering the bloodstream; they also produce lymphocytes.
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Lymphocytes are a variety of white blood cells present in blood, lymph nodes, spleen, thymus gland, gut wall and bone marrow. Important to the immune system, they produce circulating antibodies and T-lymphocytes, which are primarily responsible for cell-mediated immunity and can differentiate into helper, killer or suppressor cells.
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Lymphocyte proliferation means that after lymphocytes encounter an antigen or foreign protein, they begin a process by which they rapidly reproduce themselves, so that there are many lymphocytes available which can recognize and fight the invading antigens.
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A lymphokine is a soluble substance released by sensitized lymphocytes on contact with specific antigen, which help effect cellular immunity by stimulating activity of monocytes and macrophages. These include chemotactic, mitogenic, migration-inhibitory, transfer factors, lymphotoxin and immune (antigen) interferon.
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A lymphoma is any malignant tumor of the lymph nodes, including Hodgkin's disease.
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Lymphopenia is a decrease in the number of lymphocytes (a variety of white blood cells) in the circulating blood, which may occur in a wide variety of diseases.
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Lyophilized or lyophilization is the process of freeze-drying, which is the removal of liquid from heat-sensitive materials. The material is frozen, placed under a high vacuum, and maintained at a low temperature. The pressure generated by the vacuum causes the ice to turn from a solid to a gaseous form without passing through a liquid state.
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Lysis is a rupture of cell membranes and loss of cytoplasm.
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Lysozyme is an enzyme that hydrolyzes the 1,4-beta links between N-acetylmuramic acid and N-acetylglucosamine, and thus destructive to cell walls of certain bacteria. It is present in tears and other body fluids, in egg whites and in some plant tissues.