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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 XYZAberration
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Aberration refers to straying from the normal situation; deviant development or growth.
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An abscess is a circumscribed collection of pus appearing in an acute or chronic localized infection, and is associated with tissue destruction and swelling.
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Absolute Lymphopenia is the reduction in the total number of lymphocytes in the blood.
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Absolute Neutrophilia refers to the increase in the total number of leukocytes in the blood as well as an increased percentage of neutrophils.
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An absorbed dose is the quantity of radiation received per unit of mass within a given period of time. The unit is the gray (Gy), although it is often measured in rads (1 rad = 0.01 gray).
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An absorptiometer is a device that measures photon radiation. An absorptiometer consists of at least three essential components: (1) a source of electromagnetic (photon) radiation in the proper energy region, (2) a cell that is transparent to the radiation and that can contain the sample, and (3) a detector that can accurately measure the intensity of the radiation after it has passed through the cell and the sample.
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Absorptiometry is a technique that measures the amount of radiation absorbed by any substance or chemical constituent of blood, urine or other body fluid that is analyzed (analyte). Essentially, the amount of absorbed radiation increases with the concentration of the analyte and with the distance through the analyte that the radiation must travel (the cell path length). As radiation is absorbed in the sample, the intensity of the radiative beam decreases. By measuring the decreased intensity through a fixed-path-length cell containing the sample, it is possible to determine the concentration of the sample. Because different analytes absorb at different wavelengths (or energies), the device that measures the radiation must be capable of controlling the wavelength of the incident electromagnetic (photon) radiation. When measuring bone mineral content, the radiation sources used emit radiation within a narrow wavelength band.
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Absorption is the uptake of fluids or other substances by the tissues of the body. Digested food is absorbed into the blood and lymph from the alimentary canal. Most absorption of food occurs in the small intestine.
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Acceleration is the rate of change of velocity with respect to time.
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An accelerometer is a device which can measure acceleration, the rate of change of velocity with respect to time.
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An accessory cell is a blood cell, usually a monocyte, that secretes a substance (such as interleukin-1) required for activation of lymphocytes in the immune response.
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Acetaminophen is a commonly used pain-relief medication.
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Acetylcholine is released at nerve endings to pass on a nerve impulse to the next nerve or to initiate muscular contractions. The released acetylcholine is rapidly broken down by the enzyme acetylcholinesterase to allow the transmission of following (subsequent) impulses.
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Acetylcholinesterase is an enzyme that breaks down the neurotransmitter acetylcholine (a chemical which initiates muscular contraction) into choline and acetic acid, rendering it inactive or unable to transmit a signal, therefore, stopping or regulating the nerve signals.
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Acetylene is a colorless, odorless explosive hydrocarbon gas. Its formula is C2H2, and in high concentration of 40 volumes per cent and higher it has the effect of an anesthetic.
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The Achilles tendon is a fibrous band that connects the triceps surea (the calf muscle) with the calcaneus (heel bone).
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Acid citrate dextrose contains trisodium citrate (dihydrate), citric acid and glucose. It is an anticoagulant agent that keeps blood from clotting, or forming into a solid or gel.
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Acid phosphatase is an enzyme with acidic pH optimum, that catalyzes cleavage of inorganic phosphate from a variety of substrates. Found particularly in lysosomes and secretory vesicles. Can be localized histochemically using various forms of the Gomori procedure.
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Acinetobacter calcoaceticus bio. anitratus is a species of bacteria originally found in environments containing quinic acid. It is a nonmotile, aerobic bacterium in the form of gram-negative short rods and does not produce spores. One of its strains is commonly found in the genitourinary tract of humans.
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Acini are the small gas exchange regions of the lung.
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Adrenocorticotropic hormone (ACTH) is a hormone synthesized and secreted by the anterior pituitary gland. ACTH is produced in response to stress and controls the secretion of certain hormones by the adrenal glands.
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Actifed is a trademark for a fixed-combination drug containing an adrenergic vasoconstrictor and an antihistamine.
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Actinometry is used to measure the ability of radiant energy in the visible and ultraviolet spectral regions to produce chemical changes. Actinometry can also measure the direct heating power of the sun's rays.
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The action potential conduction velocity is the measure of the velocity of a nerve impulse (or action potential) from a specified initial point to an end point on a nerve fiber. The change in voltage that occurs across the membrane of a nerve or muscle cell when a nerve impulse is triggered is called an action potential; it is caused by the passage of charged particles across the membrane (depolarization).
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To activate is to set in motion; to make active.
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An actuator is a device responsible for putting a mechanical device into motion.
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Acuity is clarity or distinctness of hearing or sight.
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Ad libitum means without restraint.
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An adductor is any muscle that draws a body part toward the median plane of the body.
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The adductor longus is one muscle of the inner thigh. It is the muscle that allows the thigh bone (femur) to move.
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ATP (adenosine 5'-triphosphate) is a nucleotide that is of fundamental importance as a carrier of chemical energy in all living organisms. ATP can undergo hydrolysis, a reaction triggered by ATPase, which releases a large amount of energy that is used to fuel such biological processes as muscle contraction or the active transport of ions and molecules across cell membranes, or the synthesis of biomolecules.
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Adenoviruses are viruses containing double-stranded DNA. They cause latent infections in mammals and birds of the upper respiratory tracts, and produce symptoms resembling those of the common cold.
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Antidiuretic Hormone (ADH) is a hormone (also called vasopressin) produced and released in the posterior pituitary gland. It stimulates the kidneys to absorb water from produced urine, and thus controls the water content of the body.
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The term adrenal refers to the adrenal glands (a pair of endocrine glands) located on the kidneys' surface. These glands are responsible for the secretion of adrenalin along with other regulatory hormones.
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The adrenal cortex is the outer region of the adrenal gland, in which several steroid hormones are produced.
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Adrenalectomized (or adrenalectomy) means having one or both adrenal glands removed.
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Adrenergic refers to neurons that use catecholamines (epinephrine, norepinephrine, etc.) as neurotransmitters at a synapse when a nerve impulse passes, i.e., the sympathetic fibers. Adrenergic also refers to neurons that are activated by, characteristic of, or secrete adrenaline or substances with similar activity.
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Adrenergic receptors are receptors of nerve cells or fibers of the nerve systems that employ norepinephrine or epinephrine as their neurotransmitter (to transmit a signal from one nerve cell to the next).
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Adrenocortical means of, relating to, or derived from the cortex of the adrenal glands.
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Adrenocorticotropic Hormone (ACTH) is a hormone of the anterior pituitary gland that stimulates the growth of the adrenal gland cortex and the secretion of corticosteroids. ACTH secretion, regulated by corticotropin releasing factor (CRF) from the hypothalamus, increases in response to a low level of circulating cortisol and to stress, fever, acute hypoglycemia, and major surgery.
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The AEM (Animal Enclosure Module) is designed to house up to 16 rats on the Shuttle. The animals can be monitored through the plexiglass ceiling of the module.
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Aerobic means living in air. Aerobic can also describe a type of cellular respiration in which foodstuffs (usually carbohydrates) are completely oxidized into carbon dioxide and water with the production of chemical energy, in a process requiring atmospheric oxygen.
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Afebrile means without fever.
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Afferent is a general term applied to nerves or blood vessels that means nerve signals or blood are traveling from the peripheral to the center of the body.
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Agar is an extract of certain seaweeds that forms a gel suitable for the solidification of liquid bacteriological culture media.
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Agglutinate means to cement or unite together.
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Agglutination is the clumping or sticking together of cells, such as red blood cells or bacteria, so that they form a visible pellet-like clump. Agglutination can be a reaction of the red blood cells, closing an injury in the skin, or by antibodies.
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An aggregate is a group of cells that are attached together.
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Aggregation means to unite or come together in a mass or cluster.
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Agonist describes a drug, hormone or transmitter substance that forms a complex with a receptor site and triggers an active response from a cell (in other words, a drug capable of initiating actions is an agonist). Also, an agonist is a muscle whose active contraction causes movement of a part of the body.
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Alanine is a nonessential amino acid found in many food protein sources as well as in the body.
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Albumin is a type of simple protein widely distributed throughout the tissues and fluids of plants and animals; it is characterized by being soluble in water but forms insoluble coagulates when heated. Albumins occur in egg white, blood, milk, and plants.
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Aldosterone is the principal electrolyte-regulating steroid secreted by the adrenal cortex; it controls excretion of potassium by the kidneys and thereby maintains the balance of sodium and water in the body fluids.
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An algorithm is any mechanical or repetitive procedure used in the management of health problems.
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An aliquot, in chemistry and immunology, pertains to a portion of the whole; loosely, any one of two or more samples of something, of the same volume or weight.
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Aliquote (verb) is to divide into equal portions.
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Alkaline phosphatase is an enzyme that catalyses the hydrolysis of phosphoric acid esters under conditions of alkaline pH. In humans, the level of alkaline phosphatase in the blood is measured as part of the assessment of liver function. In the blood, the enzyme also breaks down phosphates required for mineralization of bone. There are two distinct forms of the enzyme, liver alkaline phosphatase and bone alkaline phosphatase.
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Alkalosis is an abnormal condition of body fluids, characterized by a tendency toward a pH level greater than 7.44, usually caused from an excess of alkaline bicarbonate or a deficiency of acid. Respiratory alkalosis may be caused by hyperventilation, resulting in an excess loss of carbon dioxide and a carbonic acid deficit. Metabolic alkalosis may result from an excess intake of or retention of bicarbonate, loss of gastric acid in vomiting, potassium depletion or any stimuli that increases the rate of sodium-hydrogen exchange.
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Allantoic fluid is fluid of the allantois, a fetal membrane developing from the hindgut (or yolk sac, in man). In man it is vestigial; externally, in mammals, it contributes to the formation of the umbilical cord and placenta; in birds and reptiles it lies close beneath the porous shell and serves as an organ of respiration.
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An allergen is any anitigen that causes allergy in a hypersensitive person. Allergens are diverse and affect different tissues and organs. Examples of allergens include pollen, fur, feathers, dust and mold.
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An alloy is composed of a mixture of two or more metals.
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An alpha globulin is a type of protein present in plasma. Alpha globulins perform diverse functions in the circulation, such as transporting various substances by combining reversibly with them, transporting other proteins from within the body, and acting as substrates for the formation of other substances.
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Alpha-1-antitrypsin, a glycoprotein, is a major protease inhibitor of human serum and is produced in the liver. It protects tissues from digestion and blocks the action of target enzymes by binding nearly irreversibly to their active site.
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Many Shuttle-Spacelab missions have assigned alternate payload specialists. The alternate payload specialists receive the same training as the flight payload specialists. Until one month before flight, the alternate payload specialist acts as a backup and can replace the flight payload specialist, if necessary. During the mission, the alternate payload specialists will remain on the ground (unless they replace the primary crewmember) and act as the prime communicator with the payload crew in space.
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Altitude refers to the height above sea level of a given point.
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Alveolar refers to alveoli, air sacs of microscopic size in the lung whose function is to facilitate the exchange of oxygen and carbon dioxide from the air to blood.
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The alveolar epithelium is the tissue that covers the external surface of the alveoli (air sacs of microscopic size in the lung whose function is to facilitate the exchange of oxygen and carbon dioxide from the air to blood).
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Alveolar ventilation is the passage of air into and out of the alveoli (microscopic sacs in the lungs wherein gas exchange occurs).
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Ambient describes the conditions and factors in the immediate environment. For example, the ambient temperature is the local temperature. The term is also used to describe room temperature (20°C, 70°F).
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Amino acids are the building block of protein. Amino acids join together and form short chains (peptides) or much longer chains (polypeptides). Over 80 amino acids are known to occur naturally,with 20 found commonly in protein polypeptides.
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An amphibian is an organism, such as a frog, toad, salamander, or some types of newts, having an aquatic early stage (e.g. tadpole) and developing air-breathing lungs as an adult (e.g. frog).
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An ampoule is a small glass vial sealed after filling (chiefly used as a container for a hypodermic injection solution).
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Amylase is an enzyme that occurs in saliva and pancreatic juice and aids the digestion of starch and other polysaccharides, which it breaks down into glucose, maltose and dextrins.
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Amyotrophy is muscular wasting or atrophy.
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Anabolism is the metabolic process by which simple substances are synthesized into the complex materials of living tissue.
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Anaerobic refers to an environment or a condition which is free of oxygen or describes a microorganism which can grow in the absence of oxygen.
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An analog transmission mode is one in which data is represented by a continuous electronic signal. In an electronics system, analog, often referred to as linear, refers to measuring a continuous stream of varying voltage levels.
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Androsterone is a steroid metabolite found in male urine and having weak androgenic potency.
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Anemia is a condition characterized by oxygen carrying deficiency caused by a low amount of red blood cells, iron deficiency, or sickle cell formation of red blood cells.
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Aneroid means not containing a liquid, used especially to describe a device in contrast to one performing a similar function that does not contain liquid, such as an aneroid sphygmomanometer, which does not contain a column of mercury.
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Atrial natriuretic factor (ANF) is a hormone-like substance present in the two atrial walls of the heart (especially numerous in the right atria). The ANF factor can cause a three to ten times increase in renal (kidney) excretion of sodium when it is fully released into the circulating blood. Consequent to the loss of sodium is a slight decrease in the extracellular fluid volume and blood volume. Although its exact mechanism of action is unclear, it is believed that the ANF plays a role in the regulation of blood volume.
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ANF (or atrial natriuretic factor) receptors are a group of cells specialized to detect changes in the blood pressure. They are located within the atrial walls of the heart. Although the mechanism of the action of ANF receptors is not completely understood, it is believed that when excess blood volume stretches the atrial walls, ANF receptors located in the walls are triggered to release atrial natriuretic factor into the circulating blood. The ANF causes sodium (and water) to be excreted from the kidneys and blood volume to be reduced.
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Angiotensin is a family of vasoconstrictor substances (which causes narrowing of the blood vessels), present in the blood; it is formed by the action of renin upon a globulin formed by the liver. It helps regulate blood pressure.
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An anion is a negatively charged ion.
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The ankle dorsiflexor (tibialis anterior) is the calf muscle which causes the foot to turn upward.
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Annotation is a critical or explanatory note; a commentary.
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An anode has a negative electrical load; all positive loaded ions move towards the anode.
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An anomaly is a deviation from the common rule; an irregularity.
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ANOVA, or Analysis of Variance, is a statistical technique by which sets of measurements are investigated to determine the extent of experimental or chance influences on individual measures.
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Anoxia is an abnormal condition characterized by a lack of oxygen. Anoxia may be local or systemic and may be the result of an inadequate supply of oxygen to the respiratory system or of an inability of the blood to carry oxygen to the tissues, as in anemic anoxia, or an inability of the tissues to absorb the oxygen from the circulating blood, as in histotoxic anoxia.
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ANP receptors are cell membrane bound molecules in the kidney's tubules which bind to atrial natriuretic peptide and promotes natriuresis, the excretion of sodium.
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An antagonist refers to a muscle in a passive state, while the opposing muscle, the agonist, is active.
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The antecubital fossae is the front area where the arm bends at the elbow.
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An antenna is a metallic instrument used for transmitting and receiving electronic signals.
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Anterior describes or relates to the front (or ventral) portion of the body, an organ or the limbs.
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Anterior horns are the inner substance of the human brain, or the gray matter. The gray matter builds two "horns"; the one pointing toward the face is called the anterior horn, the one facing towards the neck is called the posterior horn.
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Anthropometric refers to a branch of anthropology (the science of studying humans in all their relations), that deals with making comparative measurements of the human body. In space flight, for instance, the length of the spinal column is measured before and during flight to see if the vertebrae expand in space.
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Anthropometry is the study of anthropometrics. Anthropometry is a branch of anthropology (the science of studying humans in all their relations), that deals with making comparative measurements of the human body. In space flight, for instance, the length of the spinal column is measured before and during flight to see if the vertebrae expand in space.
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An antibiotic is a substance, produced by or derived from a microorganism (especially mold), that destroys or inhibits the growth of other microorganisms. Antibiotics are used to treat infections caused by organisms that are sensitive to them, usually bacteria or fungi.
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An antibody is a special kind of blood protein secreted by B-lymphocytes, a type of white blood cell in the immune system. Antibodies are synthesized in response to the presence of a particular antigen (foreign or potentially dangerous substances such as bacteria and viruses) and they circulate in the bloodstream to attack the antigen and render it harmless. Antibodies bind to the antigen causing less damage to occur and helping white blood cells destroy the foreign object.
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An antibody titer is a measure of antibody quantity.
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Anticipatory postural activity describes the reflexes which prevent the body from falling to the ground in the event of an unexpected lean that sends the body out of balance. These reflexes activate the muscles before the brain can react to the change the posture. People who don't have good anticipatory postural reflexes are more likely to fall over if they are suddenly pushed.
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Antidiuretic Hormone (ADH) is a hormone (also called vasopressin) produced and released in the posterior pituitary gland. It stimulates the kidneys to absorb water from produced urine, and thus controls the water content of the body.
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An antigen is any substance that the body regards as foreign and which therefore triggers an immune response; antigens are usually proteins associated with bacteria and viruses.
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Antigenic means allergenic or having the properties of an antigen.
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The antigravity muscles, located in the legs, trunk and neck, function primarily to support the body against the pull of gravity; the relative degree of contraction of the individual antigravity muscles is determined by the equilibrium mechanisms, which are controlled by signals mainly from the vestibular apparatuses (sensory organs for equilibrium).
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Antihypotensive means of or pertaining to the a substance or procedure that increases low blood pressure.
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An antioxidant is a substance that slows or prevents oxidation reactions, and is commonly added to prepared foods, vegetable oils and paints to prevent deterioration upon exposure to oxygen.
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Antipyrine is a substance used to reduce fever.
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Antisera is serum containing immunoglobulins against specific antigens.
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The aorta is the main artery of the body from which all others derive; it arises from the left ventricle of the heart, arches over the top of the heart and descends in front of the backbone, giving off large and small branches and finally dividing to form the right and left iliac arteries in the legs.
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A dendrite is the slender branching process that arises from the dendrons of the nerve-cell body. A dendrite forms connections with the axons of other neurons and transmits nerve impulses. An apical dendrite is situated nearer the apex of a neuron.
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Apneic means related to or suffering from apnea, the transient cessation of breathing or a lack of oxygen.
- Apoptosis is a mechanism of cell death that results in the break down of the nucleus and fragmentation of DNA.
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The arcuate nucleus (arcuatus) is a cell group in the hypothalamus, located in the lowest part of the infundibulum adjacent to the median eminence; it is involved in neuroendocrine control through the release of releasing hormones and inhibitory hormones.
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An arrhythmia is any deviation from the normal rhythm of the heart.
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Arterial means relating to the arteries, blood vessels carrying blood away from the heart. All arteries except the pulmonary artery carry oxygenated blood.
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Arteriovenous means relating to both arteries and veins in general.
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The arteriovenous oxygen difference is the arterial oxygen content minus the central venous oxygen content.
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An artery is a blood vessel that carries oxygenated blood from the heart to the tissues and form part of the circulatory system. All arteries except the pulmonary artery carry oxygenated blood.
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An arthropod is any segmented invertebrate of the phylum Arthropoda, having joined legs and including the insects, arachnids (spiders), crustaceans, and myriapods.
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An artifact is any object made or modified by man.
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Ascomycetes, has a single nucleus, and reproduces either asexually by budding or fission, or sexually through spore formation.
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Ascorbic acid, an antioxidant, is an effective reducing agent that retards oxidation, the process by which substances combine with oxygen in the air at room temperature.
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Aseptic means a condition in which living pathogenic organisms are absent; a state of sterility.
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The aseptic technique is a manipulation of sterile instruments or culture media in such a way as to maintain sterility.
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ASI is the abbreviation for the Italian space agency, Agenzia Spaziale Italiana, which is headquartered in Rome, Italy.
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Aspergillus species is a common genus of fungi that contains many different species. All Aspergillus species form black, brown or green spores in form of a sphere on the tip of a hypha. A few species are pathogenic for humans, other mammals and birds.
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An assay is the analysis of a substance or mixture to determine its constituents or their level. In Life Sciences, it is also the estimation of strength of a drug or substance by comparing its effects in test animals to a reference standard.
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Atmosphere is a gaseous envelope surrounding a celestial body, especially that surrounding the Earth, which is retained in place by the force of gravity.
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Atmospheric relates to the environment or surroundings that have a physiological, physical or other influence.
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Atmospheric drag is a condition that occurs in the earth's atmosphere which can accelerate an orbiting body.
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Atmospheric physics is the science of the physics of the atmosphere, including the components and layers of the atmosphere.
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ATP (adenosine 5'-triphosphate) is a nucleotide that is of fundamental importance as a carrier of chemical energy in all living organisms. ATP can undergo hydrolysis, a reaction triggered by ATPase, which releases a large amount of energy that is used to fuel such biological processes as muscle contraction or the active transport of ions and molecules across cell membranes, or the synthesis of biomolecules.
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Atrial natriuretic factor (ANF) is a hormone-like substance present in the two atrial walls of the heart (especially numerous in the right atria). ANF can cause a three to ten times increase in renal (kidney) excretion of sodium when it is fully released into the circulating blood. Consequent to the loss of sodium is a slight decrease in the extracellular fluid volume and blood volume. Although its exact mechanism of action is unclear, it is believed that the ANF plays a role in the regulation of blood volume.
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Atrial natriuretic peptide (ANP), also called atrial natriuretic factor (ANF), is a hormone-like substance present in the two atrial walls of the heart (especially numerous in the right atria). ANP can cause a three to ten times increase in renal (kidney) excretion of sodium when it is fully released into the circulating blood. Consequent to the loss of sodium is a slight decrease in the extracellular fluid volume and blood volume. Although its exact mechanism of action is unclear, it is believed that the ANP plays a role in the regulation of blood volume.
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Atrioventricular dissociation is defined as the independent beating of the atria and ventricles.
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Atrophy is the wasting away of a normally developed organ or tissue due to degeneration of cells. This may occur through undernourishment, disuse, or aging. For example, muscle atrophy is the condition resulting from reduced muscle mass which is due to disuse of the muscles.
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Attenuation is the reduction of the disease-producing ability (virulence) of a microorganism. It can be achieved by chemical treatment, heating, drying, irradiation, by growing under adverse conditions, or by passing through another organism. Attenuated bacteria or viruses are used for some vaccines.
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Attitude is the nose up or nose down orientation of an aircraft's or spacecraft's axes relative to a reference line, plane or direction of motion.
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Audible means a noise or sound which is capable of being heard.
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An audiogram is the graphic record drawn by an audiometer, which charts the threshold of hearing at various frequencies against sound intensity in decibels.
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The auditory canal is the tube which extends from the opening of the ear to the tympanic membrane.
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An aurelia is a type of jellyfish known as "moon" jellyfish. They are found in the waters of the Atlantic Ocean and the Chesapeake Bay on the eastern coast of the North American continent.
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The auricle is the outer portion of the ear. It is made out of cartilage and its function is to channel sound waves into the ear tube.
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Autoflora refers to the microbial inhabitants of an individual.
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Autogenic refers to something that is produced independently of external influence or aid.
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Autogenic feedback training is a method that can be taught to people so that they can control motion sickness symptoms by using biofeedback techniques instead of drugs. The motion sickness is reduced when the person uses biofeedback to control normally involuntary processes, such as nausea, heart rate or body temperature.
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An autonomic function is a function that is independent or self-controlling.
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The autonomic nervous system is the part of the nervous system that supplies stimulation to the involuntary muscles, like the smooth and cardiac muscles, and to the glands. The autonomic nervous system is controlled principally by parts of the brain stem and the hypothalamus (a part of the brain).
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Autoradiography is an experimental technique in which a radioactive specimen is placed close to a photographic plate, so as to produce a record of the distribution of radioactivity in the specimen. The film is darkened by the ionizing radiation from radioactive parts of the sample. Autoradiography is used to study the distribution of particular substances in living tissues and cells. A radioactive isotope of the substance is introduced into the organism or tissue, which is killed, sectioned, and examined after enough time has elapsed for the isotope to be incorporated into the substance.
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Auxins are hormone-like chemicals that induce cellular growth in plants.
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Avionics is the science and technology of electronics applied to aeronautics and astronautics.
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The axilla is the armpit or an analogous part.
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Axillary means pertaining to the armpit.
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Axisymmetrical refers to like, or same, conditions on both sides of a body axis; a straight line about which a body or a geometric figure rotates.