Science Glossary (A-F)

1-G (one-G) refers to the gravity force found on Earth.
15N-glycine is a radioactively labeled form of the amino acid glycine, which is found in protein. The nitrogen-15 (15N) isotope allows concentrations of glycine to be detected and measured in urine or saliva samples to evaluate protein metabolism.
2,3-diphosphoglycerate (2,3 DPG)
2,3-diphosphoglycerate (2,3 DPG; now known as 2,3-biphosphoglycerate) is an important regulator for the affinity of hemoglobin for oxygen. It synthesizes within red blood cells (RBCs). This synthesis represents a major reaction pathway for the consumption of glucose in RBCs. Note that when glucose is oxidized by this pathway the RBC loses the ability to gain 2 moles of adenosine triphosphate (ATP) from glycolytic oxidation of 1,3-biphosphoglycerate to 3-phosphoglycerate via the phosphoglycerate kinase reaction. The synthesis of 2,3-biphosphoglycerate in RBCs is critical for controlling hemoglobin affinity for oxygen. It plays a major role in making adjustments in oxygen delivery, over a period of several hours to one day. Thus, it sets the level of oxygen delivery, ensuring that delivery remains sufficient and almost constant despite modest variations in oxygen availability.
Absorptance is the ratio of absorbed to incident radiation.
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.
Acceleration is the rate of change of velocity with respect to time.
An accelerometer is a device which can measure acceleration, the rate of change of velocity with respect to time.
Acoustic means of or relating to sound, the sense of hearing, or the science of sound.
Acoustic dosimeter
An acoustic dosimeter is a device worn for determining the accumulated noise exposure with regard to level and time according to a pre-determined formula.
An actuator is a mechanical device used to move or control an object.
Adenosine Triphosphate (ATP)
Adenosine triphosphate (ATP) 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.
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.
Aerobic capacity
Aerobic capacity is the capacity of the respiratory and cardiovascular systems to deliver oxygen to working muscles.
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.
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.
Alkaline phosphatase
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.
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.
An alloy is composed of a mixture of two or more metals.
Amino acid
Amino acids are the building blocks 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.
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.
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.
By electrolytic action, anodyze is the process of coating or plating a metal (usually aluminum) with a protective material.
An anomaly is a deviation from the common rule; an irregularity.
Antidiuretic Hormone (ADH)
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, thus controlling the water content of the body.
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.
Antigenic means allergenic or having the properties of an antigen.
Antipyrine is a substance used to reduce fever.
Aperature is an adjustable opening in an optical instrument that limits the amount of light passing through a lens.
Apical means situated at the uppermost point.
Atmosphere is a gaseous envelope surrounding a celestial body, especially that surrounding the Earth, which is retained in place by the force of gravity.
Atmospheric drag
Atmospheric drag is a condition that occurs in the earth's atmosphere which can accelerate an orbiting body.
Atrial Natriuretic Peptide (ANP)
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.
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.
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.
Audible means a noise or sound which is capable of being heard.
Autonomic function
An autonomic function is a function that is independent or self-controlling.
Autonomic Nervous System (ANS)
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).
The axilla is the armpit or an analogous part.

B-cells are B-lymphocytes, one of two major types of lymphocytes (the other being T-lymphocytes). B-lymphocytes' primary function is the production of antibodies.
Bacteriorhodopsin is a carotenoid (naturally occurring pigment found mostly in plants) analogous to rhodopsin, the pigment of the animal eye, which functions in vision. Bacteriorhodopsin is able to absorb light and generate a proton gradient across the membrane of halobacterium (a microbe), leading to ATP synthesis without the involvement of chlorophyll.
Barium - ??
A baroreflex is a reflex triggered by the stimulation of a baroreceptor (a collection of sensory nerve endings in the wall of the heart auricles, vena cava, aortic arch and carotid sinuses that are specialized to monitor changes in blood pressure). The baroreflex acts to increase or decrease the blood pressure to maintain the necessary blood pressure within the body.
A baseline is a measurement that serves as a basis to which all following measurements are compared. An example: before exercise, your heart rate is measured. During exercise, your increased heart rate is measured and compared to your resting baseline measurement taken before exercise started.
Batch crystallization
Batch crystallization is a technique used for growing protein crystals by adding a precipitating solution directly to a protein solution and mixing them together. Once the precipitating solution is added, the mother liquor becomes supersaturated causing the proteins to solidify and crystallize.
Bioavailability is the degree to which an agent, such as a drug or nutrient, becomes available at the site of activity in the body.
Biochemical refers to the chemical reactions that occur within a living organism, such as the breakdown or manufacture of biological molecules by enzymes.
The bioreactor is a rotating wall vessel (RWV) developed by NASA and Synthecon, Inc. that is used to culture cells and tissues. By rotating the vessel, the cells remain in free fall which is similar to the microgravity environment.
The biosphere is the whole region of the Earth's surface, including the sea and the air, that is inhabited by living organisms.
Biotechnology refers to the industry that uses biological processes to make a product, such as a drug. An example is the use of yeast in the fermentation of beer.
Bone demineralization
Bone demineralization is the loss of minerals, including calcium and phosphorous, from the bone.
Bone density
Bone density is the mass per unit volume of bone under specified conditions of pressure and temperature.
Bone loss
Bone loss is the weakening and destruction of bone, particularly through demineralization. Demineralization is the loss of minerals, such as calcium from the bones or other mineralized structures of the body.
Brittle means easily broken, cracked or snapped.
Buoyancy is the capacity to float in a liquid medium.

Calcitonin (also called thyrocalcitonin or CT) is a hormone, produced by certain cells in the thyroid gland, that lowers the levels of calcium and phosphate in the blood. Calcitonin is believed to inhibit the resorption of bone.
Calcium (Ca)
Calcium is an element essential for the normal development and functioning of the body, typically present in the blood at a concentration of about 10mg/100ml. Calcium is an important constituent of bones and teeth and is essential for many metabolic processes, including nerve function, muscle contraction and blood clotting.
Calcium balance
Calcium balance is a measure of the intake and output of calcium from the body. The amount of free calcium in the body is measured by blood calcium levels. Higher than normal levels of calcium in the blood (hypercalcemia) may be an indication of many things, including an abnormal loss of bone calcium, caused by bone demineralization.
Calcium metabolism
Calcium metabolism is the distribution and utilization of calcium throughout the body, such as for bone formation and muscle contraction.
Calcium oxalate
Calcium oxalate is a chemical compound usually found as sediment in the urine and in urinary calculi. It can, if found in large quantities in the urine, indicate a higher than normal loss of calcium from the body, and thus indicate potential disease or abnormalities.
Calcium phosphate
Calcium phosphate is formed when free calcium and phosphate interact. In the human body, this interaction can happen when both minerals are excreted through the urinary tract, due to saturation of both minerals in the body, leading to the build-up of calculi and/or renal stones. Calcium phosphate is also referred to as calcium rock and its chemical formula is Ca3(PO4)2.
Candida albicans
Candida albicans is a species of yeast-like fungi normally a part of human gastrointestinal flora, but can become pathogenic when there is a disturbance in the balance of flora or in debilitation of the host (also called thrush fungus).
Carbon monoxide rebreathing method
Cardiac Output (CO)
Cardiac output (CO) is the amount of blood pumped by the heart in a unit period of time. The overall blood flow in the circulation of an adult person at rest is about 5000 ml per minute.
Cellulose is a polysaccharide carbohydrate composed of linked glucose units. It is the main consitutent of plant cell walls and is the most common organic compound on Earth.
The term cerebral refers to the portion of the brain that comprises mainly the central hemisphere (cerebral cortex and basal ganglia).
Chemical oxygen demand
Chloroform is a nonflammable, volatile liquid that was the first inhalation anesthetic to be discovered. It is a dangerous drug which can cause hypotension, myocardial and respiratory depression, cardiogenic shock, ventricular fibrillation, coma, and death if improper dosage is used. Delayed poisoning, even weeks after apparently complete recovery, can occur and serious vision or eye damage is frequently reported.
Chondritic means characterized by the presence of chondrules (rounded granules of cosmic origin often found embedded in meteoric stones and sometimes free in marine sediments).
A chondrocyte is a mature cartilage cell.
Chorioallantoic membrane
The chorioallantoic membrane is the extra-embryonic membrane formed by the fusion of the allantois with the serosa or false chorion. In mammals, it forms the fetal portion of the placenta; in avian embryos, it is fused with the shell.
Chromium is a metallic, non-toxic element, with period table symbol Cr. Chromium does not have any function in the human body.
Chromosomal refers to chromosomes. Chromosomes contain DNA, which transmits genetic information. They are located in the nucleus of both plant and animal cells. In humans there are 46 chromosomes.
A chromosome is a body located within the cell nucleus of both plant and animal cells (normally 46 in humans). Each chromosome is composed of deoxyribonucleic acid (DNA) and specialized protein molecules, which convey genetic information.
Circadian rhythm
Circadian rhythms, also called diurnal rhythms, are biological rhythms or variations that repeat with a cycle of about 24 hours.
A citrate is a compound of citric acid and a base; in the body it is involved in blood coagulation (clotting) and the synthesis of fatty acids.
Clearance is the removal of a substance from the blood via the kidneys. Kidney function can be tested by measuring the amount of a specific substance excreted in the urine in a given length of time.
Cohesion is the ability to stick together.
Cold pressor test
The cold pressor test is a test measuring the tendency to develop essential hypertension. One hand is placed in ice water. An excessive rise in the blood pressure or an unusual delay in the return of normal blood pressure when the hand is removed from the water is believed to indicate that the individual is at risk for hypertension.
Collagen is a protein that is the principal constituent of white fibrous connective tissue; it occurs in tendons, skin, bone, cartilage, and ligaments. It is relatively inelastic (not flexible) but has a high tensile strength (ability to resist forces of stretching).
Colloidal describes atoms or molecules dispersed in a gas, liquid or solid, which resist sedimentation (setting to the bottom), diffusion (spreading out), and filtration.
Combustion is the burning of a material, i.e., a chemical change accompanied by the production of heat and light.
Conductivity is a measure of the ability of a material to conduct electrical charge.
Contact angle
A contact angle is the angle between the solid surface (plate or vessel) and the liquid surface.
Convection is the transfer of heat by the circulation or movement of heated parts in a liquid or gas. Convection is also the circulatory motion that occurs in a fluid which is at a nonuniform (or varying) temperature caused by the variation of the density of liquid at different temperatures and the action of gravity.
A countermeasure is a measure or action taken in opposition to another. Several countermeasures are used to counteract the negative effects of space flight, including the performance of rigorous exercise to reduce the degeneration of muscles and bones caused by disuse during stays in microgravity.
Cratylia mollis
Cratylia mollis is a type of shrub found in South America.
Creatinine is a chemical substance excreted in the urine, which is derived from creatine and creatine phosphate. These substances serve to maintain adequate amounts of the substance adenosine triphosphate (ATP) which produces muscle contractions.
Critical current density
The critical current density represents the maximum current that can be transported by the film without losing superconductivity.
Critical transition temperature
The critical transition temperature represents the maximum temperature at which a material is superconducting.
Cystine is a chemical substance which naturally occurs as a deposit in the urine, and can form a calculus (hard mineral formation) when deposited in the kidney.
Cytokines are chemicals involved in growth and regulation. They also influence bone resorption (breakdown) and formation.
Cytomegalovirus is a group of herpetoviruses infecting man and other animals, many having special affinity for salivary glands, and causing enlargement of cells of various organs and development of characteristic inclusions in the cytoplasm or nucleus. Also known as visceral disease virus.

Damping is the dissipation of energy with time or distance. The term is generally applied to the attenuation of sound in a structure owing to the internal sound-dissipative properties of the structure or to the addition of sound-dissipative materials.
Deoxyribonucleic Acid (DNA)
Deoxyribonucleic acid (DNA) is a complex molecule found in the chromosomes of almost all organisms which acts as the chemical storage for primary genetic material. DNA contains the chemical "code" which allows traits and inherited characteristics to be passed down from organism to organism.
Deposition is the precipitation of mineral matter from solution, such as the deposition of agate, vein quartz, etc.
The Dewar is a thermos-like container used to store protein samples and keep them frozen until the liquid nitrogen thaws.
Dialysis is a form of diffusion, i.e., a form of filtration to separate a crystalloid from colloid substance in a solution by interposing a semi-permeable membrane between the solution and water. The crystalloid substances pass through the membrane into the water on the other side, the colloids do not.
The diencephalon is the portion of the embryonic brain that develops into the thalamus, hypothalamus, and associated structures, all of which make up the diencephalon (hindbrain) in the adult. It includes structures important in the visual pathway. Some sources consider the adult diencephalon to be part of the brainstem.
Diffusion generally refers to the spreading out or dispersing of a material. Chemical diffusion is a passive process in which there is a net or greater movement of molecules or ions from a region of high concentration to a region of low concentration until equilibrium is reached.
Dilatancy is an increasing viscosity with increasing rate of shear accompanied by volumetric expansion.
Dioctyl phthatate - ??
Distal means anatomically situated away from the origin or point of attachment, or from the middle line of the body. It is specifically applied to the extremity or distant part of a limb or organ. For example, the fingers are the most distal portion of the arm in relation to the torso.
Diurnal means pertaining to or occurring in the daytime; opposite of nocturnal. Diurnal also means repeating once each 24 hours.
DNA fingerprinting
DNA fingerprinting is a method used to identify individuals within a species. The DNA fingerprint itself is the individual-specific autoradiographic banding pattern (shown by electrophresis) that is produced when DNA is digested with a restriction endonuclease.
Dynamic Random Access Memory
Dual Energy X-ray Absorptiometry (DEXA)
Dual Energy X-ray Absorptiometry (DEXA) provides accurate measurements of whole and regional body composition (fat, bone and muscle tissue).
Ductile is the ability of a substance to be hammered thin.
Dysrhythmia is any abnormality in the rate, regularity or sequence of heart activity.

Electro-oculography (EOG)
Electro-oculography (EOG) is the method of placing electrodes on the skin around the eye to record eye movements. The electrodes measure the small changes in the electrical potentials in the skin as the eyeball moves.
An electrolyte is an element or compound that, when dissolved or melted in water or other solvent, dissociates into ions and is able to conduct electric current. Electrolyte concentrations differ between the blood plasma, interstitial fluid and cell fluid, which affects the movement of substances between these fluids. Proper quantities of principal electrolytes and balance among them are critical to normal metabolism and function.
Electromagnetic interference
Electromagnetic interference (EMI) is any electromagnetic disturbance that interrupts, obstructs, or otherwise degrades or limits the effective performance of electronics/electrical equipment. It can be induced intentionally, as in some forms of electronic warfare, or unintentionally, as a result of spurious emissions and responses, intermodulation products, and the like.
Electromyographic (EMG)
Electron spectroscopy
Ellipsometry is the measurement of the change in ellipticity (the quality of asymmetrical intensity distribution in a laser beam, as opposed to a circular distribution) of an optically polarized light beam after reflection from a surface in a particular manner.
An embryo is an animal at the early stage of development, before birth.
Embryogenesis is the formation and development of an embryo.
Emittance is a rating of the ability of a material to give off heat as radiant energy. The emissivity of a material is expressed as a fraction. Emittance values range from 0.05 for brightly polished metals to 0.96 for flat black paint.
Endocrine means secreting internally, most commonly into systemic circulation.
Endocrine gland
The endocrine glands manufacture one or more hormones and secrete them directly into the bloodstream. Endocrine glands include the pituitary, thyroid, parathyroid, adrenal, ovary, testis, placenta and part of the pancreas.
Endothelial cell
Endothelial cells are the inside cellular lining of a tissue.
Enzyme Linked Immunosorbent Assay (ELISA)
Enzyme Linked Immunosorbent Assay (ELISA) is used for diagnosis of specific infectious diseases. An enzyme is used as the indicator system; when the enzyme and the antigen-antibody complex bind, a color indicator or other easily recognizable sign occurs.
Epstein-Barr virus
The Epstein-Barr virus is a herpesvirus that causes infectious mononucleosis (mono). It is also found in cell cultures of Burkitt's lymphoma and is associated with nasopharyngeal carcinoma.
An ergometer is a rotary pedal device (i.e., static exercise bicycle) that provides a calibrated, or specific, resistance. The force required to overcome the resistance is measured as work.
An erythrocyte is more commonly known as a red blood cell, which is the most numerous type of blood cell. Erythrocytes contain the red pigment hemoglobin and are responsible for oxygen transport. In humans, the number of erythrocytes in the blood varies between 4.5 and 5.5 million per cubic millimeter. They survive for about four months and are then destroyed in the spleen and liver.
Erythropoiesis is the process of red blood cell production, which normally occurs in the blood-forming tissue of the bone marrow.
Erythropoietin is a hormone secreted by certain cells in the kidney in response to a reduction in the amount of oxygen reaching the tissues; it stimulates red blood cell production.
Escherichia coli
Escherichia coli is a strain of harmless bacteria that live in the intestines of healthy humans and animals. However, the O157:H7 strain, transmitted through improperly prepared infected meat or contact with infected feces, produces a powerful toxin that can cause severe illness.
Esterase is a generic term for enzymes that catalyze the hydrolysis of esters.
Ethylene glycol - ??
Excretion is the transport and expulsion of waste products such as urine or carbon dioxide. It also refers to the release of hormones or protein products from cells or tissues.
Exercise capacity
Exercise capacity is the maximum ability of the body to take up and use oxygen to do work. This is often reported as the maximum number of liters of oxygen that the body can use in a minute.
Extracellular fluid
Extracellular fluid is the fluid which is inside the body, but outside the cells that are within the body.
Extravehicular Activity (EVA)
An extravehicular activity, or EVA, is any activity that occurs external to the spacecraft requiring the crewmember to wear a life support suit.

Factor D
Factor D is an enzyme important in the activation of the complement system. This complicated system of enzymes protects humans by killing microorganisms and infected cells.
Ferritin is an iron-protein complex and is one of the forms in which iron is stored in the tissues of the intestine, spleen, and liver.
Flora are microorganisms that live on or within a body to compete with disease-producing microorganisms and provide a natural immunity against certain infections.
A floret is a small flower or cluster of flower buds, such as in a head of cauliflower.
Flow cytometer
Fluence refers to the ease with which particles flow.
Fluid shift
Fluid shift refers to the shift of fluids from the lower to the upper body upon exposure to or recovery from microgravity. This phenomenon also occurs to a lesser extent during bed rest or exposure to lower body negative pressure. It may also refer to fluid transfer between intracellular and extracellular compartments.
Forcing function

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