Deactivate means to render inactive or ineffective.
Dead space is the area in the respiratory passages in which no gas exchange takes place.
Deafferentation is a loss of the sensory nerve fibers, or their impulses, from a portion of the body.
Debris are the scattered remains of something broken or destroyed.
Decarboxylase is an enzyme that removes a molecule of carbon dioxide from a carboxylic group (e.g. from an a-amino acid, converting it into an amine).
Decompression is the removal of pressure.
Deconditioning is a term used to describe a decrease in muscle strength or cardiovascular responses.
Decontamination means to remove the contaminants or dangerous agents from something, e.g. buildings, clothing, the ground, etc.
A defibrillator is a device which administers a controlled electric shock to restore normal heart rhythm in cases of cardiac arrest due to ventricular fibrillation (chaotic and abnormal pumping of the heart which does not allow the heart to pump blood effectively and is due to a disease or medical complication). The defibrillator administers the shock either through electrodes placed externally on the chest wall over the heart or directly to the heart after the chest has been opened surgically.
Dehydration is the loss of deficiency of water in body tissues. The condition may result from inadequate water intake and/or from excessive removal of water from the body; for example, by sweating, vomiting or diarrhea.
Dehydroepiandrosterone (DHEA) is a weakly androgenic steroid secreted largely by the adrenal cortex, but also by the testes. It is one of the principal components of urinary 17-ketosteroids.
Demineralization is the loss of minerals, such as calcium and phosphorus, from the bone.
Denitrogenation is the elimination of nitrogen from the lungs and body tissues by breathing gases devoid of nitrogen.
A densitometer is an electronic instrument used to measure the density, or degree of darkening, of a photographic film or plate, a liquid or material deposited on a chromatographic plate or electrophoresis medium, by photometrically recording its transparency.
Densitometry is the measurement of the density or compactness of bone. It is also an indirect method of determining body composition; using this method, percentage of body fat is computed from bone density (the ratio of body weight to body volume).
In the process of bone resorption, the type I collagen cross linking molecule deoxypyridinoline (Dpd) is released into the circulation and cleared by the kidney. Dpd in urine can be measured as a specific marker of bone resorption.
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.
To deploy is to station or distribute systematically over an area (in preparation for operation or activity).
Dermatitis is the inflammation of skin.
A dermatophyte is a fungus that causes infections of the skin, hair and/or nails, i.e., keratinized tissue.
Desiccation means dehydration.
Detailed Supplementary Objective (DSO)
A Detailed Supplementary Objective (DSO) is a NASA-sponsored investigation performed voluntarily by Space Shuttle crewmembers, who serve as the test subjects. These studies are designed to require minimal crew time, power and stowage. Biomedical DSOs focus on operational concerns, including space motion sickness, cardiovascular deconditioning, muscle loss, changes in coordination and balance strategies, radiation exposure, pharmacokinetics and changes in the body's biochemistry. Key hardware and procedures have been tested and verified as DSOs prior to use in support of more costly, complex life sciences investigations. Data may be collected before, during and after flight, and usually subjects from more than one mission participate in each DSO. Some DSOs were also part of the Extended Duration Orbiter Medical Project.
Deuterium is an isotope of hydrogen (same number of protons in the nucleus, but a different number of neutrons).
Development Test Objective (DTO)
At the beginning of the Shuttle Program, the Space Transportation System (STS) Program Office established a procedure for testing and refining Orbiter and subsystem performance capabilities, and for evaluating new hardware and procedures. Procedures involving the Orbiter, its subsystems, and its support equipment were designated Development Test Objectives (DTOs). All other operationally relevant procedures were classified as DSOs.
Developmental biology research is concerned with the influences of gravity and microgravity on reproduction, differentiation, growth, development, life span, aging and subsequent generations of animals.
Dexamethasone is a glucocorticoid which is prescribed in the treatment of inflammatory conditions.
Dexterity is skill in using the hands or body.
Dextroamphetamine is a form of amphetamine, a drug that stimulates the central and peripheral nervous systems.
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.
Dialyze means to prepare by diffusion through a semipermeable membrane.
A diaphragm is a thin dome-shaped skeletal muscle that separates the thoracic and abdominal cavities. The diaphragm plays an important role in breathing: it contracts with each inspiration, becoming flattened downward and increasing the volume of the thoracic cavity so that air is drawn into the respiratory tract, and then, with expiration, it relaxes and is restored to its dome shape.
Diastole is the phase of the heart during which the heart muscle relaxes, causing blood to fill the heart chambers.
Diastolic blood pressure
Diastolic blood pressure is the blood pressure measured during diastole, or the dilation of the heart cavities, during which they fill with blood. It is the force exerted by blood on arterial walls, and the lowest blood pressure measured in the large arteries is about 80 mm Hg under normal conditions for a young, adult male.
Didactic means pertaining to instruction or teaching.
Differential is a kind of analysis that allows for the identification and distinguishing of various kinds of cells.
A differential count is an estimate of the percentage of white blood cell types which make up the total white blood cell count.
Differentiation, in embryology, is the process in embryonic development during which unspecialized cells or tissues become specialized for particular functions. Differentiation, in oncology, is the degree of similarity or difference of tumor cells to the structure of the organ from which the tumor arose.
The diffusing capacity is the volume of a gas that diffuses through a membrane each minute for a pressure difference of 1mm Hg.
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.
The diffusion coefficient is a numerical measure of the diffusion property that is constant for a specified system. Diffusion 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.
Digital is a term for a transmission mode in which data is measured in discrete intervals. Digital electronics systems measure voltage being turned on an off through a series of numbers using only 1s and 0s.
Dilation is the physiologic, pathologic, or artificial enlargement of a cavity, canal, blood vessel or opening.
A dilution series is a method for counting the number of viable cells in a suspension; a sample is diluted to the point where an aliquot, when plated, yields a countable number of separate colonies.
Dimethyl sulfoxide (DMSO)
Dimethyl sulfoxide (DMSO) is a penetrating solvent, that enhances the absorption of therapeutic agents and has been proposed as an effective analgesic and anti-inflammatory agent in arthritis and bursitis.
A diphtheroid is a bacterium (especially genus Corynebacterium) that resembles the bacterium of diphtheria but does not produce diphtheria toxin.
Diploid means denoting the state of a cell containing twice the normal gametic number of chromosomes, one member of each chromosome pair derived from the father and one from the mother; the normal chromosome complement of somatic cells.
Dipyridamole is a coronary vasodilator which is prescribed for the long term treatment of angina.
A discocyte is a red blood cell that is in the normal, biconcave disc shape.
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.
Diuresis is the increased secretion of urine by the kidneys. This normally follows the drinking of more fluid than the body requires, but it can be stimulated by the administration of a drug called diuretic or by the fluid shift which occurs in microgravity.
Diurnal means pertaining to or occurring in the daytime; opposite of nocturnal. Diurnal also means repeating once each 24 hours.
The acronym DLCO stands for the diffusing capacity of the lung.
The acronym DM stands for the diffusing capacity of the alveolar capillary membrane, the outer membrane of the smallest blood vessels, called capillaries, in the lung.
DMSO is the abbreviation for dimethyl sulfoxide, a penetrating solvent, that enhances the absorption of therapeutic agents and has been proposed as an effective analgesic and anti-inflammatory agent in arthritis and bursitis.
Deoxyribonucleic acid (DNA) is a complex molecule found in the chromosomes of almost all organisms which acts as the primary genetic material; the part of the cell nucleus that is the repository of hereditary characteristics.
Dorsal means relating to or situated at or close to the back of the body or to the posterior part of an organ.
Dorsiflexion is the backward flexion of the foot, toes, hand or fingers, (bending toward the upper surface).
The dorsiflexor is a muscle which turns the foot, toes, hands or fingers upward towards the upper surface.
The term dorsomedial is used in medicine to refer to the central, back region of the body area being discussed. The term comes from the Latin dorso (posterior or back) and medial (relating to the middle or center). Thus the term "dorsomedial aspect of the thigh" means centrally located behind the thigh.
A dosimeter is a device used to record the amount of radiation received by workers from X-rays or other radiation, usually consisting of a small piece of photographic film in a holder attached to the clothing. At regular intervals the film is examined to determine the amount of radiation it (and therefore, the wearer) has received.
Dosimetry is the accurate determination of dosage, i.e., the quantity of radiation received over a given period of time.
Doubly labeled water
Doubly labeled water is a method of measuring metabolism by using two stable, non-radioactive chemical isotopes: deuterium (2H) and oxygen (18O). This method has the advantage that the two metabolic processes in the body involving hydrogen and oxygen can be monitored simultaneously. Deuterium leaves the human body in urine, while the labeled oxygen is found in urine and exhaled CO2. The difference between the two isotopes found in the urine sample is equal to the rate of CO2 production, which indicates energy consumption.
Drosophila are a species of fruit flies. Drosophila are often used in genetic research because the larvae possess large chromosomes in their salivary glands. Fruit flies have a short life cycle and produce a large number of offspring, which makes them an ideal species for scientific study.
Dual Energy X-ray Absorptiometry (DEXA)
Dual Energy X-ray Absorptiometry (DEXA) provides accurate measurements of whole and regional body composition (fat, lean and muscle tissue).
Dysbarism is a reaction to sudden change in ambient pressure, such as rapid exposure to the lower atmospheric pressures of high altitudes. It is marked by symptoms similar to those of decompression sickness.
A dysfunction is an abnormal function, that is either diseased, faulty or bad.
Dysrhythmia is any abnormality in the rate, regularity or sequence of heart activity.