| alveolar-arterial oxygen difference | The difference or gradient between the partial pressure of oxygen in the alveolar spaces and the arterial blood: P(A-a)02. Normally in young adults this value is less than 20 mm Hg. See: alveolar gas equation. (05 Mar 2000) |
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| atrioventricular gradient | The diastolic pressure difference between the atrium and ventricle. (05 Mar 2000) |
| magnetic field gradient | In magnetic resonance imaging, a magnetic field that varies with location, superimposed on the uniform field of the magnet, to alter the resonant frequency of nuclei and allow recovery of their spatial position. Synonym: field gradient. (05 Mar 2000) |
| ventricular gradient | The algebraic sum of (i.e., the net electrical difference between) the area enclosed within the QRS complex and that within the T wave in the electrocardiogram. (05 Mar 2000) |
| voltage gradient | <physiology> Literally, the electric field in a region, defined as the potential difference between two points divided by the distance between them. Used more loosely, the potential difference across a plasma membrane. (18 Nov 1997) |
| centrifugation, density gradient | Separation of particles according to density by employing a gradient of varying densities. at equilibrium each particle settles in the gradient at a point equal to its density. (12 Dec 1998) |
| cesium chloride gradient centrifugation | A type of density gradient centrifugation, a lab technique used to separate or purify nucleic acids. It involves putting cesium chloride and the nucleic acids into a centrifuge to be spun for hours or days. The cesium chloride forms a density gradient (highly dense at the bottom, thinnest at the top), and the different nucleic acids separate along the gradient according to their buoyancies in different densities. (09 Oct 1997) |
| gradient | <physics> Mathematical term for the operator which determines the magnitude and direction of the greatest rate-of-change of a given function with position. Similarly used to describe such a rate-of-change. For instance, at a given point on a hill, the slope of the hill in the steepest uphill direction is the gradient of the altitude function for the hill. (09 Oct 1997) |
| gradient elution | Elution in column chromatography in which a changing pH or ionic strength is used to separate substances. (05 Mar 2000) |
| gradient encoding | In magnetic resonance imaging, the technique of inducing a gradient in the magnetic field in the Y-axis to induce phase differences with location. Synonym: gradient encoding. (05 Mar 2000) |
| gradient perception | <cell biology> Problem faced by a cell that is to respond directionally to a gradient of, for example: a diffusible attractant chemical. In a spatial mechanism the cell would compare receptor occupancy at different sites on the cell surface, a temporal mechanism would involve comparison of concentrations at different times, the cell moving randomly between readings. In pseudospatial sensing, the cell would detect the gradient as a consequence of positive feedback to protrusive activity if receptor occupancy increased with time as the protrusion moved up gradient. Few cell types have been unambiguously shown to detect gradients. (18 Nov 1997) |
| mitral gradient | The diastolic pressure difference between the left atrium and left ventricle. (05 Mar 2000) |
| concentration gradient | <chemistry> A column of liquid in which the density varies continually with position, usually as a consequence of variation of concentration of a solute. Such gradients may be established by progressive mixing of solutions of different density as for example: sucrose gradients) or by centrifuge induced redistribution of solute (as for caesium chloride gradients). Density gradients are widely used for centrifugal and gravity induced separations of cells, organelles and macromolecules. The separations may exploit density differences between particles or primarily differences in size, in which latter case the function of the gradient is chiefly to stabilise the liquid column against mixing. (12 Jan 1998) |
| critical gradient | <botany> The maximum stable inclination of an unsupported slope under the most adverse conditions that it will likely experience, as determined by current engineering technology. (09 Oct 1997) |
| pseudospatial gradient sensing | <cell biology> Mechanism for sensing a gradient of a diffusible chemical in which the cell sends protrusions out at random, up gradient protrusions are stabilised by positive feedback (because receptor occupancy is rising with time) and others are transitory because of adaptation. Possibly the mechanism by which neutrophils sense chemotactic gradients. (18 Nov 1997) |