| MPD | main pancreatic duct; maximum permissible dose; mean population doubling; membrane potential differe... |
|---|---|
| PDL | pancreatic duct ligation; periodontal ligament; poorly differentiated lymphocyte; population doublin... |
| PDT | photodynamic therapy; population doubling time |
| Pop | popliteal; population |
| POPLINE | Population Information Online |
| diffusion | The process of becoming diffused or widely spread, the spontaneous movement of molecules or other particles in solution, owing to their random thermal motion, to reach a uniform concentration throughout the solvent, a process requiring no addition of energy to the system. (18 Nov 1997) |
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| diffusion anoxia | Diffusion hypoxia severe enough to result in the absence of oxygen in alveolar gas. (05 Mar 2000) |
| diffusion chambers, culture | Devices used in a technique by which cells or tissues are grown in vitro or, by implantation, in vivo within chambers permeable to diffusion of solutes across the chamber walls. The chambers are used for studies of drug effects, osmotic responses, cytogenic and immunologic phenomena, metabolism, etc., and include tissue cages. (12 Dec 1998) |
| diffusion constant | For the translational diffusion of solutes, diffusion is described by Fick's First Law, that states that the amount of a substance crossing a given area is proportional to the spatial gradient of concentration and the diffusion constant (D), that is related to molecular size and shape. A useful derived relationship is that the mean square distance moved by molecules in time t is 6Dt. (18 Nov 1997) |
| diffusion hypoxia | Abrupt transient decrease in alveolar oxygen tension when room air is inhaled at the conclusion of a nitrous oxide anaesthesia, because nitrous oxide diffusing out of the blood dilutes the alveolar oxygen. (05 Mar 2000) |
| diffusion limitation | The boundary layer hypothesis, that the proliferation of cells in culture is limited by the rate at which some essential component (almost certainly a growth factor) diffuses from the bulk medium into the layer immediately adjacent to the plasma membrane. By spreading out, a cell obtains a supra threshold level of the factor and can divide, if unable to spread (because of crowding or poor adhesion) then the cell will remain in the G0 stage of the cell cycle. (18 Nov 1997) |
| diffusion method | A method for the study of bacterial enzymes in which agar is mixed with the material (e.g., starch or milk) which is to serve as an indicator of the enzyme action and is inoculated and plated; if the bacteria produce enzymes digesting the admixed material, there will be a zone of clearing in the medium about each colony. Synonym: diffusion method. (05 Mar 2000) |
| diffusion of innovation | The broad dissemination of new ideas, procedures, techniques, materials, and devices and the degree to which these are accepted and used. (12 Dec 1998) |
| diffusion potential | Potential arising from different rates of diffusion of ions at the interface of two dissimilar fluids, a junction potential. (18 Nov 1997) |
| diffusion respiration | Maintenance of oxygenation during apnea by intratracheal insufflation of oxygen at high flow rates. Synonym: apneic oxygenation. (05 Mar 2000) |
| diffusion shell | A small vessel made of a semipermeable membrane through which peptone, but not serum albumin, can pass; used in performing the Abderhalden test. (05 Mar 2000) |
| facilitated diffusion | <physiology> A process by which substances are conveyed across cell membranes faster than would be possible by diffusion alone. This is generally achieved by proteins that provide a hydrophilic environment for polar molecules throughout their passage through the plasma membrane, acting as either shuttles or pores. See: symport, antiport, uniport. (18 Nov 1997) |
| fick's law of diffusion | The principle that a substance put into solution will tend to diffuse towards constant concentration throughout the solution. (09 Oct 1997) |
| Fick's laws of diffusion | The direction of movement of solutes by diffusion is always from a higher to a lower concentration and the diffusive flux JA of solute A across a plane at x is proportional to the concentration gradient of A at x; i.e., JA = -D(CA/x), the increase of concentration of solute A with time, CA/t, is directly proportional to the change in the concentration gradient, i.e., CA/t = D(fl2/x2). (05 Mar 2000) |
| lateral diffusion | Diffusion in two dimensions, usually referring to movement in the plane of the membrane, such as the motion of fluorescently labelled lipids or proteins measured by the technique of fluorescent recovery after photobleaching (FRAP). (18 Nov 1997) |