| down-regulation | <physiology> Development of a refractory or tolerant state consequent upon repeated administration of a pharmacologically or physiologically active substance. It is the process that decreases ligand and receptor interactions or reduces the responsiveness of a cell to a stimulus following first exposure. This is often accompanied by an initial decrease in affinity of receptors for the agent and a subsequent reduction in the number of available receptors expressed on the surface which can result from internalisation of the ligand:receptor complex or from decreased expression of the receptor. Classically the concept referred to hormone receptors but contemporary usage includes other cell surface receptors. (03 Jul 1999) |
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| target regulation | <physiology> General term for an interaction between neurons and their targets by which target derived signals influence the differentiation of the innervating neurons. (18 Nov 1997) |
| enzyme regulation | <biochemistry> Control of the rate of a reaction catalyzed by an enzyme by some effector (e.g., inhibitors or activators) or by alteration of some condition (e.g., pH or ionic strength). (05 Mar 2000) |
| facility regulation and control | Formal voluntary or governmental procedures and standards required of hospitals and health or other facilities to improve operating efficiency, and for the protection of the consumer. (12 Dec 1998) |
| feedback regulation | <physiology> Control mechanism that uses the consequences of a process to regulate the rate at which the process occurs: if, for example: the products of a reaction inhibit the reaction from proceeding (or slow down the rate of the reaction), then there is negative feedback, something that is very common in metabolic pathways. Positive feedback is liable to lead to exponential increase and may be explosively dangerous in some cases. Other examples are the action of voltage dependent sodium channels in generating action potentials and the activation of blood clotting factors V and VIII by thrombin. Without damping, feedback can lead to resonance (hunting) and oscillation in the system. (18 Nov 1997) |
| up-regulation | Opposite of down-regulation. (05 Mar 2000) |
| up-regulation (physiology) | Process that increases ligand/receptor interactions due to an increase in the number of available receptors. (12 Dec 1998) |
| bone scan: falsely negative metastases | <radiology> Anaplastic tumours, reticulum cell sarcoma, renal cell carcinoma, thyroid carcinoma, histiocytosis, neuroblastoma, multiple myeloma (positive scan usually due to recent or impending fracture) (12 Dec 1998) |
| ventilators, negative-pressure | Body ventilators that assist ventilation by applying intermittent subatmospheric pressure around the thorax, abdomen, or airway and periodically expand the chest wall and inflate the lungs. They are relatively simple to operate and do not require tracheostomy. These devices include the tank ventilators ("iron lung"), portalung, pneumowrap, and chest cuirass ("tortoise shell"). (12 Dec 1998) |
| gram-negative | <microbiology> A common class of bacteria normally found in the gastrointestinal tract that can be responsible for disease in man (sepsis). Bacteria are considered to be gram-negative because of their characteristic staining properties under the microscope, where they either do not stain or are decolourised by alcohol during Gram's method of staining. This is a primary characteristic of bacteria that have a cell wall composed of a thin layer of peptidoglycan covered by an outer membrane of lipoprotein and lipopolysaccharide containing endotoxin. The gram staining characteristics of bacteria have resulted in an important classification system for the identification of bacteria. See: gram-positive (06 Oct 1997) |
| gram-negative aerobic bacteria | <microbiology> A large group of aerobic bacteria which show up as pink (negative) when treated by the gram-staining method. (12 Dec 1998) |
| gram-negative aerobic rods and cocci | <microbiology> A group of gram-negative bacteria consisting of rod- and coccus-shaped cells. They are both aerobic (able to grow under an air atmosphere) and microaerophilic (grow better in low concentrations of oxygen) under nitrogen-fixing conditions but, when supplied with a source of fixed nitrogen, they grow as aerobes. (12 Dec 1998) |
| gram-negative anaerobic bacteria | <microbiology> A large group of anaerobic bacteria which show up as pink (negative) when treated by the gram-staining method. (12 Dec 1998) |
| gram-negative anaerobic cocci | <microbiology> A group of anaerobic coccoid bacteria that show up as pink (negative) when treated by the gram-staining method. (12 Dec 1998) |
| gram-negative anaerobic straight, curved, and helical rods | <microbiology> A group of anaerobic, rod-shaped bacteria that show up as pink (negative) when treated by the gram-staining method. (12 Dec 1998) |