| PNS | paraneoplastic syndrome; parasympathetic nervous system; partial nonprogressive stroke; peripheral n... |
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| PPS | Personal Preference Scale; physician, patient and society [course]; polyvalent pneumococcal polysacc... |
| RAS | rapid atrial stimulation; recurrent aphthous stomatitis; reflex activating stimulus; reliability, av... |
| SCS | Saethre-Chotzen syndrome; shared computer system; silicon-controlled switch; Society of Clinical Sur... |
| SIS | semantic indexing system; serotinin irritation syndrome; simian sarcoma; simulator-induced syndrome;... |
| portal system | A system of vessels in which blood, after passing through one capillary bed, is conveyed through a second set of capillaries before it returns to the systemic circulation. It pertains especially to the hepatic portal system. (12 Dec 1998) |
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| haematopoietic system | The blood-making organs; in the embryo at different ages these are the yolk sac, liver, thymus, spleen, lymph nodes, and bone marrow; after birth they are principally the bone marrow, spleen, thymus, and lymph nodes. (05 Mar 2000) |
| haemolytic system | <haematology> A haemolytic system is composed of red blood cells covered with antibodies which are genetically identical to the surface proteins (antigens) of the red blood cells. It is used to measure how much complement is left after a round of complement fixation. (09 Oct 1997) |
| cytochrome system | The mitochondrial electron transport chain. (18 Nov 1997) |
| pressoreceptor system | The pressoreceptive areas which with their afferent fibres and connections with the autonomic system react to a rise in arterial blood pressure and serve to buffer it by inhibiting the heart rate and vascular tone. See: baroreceptor. (05 Mar 2000) |
| haversian system | <anatomy> The basic unit of structure of compact bone, comprising a haversian canal and its concentrically arranged lamellae, of which there may be 4 to 20, each 3 to 7 microns thick, in a single haversian system. A haversian canal is a freely anastomosing channel in compact bone containing blood vessels and running longitudinally in the centre of haversian systems of compact osseous tissue. It was originally described by Clopton Havers, an english physician, in 1691. (12 Dec 1998) |
| heart conduction system | An impulse-conducting system composed of modified cardiac muscle and having the power of spontaneous rhythmicity and conduction more highly developed than the rest of the heart. (12 Dec 1998) |
| projection system | The system of axons carrying stimuli from one portion of the nervous system to other portions. (05 Mar 2000) |
| hepatic portal system | A venous portal system in which the portal vein receives blood via its tributaries from the capillaries of most of the abdominal viscera and drains it into the hepatic sinusoids. (05 Mar 2000) |
| properdin system | An immunological system that is the alternative pathway for complement, composed of several distinct proteins that react in a serial manner and activate C3 (third component of complement), seemingly without utilizing components C1, C4, and C2; in addition to properdin, the system includes properdin factors A (native C3), B (C3 proactivator), D (C3 proactivator convertase), and perhaps at least one other, E; the system can be activated, in the absence of specific antibody, by bacterial endotoxins, by a variety of polysaccharides and lipopolysaccharides, and by a component of cobra venom. (05 Mar 2000) |
| prospective payment system | A system wherein reimbursement rates are set, for a given period of time, prior to the circumstances giving rise to actual reimbursement claims. (12 Dec 1998) |
| Schlieren system | <microscopy> A system for enhancing path length differences, refractive index differences in transparent media, or height differences for light reflected from surfaces. (05 Aug 1998) |
| heterogeneous system | In chemistry, a system that contains various distinct and mechanically separable parts or phases; e.g., a suspension or an emulsion. (05 Mar 2000) |
| hexaxial reference system | The figure resulting if the lines of derivation of the unipolar limb leads of the electrocardiogram are added to the triaxial reference system. (05 Mar 2000) |
| His-Tawara system | The complex system of interlacing Purkinje fibres within the ventricular myocardium. See: conducting system of heart. (05 Mar 2000) |