| 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) |
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| 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) |
| second signaling system | <psychology> Pavlovian term for speech in which words are considered to be the second signals capable of producing conditioned responses. (05 Mar 2000) |
| pulmonary branch of autonomic nervous system | Pulmonary branches of cardiac plexuses and cardiaopulmonary splanchnic nerves. Synonym: rami pulmonales systematis autonomici. (05 Mar 2000) |
| homogeneous system | In chemistry, a system whose parts cannot be mechanically separated, and is therefore uniform throughout and possesses in every part identically physical properties; e.g., a solution of sodium chloride in water. (05 Mar 2000) |
| Purkinje system | <cardiology, physiology> Terminal ramifications in the ventricles of the specialised conducting system of the heart. (05 Mar 2000) |
| sensory system agents | Drugs that act on neuronal sensory receptors resulting in an increase, decrease, or modification of afferent nerve activity. (12 Dec 1998) |