- 1. [TA] A consistent and complex whole made up of correlated and semiindependent parts. A complex of functionally related anatomic structures. 2. The entire organism seen as a complex organization of parts. 3. Any complex of structures anatomically related ( e.g., vascular s.) or functionally related ( e.g., digestive s.). 4. A scheme of medical theory. SEE ALSO: apparatus, classification. 5. S. followed by one or more letters denotes specific amino acid transporters; s. N is a sodium-dependent transporter specific for amino acid s such as l-glutamine, l-asparagine, and l-histidine; s. y+ is a sodium-independent transporter of cationic amino acid s. SYN: systema [TA]. [G. systema, an organized whole]- absolute s. of units a s. based on absolute units accepted as being fundamental (length, mass, time) and from which other units (force, energy or work, power) are derived; such systems in common use are the foot-pound-second, centimeter-gram-second, and meter-kilogram-second systems.- alimentary s. [TA] the digestive tract from the mouth to the anus with all its associated glands and organs. SYN: systema digestorium [TA], alimentary apparatus, apparatus digestorius, digestive apparatus, digestive s., systema alimentarium.- anterolateral s. a composite bundle of fibers, located in the ventrolateral part of the lateral funiculus, containing spinothalamic, spinohypothalamic, spinoreticular, and spinomesencephalic (spinotectal, spinal to periaqueductal grey, etc.) fibers; occupies the combined areas of the spinal white matter historically divided into anterior and lateral spinothalamic tracts; located in white matter ventral to the denticulate ligament, hence the anatomical basis for the anterolateral cordotomy; concerned with the transmission of nociceptive and thermal information and with crude (nondiscriminative) touch. SEE ALSO: spinothalamic tract. SYN: anterolateral tract, tractus anterolaterales.- association s. groups or tracts of nerve fibers interconnecting different regions of one and the same major subdivision of the central nervous s., such as the various areas of the cerebral cortex or the various segments of the spinal cord.- Bethesda s. a s. for reporting cervical or vaginal cytologic findings and diagnoses. SYN: Bethesda classification. [Bethesda, Maryland, site of NIH] George Papanicolaou divided cytologic findings on stained cervical smears into five classes, ranging from I (normal) to V (carcinoma). Classes II–IV represented increasing degrees of premalignant squamous cellular atypia. Later workers modified the s. by introducing the terms dysplasia (mild, moderate, severe) and cervical intraepithelial neoplasia (CIN) (grades 1–3). Pap smear findings reported according to this nomenclature showed poor reproducibility between observers and even between separate readings by the same observer. In addition, there was little correlation between diagnostic categories and treatment options. In 1988 the National Cancer Institute sponsored a workshop in Bethesda, Maryland, to establish a more useful s.. The Bethesda s. was first used in 1991 and has now become standard throughout the world. This recording s. replaces numerical designations with descriptive diagnoses of cellular changes. The accompanying table compares the Bethesda s. with earlier classifications. The standard format for reporting cervical cytology findings according to the Bethesda s. comprises three elements: 1) a statement of the adequacy of the specimen (satisfactory, unsatisfactory, or satisfactory but limited by, e.g., absence of endocervical cells); 2) general categorization (within normal limits, benign cellular changes, or epithelial cell abnormality); and 3) descriptive diagnosis, elaborating on the general categorization and including mention of all significant abnormalities, as well as of the patient's hormonal status (when vaginal cells are present in the smear). Benign cellular changes include those due to infection (Candida, Trichomonas, herpes simplex), atrophy, radiation therapy, or the presence of an IUD. Epithelial cell abnormalities may involve either squamous or glandular cells. Abnormal squamous cells of undetermined significance (ASCUS) show cellular atypia but not clear evidence of premalignant change. About 20% of women with ASCUS eventually develop squamous intraepithelial lesions or invasive carcinoma. Squamous cell changes formerly called mild dysplasia or CIN 1 (including cellular atypia characteristic of human papillomavirus infection) are now designated low-grade squamous intraepithelial lesion. The category of high-grade squamous intraepithelial lesion encompasses what were formerly called moderate and severe dysplasia or CIN 2 and CIN 3. Abnormalities of glandular cells are similarly categorized.- cardiovascular s. [TA] the heart and blood vessel s considered as a whole. SYN: systema cardiovasculare [TA], blood-vascular s..- centimeter-gram-second s. (CGS, cgs) the scientific s. of expressing the fundamental physical units of length, mass, and time, and those units derived from them, in centimeters, grams, and seconds; currently being replaced by the International S. of Units based on the meter, kilogram, and second.- central nervous s. (CNS) [TA] the brain and the spinal cord. SYN: pars centralis systematis nervosi [TA], systema nervosum centrale.- chromaffin s. the cells of the body that stain with chromium salts and occur in the medullary portion of the adrenal body, paraganglia, and in relation to certain sympathetic nerves.- closed s. a s. in which there is no exchange of material, energy, or information with the environment.- colloid s. a combination of the two phases, internal and external, of a colloid solution; the various systems are: gas + liquid (foam); gas + solid (meerschaum); liquid + gas (fog); solid + gas (smoke); solid + liquid (sol); liquid + solid (gel); liquid + liquid (emulsion); solid + solid (colored glass).- complement s. a group of more than 20 serum proteins, some of which can be serially activated and participate in a cascade resulting in cell lysis; the complement s. also functions in chemotaxis, opsonization, and phagocytosis.- conducting s. of heart [TA] the s. of atypical modified muscle fibers comprising the sinoatrial node, atrioventricular node and bundle, the right and left bundles, and their terminal subendocardial branches (the Purkinje network). SYN: complexus stimulans cordis [TA], systema conducens cordis.- cytochrome P-450 s. a heterogeneous group of enzymes that catalyze various oxidative reactions in the human liver, intestine, kidney, lung, and central nervous s.; these enzymes are involved in the metabolism of many endogenous and exogenous substrates, including drugs, toxins, hormones, and natural plant products. Cytochrome P-450 enzymes are classified on the basis of chemical structure (amino acid sequencing). The designation of each enzyme is CYP followed by a numeral for the family to which it has been assigned, a letter for its subfamily, and sometimes a second numeral for the individual enzyme.The steady increase in the number and variety of pharmaceutical agents available for the treatment of infections, degenerative and malignant conditions, mental disorders, and other diseases has led to polypharmacy, with attendant risks of undesirable drug interactions. Disturbances in the function of the cytochrome P-450 s. are increasingly recognized as important causes of such interactions. When a drug increases the formation of a P-450 enzyme, other drugs metabolized by that enzyme are eliminated more rapidly and may fail to produce the desired therapeutic effects. In contrast, a drug that inhibits P-450 enzyme activity can retard the metabolism of substrate drugs, with resultant increases in serum and tissue levels and in drug effects, including side effect s. Inhibition usually involves competition between drugs for the same binding site on an enzyme molecule. Reversible inhibition is the most common mechanism of drug interactions involving the P-450 s.. In general, drugs compete for a specific P-450 isoenzyme. Examples of agents that cause interactions through reversible inhibition are fluoroquinolone antibiotics, cimetidine, ketoconazole, and protease inhibitors used in the treatment of AIDS. CYP3A, the most abundant of human cytochrome P-450 enzymes, accounts for 30% of those found in the liver. Its substrates include many psychoactive medicines, ketoconazole, erythromycin, and protease inhibitors. This enzyme is inhibited by some antidepressants, azole antifungals, cimetidine, erythromycin, and other drugs. Increased formation of CYP3A is induced by carbamazepine, phenobarbital, phenytoin, and rifampin. Ethnic differences in the expression of CYP2D6 explain why whites are more likely than blacks and Asians to experience toxicity from accumulation and excessive serum levels of drugs metabolized by this enzyme, such as tricyclic antidepressants, SSRIs, antipsychotics, and beta-blockers.- ecological s. SYN: ecosystem.- endomembrane s. SYN: endoplasmic reticulum.- esthesiodic s. a s. of neurons and fiber tracts in the spinal cord and brain subserving sensation.- exterofective s. name applied by Cannon to the somatic nervous s. as opposed to the interofective or autonomic s..- extrapyramidal motor s. literally: all of the brain structures affecting bodily (somatic) movement, excluding the motor neurons, the motor cortex, and the pyramidal (corticobulbar and corticospinal) tract. Despite its very wide literal connotation, the term is more often used to denote in particular the striate body (basal ganglia), its associated structures (substantia nigra, subthalamic nucleus), and its descending connections with the midbrain.- feedback s. 1. a complex of neuronal circuits whereby a part of the efferent path returns to the input to modulate its activity, thus acting as a governor on the s.; 2. See feedback.- genital s. [TA] the complex s. consisting of the male or female gonads, associated ducts, and external genitalia dedicated to the function of reproducing the species. SYN: systema genitalia [TA], reproductive s..- geographic information s. a computer-based s. that combines cartographic capabilities with electronic data processing to rapidly produce customized maps for use in epidemiologic studies.- haversian s. SYN: osteon.- health information s. combination of vital and health statistical data from multiple sources, used to derive information about the health needs, health resources, use of health services, and outcomes of use by the people in a defined region or jurisdiction.- hematopoietic s. the blood-making organs; in the embryo at different ages these are the yolk sac, liver, thymus, spleen, lymph node s, and bone marrow; after birth they are principally the bone marrow, spleen, thymus, and lymph node s.- hepatic portal s. a venous portal s. 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.- heterogeneous s. in chemistry, a s. that contains various distinct and mechanically separable parts or phases; e.g., a suspension or an emulsion.- hexaxial reference s. the figure resulting if the lines of derivation of the unipolar limb leads of the electrocardiogram are added to the triaxial reference s..- His-Tawara s. the complex s. of interlacing Purkinje fibers within the ventricular myocardium. SEE ALSO: conducting s. of heart.- homogeneous s. in chemistry, a s. 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.- hypoxia warning s. a device designed to produce an audio or visual signal at a predetermined level of oxygen partial pressure; ideally, the s. would warn of impending hypoxia in time for corrective action to be taken.- immune s. an intricate complex of interrelated cellular, molecular, and genetic components which provides a defense (immune response) against foreign organisms or substances and aberrant native cells.- indicator s. in in vitro immunological tests, a combination of reagents used to determine the degree to which immunologic reagents have combined ( e.g., sensitized erythrocytes in complement-fixation tests; enzyme and substrate in enzyme-linked immunosorbent assays).- information s. combination of vital and health statistical data from multiple sources, used to derive information and make decisions about the health needs, health resources, costs, use, and outcome of health care.- International S. of Units International S. of Units.- interofective s. term applied by W. Cannon to the autonomic nervous s. as opposed to the somatic nervous s. or exterofective s..- kallikrein s. a blood serum s., the activity of which is initiated by factor XII (Hageman factor) leading to the production of prekallikrein activator and then to kallikrein which, after activation by plasmin, splits bradykinin from kininogen.- kinetic s. 1. a term proposed by G.W. Crile to denote the chain of organs through which latent energy is transformed into motion and heat : it includes the brain, the thyroid, the adrenals, the liver, the pancreas, and the muscles; 2. that part of the neuromuscular s. whereby active movements are effected; distinguished from the static s..- limbic s. collective term denoting a heterogeneous array of brain structures at or near the edge (limbus) of the medial wall of the cerebral hemisphere, in particular the hippocampus, amygdala, and fornicate gyrus; the term is often used so as to include also the interconnections of these structures, as well as their connections with the septal area, the hypothalamus, and a medial zone of mesencephalic tegmentum. By way of the latter connections, the limbic s. exerts an important influence upon the endocrine and autonomic motor systems; its functions also appear to affect motivational and mood states. SYN: visceral brain.- linnaean s. of nomenclature the s. of nomenclature in which the names of species are composed of two parts, a generic name and a specific epithet (species name, in botany). SYN: binary nomenclature, binomial nomenclature. [Carl von Linné]- lymphoid s. [TA] it consists of lymphatic vessels, nodes, and lymphoid tissue; it empties into the veins at the level of the superior aperture of the thorax. SYN: systema lymphoideum [TA], absorbent s., lymphatic s., systema lymphaticum.- masticatory s. the organs and structures primarily functioning in mastication : the jaws, teeth with their supporting structures, temporomandibular joint, muscles of mastication, tongue, lips, cheeks, and oral mucosa. SYN: dental apparatus, masticatory apparatus (1).- metameric nervous s. that part of the nervous s. which innervates body structures developed in ontogeny from the segmentally arranged somites or, in the head region, branchial arches. The term implies reference to the neural mechanisms intrinsic to the spinal cord and brainstem (represented by the sensory nuclei, motoneuronal cell groups, and their associated interneurons in the reticular formation); by strict definition it should exclude the autonomic nervous s..- meter-kilogram-second s. an absolute s. based on the meter, kilogram, and second; the basis of the International S. of Units.- metric s. a s. of weights and measures, universal for scientific use, based upon the meter, which was originally intended to be one ten-millionth of a quadrant of the earth's meridian and now is based on the length that light travels in a vacuum in a given period of time (see meter). Prefixes of the meter (and other standards) reflect either fractions or multiples of the meter and are identical to the International S. of Units (q.v.). The unit of weight is the gram, which is the weight of one cubic centimeter of water, equivalent to 15.432358 grains. The unit of volume is the liter or one cubic decimeter, equal to 1.056688 U.S. liquid quarts; a cubic centimeter is about 16.23073 U.S. minims.- mononuclear phagocyte s. (MPS) a widely distributed collection of both free and fixed macrophages derived from bone marrow precursor cells by way of monocytes; their substantial phagocytic activity is mediated by immunoglobulin and the serum complement s.. In both connective and lymphoid tissue, they may occur as free and fixed macrophages; in the sinusoids of the liver, as Kupffer cells; in the lung, as alveolar macrophages; and in the nervous s., as microglia. SYN: s. of macrophages.- nervous s. [TA] the entire nerve apparatus, composed of a central part, the brain and spinal cord, and a peripheral part, the cranial and spinal nerves, autonomic ganglia, and plexuses. SYN: systema nervosum [TA].- nonspecific s. SYN: reticular activating s..- occlusal s. the form or design and arrangement of the occlusal and incisal units of a dentition or the teeth on a denture. SYN: occlusal scheme.- oculomotor s. that part of the central nervous s. having to do with eye movements; it is composed of pathways connecting various regions of the cerebrum, brainstem, and ocular nuclei, utilizing multisynaptic articulations.- open s. a s. in which there is a continual exchange of material, energy, and information with the environment.- O-R s. abbreviation for oxidation-reduction s..- oxidation-reduction s. (O-R s.) an enzyme s. in the tissues by which oxidation and reduction proceed simultaneously through the transference of hydrogen or of one or more electrons from one metabolite to another. SEE ALSO: oxidation-reduction. SYN: redox s..- parasympathetic nervous s. parasympathetic part of autonomic division of peripheral nervous s., autonomic division of nervous s..- periodic s. the arrangement of the chemical elements in a definite order as indicated by their respective atomic numbers in such a way that groups of elements with similar chemical properties (similar valence shell electron number) are grouped together. See Mendeléeff law.- peripheral nervous s. [TA] the peripheral part of the nervous s. external to the brain and spinal cord from their roots to their peripheral terminations. This includes the ganglia, both sensory and autonomic, and any plexuses through which the nerve fibers run. SEE ALSO: autonomic division of nervous s.. SYN: pars peripherica systematis nervosi [TA], systema nervosum periphericum, peripheral part of nervous s..- portal s. a s. of vessels in which blood, after passing through one capillary bed, is conveyed through a second capillary network, as in the hepatic portal s. in which blood from the intestines passes through the liver sinusoids.- pressoreceptor s. the pressoreceptive areas which with their afferent fibers and connections with the autonomic s. react to a rise in arterial blood pressure and serve to buffer it by inhibiting the heart rate and vascular tone. SEE ALSO: baroreceptor.- projection s. the s. of axons carrying stimuli from one portion of the nervous s. to other portions.- properdin s. an immunologic s. 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 s. includes Factors B, D, H, and I. The s. 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.- renal portal s. an arterial portal s., in which efferent glomerular arterioles receive blood from the capillaries of the renal glomeruli and carry it to the peritubular capillary plexus surrounding the proximal and distal convoluted tubules. SYN: hypothalamohypophysial portal s. (2).- renin-angiotensin s. a selective regulator of the aldosterone biosynthetic pathway that acts by increasing aldosterone production and sodium retention as a result of volume depletion, with resulting increased renin production in the kidney and conversion of angiotensin I in the plasma to angiotensin II.- renin-angiotensin-aldosterone s. the hormones, renin, angiotensin, and aldosterone work together to regulate blood pressure. A sustained fall in blood pressure causes the kidney to release renin. This is converted to angiotensin in the circulation. Angiotensin then raises blood pressure directly by arteriolar constriction and stimulates the adrenal gland to produce aldosterone which promotes sodium and water retention by the kidney, such that blood volume and blood pressure increase.- respiratory s. [TA] all the air passages from the nose to the pulmonary alveoli. SYN: systema respiratorium [TA], apparatus respiratorius, respiratory apparatus.- reticular activating s. (RAS) a physiologic term denoting that part of the brainstem reticular formation that plays a central role in the organism's bodily and behavorial alertness; it extends as a diffusely organized neural apparatus through the central region of the brainstem into the subthalamus and the intralaminar nuclei of the thalamus; by its ascending connections it affects the function of the cerebral cortex in the sense of behavioral responsiveness; its descending (reticulospinal) connections transmit its activating influence upon bodily posture and reflex mechanisms ( e.g., muscle tonus), in part by way of the gamma motor neurons. SEE ALSO: reticular formation. SYN: nonspecific s..- reticuloendothelial s. (RES) a collection of putative macrophages, first described by Aschoff, which included most of the true macrophages (now classified under the mononuclear phagocytic s.) as well as cells lining the sinusoids of the spleen, lymph node s, and bone marrow, and the fibroblastic reticular cells of hematopoietic tissues; all of these latter cells are only weakly phagocytic and are not true macrophages. The term persists in the literature and is often equated with the mononuclear phagocytic s..- second signaling s. pavlovian term for speech in which words are considered to be the “second signals” capable of producing conditioned responses.- somesthetic s. sensory data derived from skin, muscles, and body organs in contrast to that derived from the five special senses.- static s. that part of the neuromuscular s. whereby the animal organism is maintained in posture and equilibrium and counteracts the forces of gravity and atmospheric pressure; distinguished from the kinetic s. (2).- stomatognathic s. all of the structures involved in speech and in the reception, mastication, and deglutition of food. SEE ALSO: masticatory s.. SYN: masticatory apparatus (2).- subendocardial conducting s. of heart terminal ramifications in the ventricles of the specialized conducting s. of the heart. SYN: Purkinje s..- T s. the transverse tubules that are continuous with the sarcolemma in skeletal and cardiac muscle fibers.- thoracolumbar s. See autonomic division of nervous s., sympathetic part of autonomic division of peripheral nervous s..- triaxial reference s. the figure resulting from rearranging the lines of derivation of the three standard limb leads of the electrocardiogram (as represented in the Einthoven triangle) so that, instead of forming the sides of an equilateral triangle, they bisect one another. SYN: Dieuaide diagram.- urinary s. [TA] all organs concerned with the formation, storage, and voidance of urine including kidneys, ureters, bladder, and urethra. SYN: systema urinarium [TA], urinary apparatus, uropoietic s..- urogenital s. includes all the organs concerned in reproduction and in the formation and voidance of urine. SYN: apparatus urogenitalis, genitourinary apparatus, genitourinary s., systema urogenitale, urogenital apparatus.- vertebral-basilar s. the arterial complex comprising the two vertebral arteries joining to form the basilar artery, and their immediate branches.- vertebral venous s. any of four interconnected venous networks surrounding the vertebral column; anterior external vertebral venous plexus [TA] (plexus vertebralis externus anterior [TA]), the small s. around the vertebral bodies; posterior external vertebral venous plexus [TA] (plexus vertebralis internus anterior [TA]), the extensive s. around the vertebral processes; anterior internal vertebral venous plexus [TA] (plexus vertebralis internus posterior [TA]), the s. running the length of the vertebral canal anterior to the dura; posterior internal vertebral venous plexus, the s. running the length of the vertebral canal posterior to the dura; the latter two constitute the epidural venous plexus. SYN: Batson plexus, plexus venosus vertebralis, vertebral venous plexus.
* * *sys·tem 'sis-təm n1 a) a group of body organs or structures that together perform one or more vital functions see CIRCULATORY SYSTEM, digestive system, endocrine system, limbic system, NERVOUS SYSTEM, REPRODUCTIVE SYSTEM, RESPIRATORY SYSTEMb) the body considered as a functional unit2) a manner of classifying, symbolizing, or schematizing <a taxonomic \system>
* * *n.(in anatomy) a group of organs and tissues associated with a particular physiological function, such as the nervous system or respiratory system.
* * *sys·tem (sisґtəm) [Gr. systēma a complex or organized whole] a set or series of interconnected or interdependent parts or entities (objects, organs, or organisms) that function together in a common purpose or produce results impossible to achieve by one of them acting or operating alone.
Medical dictionary. 2011.