1. pertaining to measures or measurement.
having the meter
as a basis.
the system of units of measurement that is based on the meter
, and liter
and in which new units are formed from the basic terms by prefixes denoting multiplication by a power of ten. See also si units
1. a set or series of interconnected or interdependent parts or entities (objects, organs, or organisms) that act together in a common purpose or produce results impossible by action of one alone.
an organized set of principles or ideas. adj., adj
The parts of a system can be referred to as its elements or components; the environment of the system is defined as all of the factors that affect the system and are affected by it. A living system is capable of taking in matter, energy, and information from its environment (input), processing them in some way, and returning matter, energy, and information to its environment as output.
system is one in which there is an exchange of matter, energy, and information with the environment; in a closed
system there is no such exchange. A living system cannot survive without this exchange, but in order to survive it must maintain pattern and organization in the midst of constant change. Control of self-regulation of an open system is achieved by dynamic interactions among its elements or components. The result of self-regulation is referred to as the steady state; that is, a state of equilibrium. homeostasis
is an assemblage of organic regulations that act to maintain steady states of a living organism.
A system can be divided hierarchically into subsystems, which can be further subdivided into sub-subsystems and components. A system and its environment could be considered as a unified whole for purposes of study, or a subsystem could be studied as a system. For example, the collection of glands in the endocrine system can be thought of as a system, each endocrine gland could be viewed as a system, or even specific cells of a single gland could be studied as a system. It is also possible to think of the human body as a living system and the endocrine system as a subsystem. The division of a system into a subsystem and its environment is dependent on the perspective chosen by the person studying a particular phenomenon.
Systems, subsystems, and suprasystems. Within the environment there are suprasystems, such as human society, and systems within the suprasystem, such as the educational and industrial systems and the health care delivery system. Within the health care delivery system are subsystems, such as the patient, family members, the nurse, the physician, and allied health care professionals and paraprofessionals.
in the behavioral system model
of nursing, the patterned, repetitive, and purposeful behaviors of an individual.
the heart and blood vessels, by which blood is pumped and circulated through the body; see also circulatory system
) a system for classifying cell-surface markers
expressed by lymphocytes based on a computer analysis of monoclonal antibodies
against hla antigens
, with antibodies having similar specificity characteristics being grouped together and assigned a number (CD1, CD2, CD3, etc.); these CD numbers are also applied to the specific antigens recognized by the various groups of monoclonal antibodies
. See also CD antigen
(CGS) (cgs) a system of measurements in which the units are based on the centimeter
as the unit of length
, the gram
as the unit of mass
, and the second
as the unit of time
the neurons in the central core of the brainstem
from the thalamus to the medulla oblongata, connecting the cerebral hemispheres
conduction system (conductive system (of heart)) the system of atypical cardiac muscle fibers, comprising the sinoatrial and atrioventricular nodes, internodal tracts, atrioventricular bundle, bundle branch, and terminal ramifications into the Purkinje network.
Emergency Medical Services (EMS) system a comprehensive program designed to provide services to the patient in the prehospital setting. The system is activated when a call is made to the EMS operator, who then dispatches an ambulance to the patient. The patient receives critical interventions and is stabilized at the scene. A communication system allows the health care workers at the scene to contact a trauma center for information regarding further treatment and disposition of the patient, followed by transportation of the patient to the most appropriate facility for treatment.
the system of ductless glands and other structures that produce internal secretions (hormones
) that are released directly into the circulatory system, influencing metabolism and other body processes; see endocrine glands
expert system a set of computer programs designed to serve as an aid in decision making.
gateway system a software interface between an online searcher and one or more search systems, facilitating the use of the system by searchers who are unfamiliar with it, or with online retrieval in general.
a haversian canal
and its concentrically arranged lamellae, constituting the basic unit of structure in compact bone (osteon
Haversian system: Structures of compact and spongy bone with the central haversian canal surrounded by the lamellae. From Applegate, 2000.
heterogeneous system a system or structure made up of mechanically separable parts, as an emulsion or suspension.
His-Purkinje system the intraventricular conduction system from the bundle of His to the distal Purkinje fibers, which carries the impulse to the ventricles.
Home Health Care Classification system see home health care classification system.
homogeneous system a system or structure made up of parts that cannot be mechanically separated, as a solution.
) (hypothalamo-hypophysial portal system
) the venules connecting the hypothalamus
with the sinusoidal capillaries of the anterior lobe of the pituitary gland
; they carry releasing substances to the pituitary.
lay health system a system comprising an informal referral network and sources of treatment outside the formal biomedical sources of health care; it includes individual consultation and information-seeking through significant others and peers concerning health behaviors, symptoms, and evaluation of treatment before, during, and after consultation with health care professionals.
in the omaha system
, anything connected with law or its administration; it includes legal aid, attorney, courts, or Child Protective Services (CPS), and many other agencies and officials.
limbic system a system of brain structures common to the brains of all mammals, comprising the phylogenetically old cortex (archipallium and paleopallium) and its primarily related nuclei. It is associated with olfaction, autonomic functions, and certain aspects of emotion and behavior.
lymphoid system the lymphoid tissue of the body, collectively; it consists of primary (or central) lymphoid tissues, the bone marrow, and thymus, and secondary (or peripheral) tissues, the lymph nodes, spleen, and gut-associated lymphoid tissue (tonsils, Peyer's patches).
mononuclear phagocyte system
the group of highly phagocytic cells that have a common origin from stem cells of the bone marrow and develop circulating monocytes and tissue macrophages, which develop from monocytes that have migrated to connective tissue of the liver (kupffer's cells
), lung, spleen, and lymph nodes. The term has been proposed to replace reticuloendothelial system
, which includes some cells of different origin and does not include all macrophages.
in the self-care model
of nursing, all the actions and interactions of nurses and patients in nursing practice situations; nursing systems fall into three categories: wholly compensatory, partly compensatory, and supportive-educative.
oxygen delivery system a device that delivers oxygen through the upper airways to the lungs at concentrations above that of ambient air. There are two general types: the fixed performance or high flow type, which can supply all of the needs of a patient for inspired gas at a given fractional inspired oxygen; and the variable performance or low flow type, which cannot supply all of the patient's needs for oxygen and delivers fractional inspired oxygen that varies with ventilatory demand.
peripheral nervous system
the portion of the nervous system
consisting of the nerves and ganglia outside the brain and spinal cord.
an arrangement by which blood collected from one set of capillaries passes through a large vessel or vessels and another set of capillaries before returning to the systemic circulation, as in the pituitary gland (the hypothalamo-hypophysial portal system
) or the liver (the hepatic portal circulation).
the group of specialized organs whose specific function is to provide for the transfer of oxygen from the air to the blood and of waste carbon dioxide from the blood to the air. The organs of the system include the nose
, the pharynx
, the larynx
, the trachea
, the bronchi
, and the lungs
. See also respiration
and Plates 7 and 8.
in the general systems framework and theory of goal attainment
, an organized boundary system of social roles, behaviors, and practices developed to maintain balance for growth, development, and performance, which involves an exchange of energy and information between the person and the environment for regulation and control of stressors.
in the omaha system
, the circle of friends, family, and associates that provide love, care, and need gratification; it may include church, school, workplace, or other groupings.
unit dose system a method of delivery of patient medications directly to the patient care unit. Following review by a nurse, a copy of the physician's original order is sent to the pharmacy, where the pharmacist reviews it again. The pharmacist then fills the order and delivers the medication to the patient care unit, usually in a 24-hour supply. Each patient has an individual supply of medications prepared and labeled by the pharmacist.
the system formed in the body by the kidneys
, urinary bladder
, and urethra
, the organs concerned in the production and excretion of urine
vasomotor system the part of the nervous system that controls the caliber of the blood vessels.
SI units; the metric system
Système International (SI) units
At an international convention in 1960, the General Conference of Weights and Measures agreed to an International System of Units: SI or Système International, the name for the current version of the metric system, first introduced in France at the end of the 18th century.
In any system of measurement, the magnitude of some physical quantities must be arbitrarily selected and declared to have unit value. These magnitudes form a set of standards and are called base units. All other units are derived units.
The SI measurement system is used for medical, scientific and technical purposes in most countries and comprises seven base units with several derived units. Each unit has its own symbol and is expressed as a decimal multiple or submultiple of the base unit by use of the appropriate prefix; for example, a millimetre is one thousandth of a metre.
SI base units
|Name of unit||Symbol||Quantity|
|Mole||mol||Amount of substance|
SI derived units (obtained by dividing or multiplying two or more base units)
|Joule||J||Work, energy, heat|
|Volt||V||Electrical potential, potential difference, electromotive force|
|Other values expressed in terms of base units|
|Metres per seond||m/s m.s-1||Speed, velocity|
|Metres per second per second||m/s2 m.s-2||Acceleration|
|Kilogram per cubic metre||kg/m3 kg.m-3||Density|
|Mole per cubic metre||mol/m3 mol.m-3||Concentration|
Decimal multiples and submultiples
The metric system uses multiples of 10 to express number. Multiples and submultiples of the base unit are expressed as decimals, with appropriate prefix to the name of the unit. The most widely used prefixes are kilo, milli and micro: e.g. 0.000 001 g = 10-6 g = 1 microgram.
Rules for using units and numbers
The symbol for a unit is unaltered in the plural and should not be followed by a full stop except at the end of a sentence: 5 cm not 5 cm. or 5 cms.
The decimal point between digits is indicated by a full stop. Commas are not used to divide large numbers into groups of three: a space is left after every third digit. If the numerical value of the number is less than 1, a zero should precede the decimal point: 0.123 456 not .123,456.
The SI symbol for 'day' (i.e. 24 hours) is 'd' but excretion of substances, fluid intake or output, for example, should preferably be expressed as amount or mass or volume 'per 24 hours'.
'Squared' and 'cubed' are expressed as numerical powers and not by abbreviation: square centimetre is cm2 not sq cm.
Multiples and submultiples of units
|1 000 000 000 000||1012||tera||T|
|1 000 000 000||109||giga||G|
|1 000 000||106||mega||M|
|0.000 000 001||10-9||nano||n|
|0.000 000 000 001||10-12||pico||p|
|0.000 000 000 000 001||10-15||femto||f|
|0.000 000 000 000 000 001||10-18||atto||a|
Units used for common measurements
Temperature The SI base unit is the kelvin but temperature is normally expressed in degrees Celsius (°C).
1° Celsius = 1° Centigrade
Energy The SI unit joule replaces the calorie.
1 calorie = 4.2 J
1 kilocalorie (calorie) = 4.2 kilojoules
Energy requirement, expenditure and content of food are expressed in kilojoules (kJ), but the kilocalorie (kcal) remains in common use.
Amount of substance in SI units is expressed in moles (mol), and concentration (amount per unit volume) in moles per litre (mol/L) or millimoles per litre (mmol/L). This replaces milliequivalents per litre (mEq/L). There are some exceptions: grams per litre (g/L), e.g. for haemoglobin and plasma proteins; international units (IU, U or iu) for enzyme activity.
Pressure The SI unit is the pascal (Pa); the kilopascal (kPa) replaces millimetres of mercury pressure (mmHg) for arterial blood pressure and partial pressure (or tension) of oxygen and carbon dioxide (PO2 and PCO2) in gas or in blood.
1 mmHg = 133.32 Pa
1 kPa = 7.5006 mmHg
Arterial blood pressure is, however, still widely measured in mmHg, cerebrospinal fluid pressure in mmH2O and central venous pressure in cmH2O.
Volume is calculated as length × width × depth. The metre(m) is the SI unit for length but a cubic metre is not a practical unit of volume for most purposes. The litre (L or l - the volume of a 10 cm cube) and the millilitre (mL, ml) are therefore used (1 L = 10-3 m3 = 1 dm3).
Weights and measures
|1 kilometre (km)||= 1000 metres (m)|
|1 metre (m)||= 100 centimetres (cm) or 1000 millmetres (mm)|
|1 centimetre (cm)||= 10 millimetres (mm)|
|1 millimetre (mm)||= 1000 micrometres (μm)|
|1 micrometre (mm)||= 1000 nanometres (nm)|
|1 metre (m)||= 39.370 inches (in)|
|1 centimetre (cm)||= 0.3937 inches (in)|
|30.48 centimetres (cm)||= 1 foot (ft)|
|2.54 centimetres (cm)||= 1 inch (in)|
|1 litre (L)||= 1000 millilitres (mL)|
|1 millilitre (mL)||= 1000 microlitres (mL)|
|1 litre (L)||= 1.76 pints (pt)|
|568.25 millilitres (mL)||= 1 pint (pt)|
|28.4 millilitres (mL)||= 1 fluid ounce (fl oz)|
|1 kilogram (kg)||= 1000 grams (g)|
|1 gram (g)||= 1000 milligrams (mg)|
|1 milligram (mg)||= 1000 micrograms (μg)|
|1 microgram (mg)||= 1000 nanograms (ng)|
|1 kilogram (kg)||= 2.204 pounds (lb)|
|1 gram (g)||= 0.0353 ounce (oz)|
|453.59 grams (g)||= 1 pound (lb)|
|28.34 grams (g)||= 1 ounce (oz)|
Conversions where x is the temperature to be converted.
For Body Temperature: Figure 2.
Figure 1: Conversion scales.
Figure 2: Conversion scale for body temperature showing the normal and abnormal ranges.