pertaining to circulation.
the major system concerned with the movement of blood
, consisting of the heart
, blood vessels
, and lymphatic vessels
. (See also color plates.) The circulatory system transports to the tissues and organs of the body the oxygen, nutritive substances, immune substances, hormones, and chemicals necessary for normal function and activities of the organs; it also carries away waste products and carbon dioxide. It equalizes body temperature and helps maintain normal water and electrolyte balance.
An adult has an average of 5 liters of blood in the body; the circulatory system carries this entire quantity on one complete circuit through the body every minute. In the course of 24 hours, over 6500 liters of blood pass through the heart.
The rate of blood flow through the vessels depends upon several factors: force of the heartbeat, rate of the heartbeat, venous return, and control of the arterioles and capillaries by chemical, neural, and thermal stimuli.
Pulmonary and Systemic Circulation
. There are in reality two independent circulatory systems within the body, each with its own pump inside the sheathing of the heart. In one of these systems, called the pulmonary circulation, the right side of the heart pumps blood through the lungs. In the lungs, the blood gives up its carbon dioxide and absorbs a fresh supply of oxygen. The reoxygenated blood then flows to the left side of the heart, and is pumped out again to all the systems and organs of the body. This major circulatory system is called the systemic circulation.
The circulation of blood through the fetus bypasses the pulmonary circuit (see also fetal circulation
. Blood pumped from the left side of the heart enters the aorta, the main arterial trunk of the systemic circulation. The aorta, which is about 1 inch in diameter, arches upward and toward the left side of the body. Just above the heart two coronary arteries branch off from the aorta. These arteries supply the muscles of the heart with blood.
Branching from the top of the aortic arch are three large arteries which supply the upper part of the body, the brachiocephalic trunk (which divides into the right carotid and right subclavian arteries) and the left carotid and left subclavian arteries. The carotid arteries supply the head and neck; the subclavian arteries supply the arms. The aorta then turns downward and passes through the trunk of the body, close to the vertebral column. Smaller arteries branch off from the aorta to supply the lungs, stomach, spleen, pancreas, kidneys, intestines, and other organs of the body. At about the level of the umbilicus, the aorta divides into two branches, the two iliac arteries, which supply the vessels of the pelvic organs and the legs.
The arteries so far named are the main conducting arteries. They consist of a smooth inner lining covered largely by elastic fibers that absorb the pulsations of the heart. As the heart beats, the elastic arterial walls damp the strong pulsations into a more nearly constant blood pressure.
Distributing arteries branch out from the conducting arteries. These arteries are composed largely of muscle fibers that encircle the smooth inner lining of the blood vessels and have the ability to contract and relax. The distributing arteries in turn branch out into arterioles, or little arteries, which are barely visible to the eye. The elastic walls of the arterioles and distributing arteries are under the control of the autonomic nervous system
. The arterioles lead directly to the capillaries.
Blood passes through the aorta at the speed of about 40 cm per second when the body is at rest, and at a faster rate when it is active. As the blood spreads through the distributing arteries and arterioles, its speed gradually diminishes. By the time the blood has reached the capillaries, it has slowed to a speed about one-eightieth of that in the arteries.
Capillaries. The complex network of innumerable and microscopically small capillaries distributed throughout the tissues supplies blood to all cells in the body. Each capillary is about 10 microns in diameter, about the size of a single blood cell; thus the blood cells must make their way through the capillaries in single file.
Despite their minute size, the capillaries have a vast total area. The capillary “lake” can be called the climax of the circulatory system, for it is here that the vital work of the circulatory system is carried out. Nutrients leaving the blood capillaries enter the capillary lake, a collection of tissue fluid which bathes each cell. From there the nutrients permeate the walls of the cells. Waste products of cell metabolism enter the capillary lake and eventually pass through the capillary wall and into the blood circulation. The capillary walls are selective; i.e., they permit the exchange of special nutrients and chemicals and bar the passage of unwanted substances. For example, the cells making up the walls of the capillaries in the brain bar the passage of many substances that might injure the brain cells, and the capillaries in the placenta also act as a barrier against substances that might be harmful to the developing fetus.
Venous System. From the capillaries the blood returns to the heart via the veins, which together make up the venous system. The blood flows from the capillaries to minute venules, and then to the veins, in a network of blood vessels of ever-increasing size that parallels in reverse the branching of the arterial system. The walls of the veins, however, are thinner, less elastic, and less muscular than those of the arteries. And whereas the arteries are for the most part buried deep within the body for protection, the venous system has many superficial veins that run close to the surface of the skin. If an arterial blood vessel is cut, the blood flows from the cut in spurts, whereas blood from a cut vein flows steadily.
The blood returning to the heart collects into two main veins. Blood returning from the arms, head and upper chest flows into the superior vena cava; blood returning from the rest of the body flows into the inferior vena cava. Both these veins return the blood to the right side of the heart.
The blood from the lower part of the body must return to the heart against the force of gravity, since all the pressure built up by the heart has been dissipated in the capillaries. This is accomplished in several ways. The veins themselves contain one-way venous valves which work in pairs. When the blood is flowing in the correct direction, the venous valves are pressed against the walls of the veins, permitting unobstructed flow. If the blood should tend to flow backward, however, the venous valves fall inward and press against each other, effectively stopping the backward flow of blood. The blood is “milked” upward toward the heart principally by the massaging action of the abdominal and leg muscles as they press against the veins. Inspirations of air also force the blood through the venous system, as do the movements of the intestines. If the leg muscles do not move for long periods of time, the blood collects in the lower part of the body and the amount available for the brain is decreased.
Systemic Circuits. The circulatory system has been discussed so far as if the blood flowed through the body in a simple circular path. In fact, the blood can take one of several circuits through the body. Among these circuits are the coronary circuit through the arteries and veins of the heart; a circuit through the neck, head, and brain; a circuit through the digestive organs; and the renal circuit through the kidneys. The importance of the renal circulation lies in the fact that the kidneys act as the cleansing filter of the circulatory system, removing a variety of products that have been cast off from the cells and body tissues. At any given time, about one-quarter of all the blood pumped through the body is passing through the renal circuit.
The most complex circuit (portal circulation) is that which flows through the digestive system, picking up proteins, carbohydrates, fats, and chemicals from the intestines and delivering them to the tissues. Separate distributing arteries conduct the blood to the lower intestine, upper intestine, stomach, spleen, and pancreas. The veins leading from these organs combine to form the portal vein, which leads to the liver. Within the liver, the artery leading to the liver (the hepatic artery) and the portal vein subdivide themselves into a complex network of capillary-like vessels called sinusoids which bring the blood into closer contact with the cells of the liver. The liver cells withdraw glucose from the blood for storage as glycogen or release it as needed, and remove from the blood many harmful substances that might be toxic to body tissues. The blood leaving the liver flows to the inferior vena cava.
. The cells, chemicals, and other components of the blood are suspended within the blood vessels in plasma. Similar fluid also fills the spaces between the tissue cells. Nutrients reaching the cells are carried there by this tissue fluid, and it also carries waste products from the cells to the capillaries. One function of the lymphatic system is to collect and return this fluid via the lymphatic vessels to the circulatory system. When this tissue fluid is within the lymphatic system, it is called lymph. In addition to draining off excess tissue fluid, the lymphatic capillaries also transport some waste products as well as dead blood cells, pathogenic organisms in case of infection, and malignant cells from cancerous growths. From the lymphatic capillaries the lymph is carried into larger lymphatic vessels which contain one-way valves similar to those in the veins. Lymph nodes are interspersed among the lymph vessels and filter their fluids. Eventually large lymph ducts (the thoracic duct and right lymphatic duct) empty into the right and left subclavian veins. The lymph is propelled by the same massaging action that causes the blood to circulate through the venous system. There are larger masses of lymphatic tissue called lymphatic organs, and among them are the spleen
, and thymus
. These organs produce specialized leukocytes (lymphocytes) that help protect the body against infections (see also immunity
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.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.