circulatory system

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pertaining to circulation.
circulatory system the major system concerned with the movement of blood and lymph, 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).
Arterial System. 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.
Lymphatic System. 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, tonsils, 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.
2. an organized set of principles or ideas. adj., adj systemat´ic, system´ic.

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.

An open 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.
alimentary system digestive system.
apothecaries' system see apothecaries' system.
autonomic nervous system see autonomic nervous system.
avoirdupois system see avoirdupois system.
behavioral system in the behavioral system model of nursing, the patterned, repetitive, and purposeful behaviors of an individual.
cardiovascular system the heart and blood vessels, by which blood is pumped and circulated through the body; see also circulatory system.
CD system (cluster designation) 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.
centimeter-gram-second system (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.
central nervous system see central nervous system.
centrencephalic system the neurons in the central core of the brainstem from the thalamus to the medulla oblongata, connecting the cerebral hemispheres.
circulatory system see circulatory system.
client system in the general systems framework and theory of goal attainment, the composite of physiological, psychological, sociocultural, and developmental variables that make up the total person.
colloid system (colloidal system) colloid (def. 3).
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.
digestive system see digestive system.
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.
endocrine system 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.
environmental control system environmental control unit.
expert system a set of computer programs designed to serve as an aid in decision making.
extrapyramidal system see extrapyramidal system.
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.
genitourinary system the organs concerned with production and excretion of urine, together with the reproductive organs. (See Plates.) Called also urogenital system.
haversian system 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.
health care system see health care system.
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.
hypophyseoportal system (hypophysioportal system) (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.
immune system see immune system.
interpersonal system in the general systems framework and theory of goal attainment, two or more individuals interacting in a given situation.
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.
legal system 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.
lymphatic system see lymphatic system.
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).
lymphoreticular system the lymphoid and reticuloendothelial systems considered together; see also lymphoreticular disorders.
metric system see metric system.
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.
nervous system see nervous system.
nursing system 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.
Omaha system see omaha system.
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.
parasympathetic nervous system see parasympathetic nervous system.
peripheral nervous system the portion of the nervous system consisting of the nerves and ganglia outside the brain and spinal cord.
personal system in the general systems framework and theory of goal attainment, the unified self, a complex whole that is rational, conscious, and feeling and that sets goals and decides on the means of achieving them.
pituitary portal system hypothalamo-hypophysial portal system.
portal system 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).
renin-angiotensin-aldosterone system see renin-angiotensin-aldosterone system.
respiratory system 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.
reticular activating system see reticular activating system.
reticuloendothelial system see reticuloendothelial system.
safety system see safety system.
SI system see SI units.
skeletal system see skeletal system.
social system 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.
support system 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.
sympathetic nervous system see sympathetic nervous system.
Unified Medical Language system see unified medical language system.
Unified Nursing Language system see unified nursing language system.
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.
urinary system the system formed in the body by the kidneys, ureters, urinary bladder, and urethra, the organs concerned in the production and excretion of urine.
urogenital system genitourinary system.
vascular system circulatory system.
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.

vas·cu·lar sys·tem

the cardiovascular and lymphatic systems collectively.
Synonym(s): circulatory system
Farlex Partner Medical Dictionary © Farlex 2012

circulatory system

1. The system of structures in vertebrates consisting of the heart, blood vessels, and lymphatics, by which blood and lymph are circulated throughout the body.
2. A similar system by which a fluid, such as hemolymph, is distributed in other animals.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.

circulatory system

The cardiovascular 'plumbing,' heart, arteries, capillaries, veins, which transport oxygenated blood from the lungs and heart to the general circulation, and return deoxygenated systemic blood to the lungs and heart. See Heart.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.

circulatory system

Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005

Patient discussion about circulatory system

Q. Why do people with a better cardiovascular fitness have lower heart rate? I recently met my old friend and that too after long time. We did go out and had a blast. He did show me his medical report and I was shocked to find out that he was having lower heart rate than me but was having better cardiovascular. He told me that it was quite normal but It was bothering me a lot. How could it be possible and I do see this as a deficiency. My friend does not agree with me and he told me that nothing to worry. I did try to research and found nothing with this regards. I am unable to sleep and would like to know on this. Can someone help me with answers?. Why do people with a better cardiovascular fitness have lower heart rate?

A. A strong athletic heart gets more cardiac output per stroke.
Less strokes = more movement of blood per stoke

More discussions about circulatory system
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References in periodicals archive ?
However, the exception are the indicators of the number of circulatory system diseases and fertility.
In Redcar & Cleveland during 2007 there were 490 deaths from diseases of the circulatory system (34.5% of all deaths).
Eliminating smoking is of utmost importance to preserve a healthy circulatory system. Although we do not have a huge amount of data on this topic, secondary smoke may also be a contributing factor to vascular problems.
Experiments conducted in the late 1940s and early 1950s suggested that many drowning deaths resulted from electrolyte disturbances or cardiac arrhythmia produced by high volumes of water entering the circulatory system through the lungs.
Benefit: Cocoa is rich in antioxidants, and the caffeine stimulates your circulatory system ...
MORE than a third of all deaths in Lozells and east Handsworth are caused by diseases of the circulatory system such as heart disease and stroke.
American Shared Hospital Services generates almost all of its profit from providing hospitals with the Gamma Knife, an instrument used to treat arteriovenous malfunctions (which involve the body's circulatory system) and certain brain tumors without making an incision.
Through this procedure, each pairs of mice developed shared circulatory system.
Though most valuable when purchased as a complete set, each book individually is valuable: members of this group include NERVOUS SYSTEM AND SENSE ORGANS (0313324565), URINARY SYSTEM (0313324026), REPRODUCTIVE SYSTEM (0313324492), RESPIRATORY SYSTEM (0313324244), SKELETAL SYSTEM (0313325219), MUSCULAR SYSTEM (0313324034), LYMPHATIC SYSTEM (0313324948), ENDOCRINE SYSTEM (0313326991), DIGESTIVE SYSTEM (0313326800), and CIRCULATORY SYSTEM (0313324018).
When we look at the dendritic pattern of a river and its tributaries and branches, it is like looking at the human circulatory system. We have all observed how water naturally forms vortices, as it flows in streams or even down the bathtub drain.
(1) Compared with nonpregnant women of the same age, pregnant and recently pregnant women aged 25-34 and 35-49 had reduced risks of death from cancer (relative risks, 0.3 for each), and those in the latter age-group had a reduced risk of death from diseases of the circulatory system (0.3).
It has not yet been determined whether lead affects blood pressure indirectly through changes in kidney function, or via more direct effects on the circulatory system or neurological blood pressure control.