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The circulatory system (or cardiovascular system) is an organ system that moves nutrients, gases, and wastes to and from cells, and helps stabilize body temperature and pH to maintain homeostasis. While humans, as well as other vertebrates have a closed circulatory system, some invertebrate groups have open circulatory system. The most primitive animal phyla lack circulatory systems.
Human circulatory system
Furthermore, these components can either belong to the systemic circulation and the pulmonary circulation. The systemic circulation is the main part of the circulatory system, while the pulmonary system oxygenates the blood.
In the systemic circulation, arteries bring oxygenated blood to the tissues. As blood circulates through the body, oxygen diffuses from the blood into cells surrounding the capillaries, and carbon dioxide diffuses into the blood from the capillary cells. Veins bring deoxygenated blood back to the heart.
The release of oxygen from red blood cells or erythrocytes is regulated in mammals. It increases with an increase of carbon dioxide in tissues, an increase in temperature, or a decrease in pH. Such characteristics are exhibited by tissues undergoing high metabolism, as they require increased levels of oxygen.
De-oxygenated blood enters the right atrium of the heart and flows into the right ventricle where it is pumped through the pulmonary arteries to the lungs. Pulmonary veins return the now oxygen-rich blood to the heart, where it enters the left atrium before flowing into the left ventricle. From the left ventricle the oxygen-rich blood is pumped out via the aorta, and on to the rest of the body.
In the heart there is one atrium and one ventricle for each circulation, and with both a systemic and a pulmonary circulation there are four chambers in total: left atrium, left ventricle, right atrium and right ventricle.
Closed circulatory system
The circulatory systems of humans is closed, meaning that the blood never leaves the system of blood vessels. In contrast, oxygen and nutrients diffuse across the blood vessel layers and enters interstitial fluid, which carries oxygen and nutrients to the target cells, and carbon dioxide and wastes in the opposite direction.
The circulatory systems of all vertebrates, as well as of annelids (for example, earthworms) and cephalopods (squid and octopus) are closed, just as in humans. Still, the systems of fish, amphibians, reptiles, and birds show various stages of the evolution of the circulatory system.
In fish, the system has only one circuit, with the blood being pumped through the capillaries of the gills and on to the capillaries of the body tissues. This is known as single circulation. The heart of fish is therefore only a single pump (consisting of two chambers). In amphibians and most reptiles, a double circulatory system is used, but the heart is not always completely separated into two pumps. Amphibians have a three-chambered heart.
Birds and mammals show complete separation of the heart into two pumps, for a total of four heart chambers; it is thought that the four-chambered heart of birds evolved independently from that of mammals.
Open circulatory system
The open circulatory system is an arrangement of internal transport present in animals such as molluscs and arthropods, in which fluid (called hemolymph) in a cavity called the hemocoel bathes the organs directly and there is no distinction between blood and interstitial fluid; this combined fluid is called hemolymph or haemolymph. Muscular movements by the animal during locomotion can facilitate hemolymph movement, but diverting flow from one area to another is limited. When the heart relaxes, blood is drawn back toward the heart through open-ended pores.
Hemolymph fills all of the interior hemocoel of the body and surrounds all cells. Hemolymph is composed of water, inorganic salts (mostly Na+, Cl-, K+, Mg2+, and Ca2+), and organic compounds (mostly carbohydrates, proteins, and lipids). The primary oxygen transporter molecule is hemocyanin.
No circulatory system
Circulatory systems are absent in some animals, including flatworms (phylum Platyhelminthes). Their body cavity has no lining or enclosed fluid. Instead a muscular pharynx leads to an extensively branched digestive system that facilitates direct diffusion of nutrients to all cells. The flatworm's dorso-ventrally flattened body shape also restricts the distance of any cell from the digestive system or the exterior of the organism. Oxygen can diffuse from the surrounding water into the cells, and carbon dioxide can diffuse out. Consequently every cell is able to obtain nutrients, water and oxygen without the need of a transport system.
Health and disease
History of discovery
The valves of the heart were discovered by a physician of the Hippocratean school around the 4th century BC. However their function was not properly understood then. Because blood pools in the veins after death, arteries look empty. Ancient anatomists assumed they were filled with air and that they were for transport of air.
Herophilus distinguished veins from arteries but thought that the pulse was a property of arteries themselves. Erasistratus observed that arteries that were cut during life bleed. He ascribed the fact to the phenomenon that air escaping from an artery is replaced with blood that entered by very small vessels between veins and arteries. Thus he apparently postulated capillaries but with reversed flow of blood.
The 2nd century AD Greek physician, Galen knew that blood vessels carried blood and identified venous (dark red) and arterial (brighter and thinner) blood, each with distinct and separate functions. Growth and energy were derived from venous blood created in the liver from chyle, while arterial blood gave vitality by containing pneuma (air) and originated in the heart. Blood flowed from both creating organs to all parts of the body where it was consumed and there was no return of blood to the heart or liver. The heart did not pump blood around, the heart's motion sucked blood in during diastole and the blood moved by the pulsation of the arteries themselves.
Galen believed that the arterial blood was created by venous blood passing from the left ventricle to the right by passing through 'pores' in the interventricular septum, air passed from the lungs via the pulmonary artery to the left side of the heart. As the arterial blood was created 'sooty' vapors were created and passed to the lungs also via the pulmonary artery to be exhaled.
"...the blood from the right chamber of the heart must arrive at the left chamber but there is no direct pathway between them. The thick septum of the heart is not perforated and does not have visible pores as some people thought or invisible pores as Galen thought. The blood from the right chamber must flow through the vena arteriosa (pulmonary artery) to the lungs, spread through its substances, be mingled there with air, pass through the arteria venosa (pulmonary vein) to reach the left chamber of the heart and there form the vital spirit..."
Finally William Harvey, a pupil of Hieronymus Fabricius (who had earlier described the valves of the veins without recognizing their function), performed a sequence of experiments and announced in 1628 the discovery of the human circulatory system as his own and published an influential book about it. This work with its essentially correct exposition slowly convinced the medical world. Harvey was not able to identify the capillary system connecting arteries and veins; these were later described by Marcello Malpighi.
- Lymphatic system
- Noise health effects
- Blood vessels
- Innate heat
- Cardiac muscle
- Major systems of the human body
- Amato Lusitano
- William Harvey
- Iskandar, Albert Z. "Comprehensive Book on the Art of Medicine by Ibn al-Nafis". Retrieved May 2, 2005.
- Nie Jing-bao, " Refutation of the Claim that the Ancient Chinese described the Circulation of Blood," New Zealand Journal of Asian Studies 3, 2 (December, 2001): 119-135
- The Circulatory System, a comprehensive overview
- The InVision Guide to a Healthy Heart An interactive website
- NCP Cardiovascular Medicine A Journal Covering Clinical Cardiovascular Medicine
Human organ systems
|Cardiovascular system • Digestive system • Endocrine system • Immune system • Integumentary system • Lymphatic system • Muscular system • Nervous system • Reproductive system • Respiratory system • Skeletal system • Urinary system|
|Systemic circulation||Heart → Aorta → Arteries → Arterioles → Capillaries → Venules → Veins → Vena cava → Heart|
|Pulmonary circulation||Heart → Pulmonary arteries → Lungs → Pulmonary vein → Heart|
Prenatal development/Mammalian development of circulatory system
|Vascular||Blood island Cardinal veins - Ducts of Cuvier - Vitelline veins - Ductus venosus - Umbilical vein|
|Heart development||Primitive heart tube: Truncus arteriosus - Bulbus cordis - Primitive ventricle - Primitive atrium - Sinus venosus|
Septum primum (Ostium primum, Ostium secundum) - Septum secundum (Foramen ovale) - other septa (Endocardial cushions/Septum intermedium, Aorticopulmonary septum) - Atrial canal
Circulatory system pathology (I, 390-459)
|Hypertension||Hypertensive heart disease - Hypertensive nephropathy - Secondary hypertension (Renovascular hypertension)|
|Ischaemic heart disease||Angina pectoris (Prinzmetal's angina) - Myocardial infarction (heart attack) - Dressler's syndrome|
|Pulmonary circulation||Pulmonary embolism - Cor pulmonale|
|Pericardium||Pericarditis - Pericardial effusion - Cardiac tamponade|
|Endocardium/heart valves||Endocarditis - mitral valve (regurgitation, prolapse, stenosis) - aortic valve (stenosis, insufficiency) - pulmonary valve (stenosis, insufficiency) - tricuspid valve (stenosis, insufficiency)|
|Myocardium||Myocarditis - Cardiomyopathy (Dilated cardiomyopathy, Hypertrophic cardiomyopathy, Loeffler endocarditis, Restrictive cardiomyopathy) - Arrhythmogenic right ventricular dysplasia|
|Electrical conduction system|
of the heart
|Heart block: AV block (First degree, Second degree, Third degree) - Bundle branch block (Left, Right) - Bifascicular block - Trifascicular block|
Pre-excitation syndrome (Wolff-Parkinson-White, Lown-Ganong-Levine) - Long QT syndrome - Adams-Stokes syndrome - Cardiac arrest - Sudden cardiac death
Arrhythmia: Paroxysmal tachycardia (Supraventricular, AV nodal reentrant, Ventricular) - Atrial flutter - Atrial fibrillation (Familial) - Ventricular fibrillation - Premature contraction (Atrial, Ventricular) - Ectopic pacemaker - Sick sinus syndrome
|Other heart conditions||Heart failure - Cardiovascular disease - Cardiomegaly - Ventricular hypertrophy (Left, Right)|
|Cerebrovascular diseases||Stroke - Transient ischemic attack - Intracranial hemorrhage/cerebral hemorrhage: Extra-axial hemorrhage (Epidural hemorrhage, Subdural hemorrhage, Subarachnoid hemorrhage)|
Intra-axial hematoma (Intraventricular hemorrhages, Intraparenchymal hemorrhage) - Anterior spinal artery syndrome - Binswanger's disease - Moyamoya disease
|Atherosclerosis (Renal artery stenosis) - Aortic dissection/Aortic aneurysm (Abdominal aortic aneurysm) - Aneurysm - Raynaud's phenomenon/Raynaud's disease - Buerger's disease - Vasculitis/Arteritis (Aortitis) - Intermittent claudication - Arteriovenous fistula - Hereditary hemorrhagic telangiectasia - Spider angioma - Dissection (Carotid artery, Vertebral artery)|
|Veins, lymphatic vessels|
and lymph nodes
|Thrombosis/Phlebitis/Thrombophlebitis (Deep vein thrombosis, May-Thurner syndrome, Portal vein thrombosis, Venous thrombosis, Budd-Chiari syndrome, Renal vein thrombosis, Paget-Schroetter disease) - Varicose veins / Portacaval anastomosis (Hemorrhoid, Esophageal varices, Varicocele, Gastric varices, Caput medusae) - Superior vena cava syndrome - Lymph (Lymphadenitis, Lymphedema, Lymphangitis)|
|Other||Hypotension (Orthostatic hypotension) - Rheumatic fever|
|See also congenital (Q20-Q28, 745-747)|
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