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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 the most primitive animal phyla lack circulatory systems, some invertebrate groups have 'open circulatory system'. Vertebrates have a 'closed circulatory system'.

Contents

Open circulatory system

Closed circulatory system

Mammalian circulation

No circulatory system

Measurement techniques

Health and disease

History of discovery

See also

References

External links

Open circulatory system

An '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.
There are free-floating cells, the hemocytes, within the hemolymph. They play a role in the arthropod immune system.

Closed circulatory system

The main components of the circulatory system are the heart, the blood, and the blood vessels.
The circulatory systems of all vertebrates, as well as of annelids (for example, earthworms) and cephalopods (squid and octopus) are ''closed'', meaning that the blood never leaves the system of blood vessels consisting of arteries, arterioles, capillaries, veins and venules.
Arteries bring oxygenated blood to the tissues (except pulmonary arteries), and veins bring deoxygenated blood back to the heart (except pulmonary and portal veins). Blood passes from arteries to veins through capillaries, which are the thinnest and most numerous of the blood vessels and these capillaries help to join tissue with arterioles for transportation of nutrition to the cells.
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.

Mammalian circulation

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.
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. The relatively de-oxygenated blood collects in the venous system which coalesces into two major veins: the superior vena cava (roughly speaking from areas above the heart) and the inferior vena cava (roughly speaking from areas below the heart). These two great vessels empty into the right atrium of the heart. The coronary sinus empties the heart's veins themselves into the right atrium. The right atrium is the larger of the two atria, although both receive the same amount of blood. The blood is then pumped through the tricuspid valve, or right atrioventricular valve, into the right ventricle. From the right ventricle, blood is pumped through the pulmonary semi-lunar valve into the pulmonary artery. This blood enters the two pulmonary arteries (one for each lung) and travels through the lungs, where it is oxygenated and then flows into the pulmonary veins. This oxygenated blood then enters the left atrium, which pumps it through the bicuspid valve, also called the mitral or left atrioventricular valve, into the left ventricle.
From the left ventricle, blood is pumped through the aortic semi-lunar valve into the aorta, a massive and thick-walled artery. The aorta arches and gives off major arteries to the upper body before piercing the diaphragm in order to supply the lower parts of the body with its various branches. Once the blood enters the peripheral tissues oxygen and nutrients are extracted from it and carbon dioxide and wastes added, and it will again be collected in the veins and the process will be repeated. Peripheral tissues do not fully deoxygenate the blood, so venous blood does have oxygen, but in a lower concentration than in arterial blood.
The left ventricle is thicker and more muscular than the right ventricle because it pumps blood at a higher pressure. The left ventricle pumps blood to the entire body whereas the right ventricle pumps all of its blood directly to the lungs
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.

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.

Measurement techniques

★ Electrocardiogram

★ Sphygmomanometer

★ Pulse meter

★ Stethoscope

★ Pulse

Health and disease

Main articles: Cardiovascular disease

Main articles: Congenital heart defect

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.
In 1242 the Arab physician Ibn al-Nafis became the first person to accurately describe the process of blood circulation in the human body, including pulmonary circulation. He stated:

"...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..."

Contemporary drawings of this process have survived. In 1552, Michael Servetus described the same, and Realdo Colombo proved the concept, but it remained largely unknown in Europe.
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.

See also

★ Cardiology

★ Lymphatic system

★ Noise health effects

★ Blood vessels

★ Innate heat

★ Cardiac muscle

★ Major systems of the human body

★ Heart

References

★ 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

External links

★ 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