Circulatory system: Encyclopedia - Circulatory system

Circulatory system

The circulatory system or cardiovascular system is the organ system which circulates blood around the body of most animals.

Circulatory system - Types of circulatory systems

Circulatory system - Open circulatory system

The circulatory system of arthropods (for example, a grasshopper) and most mollusks is open, meaning that there are no capillaries and veins: one or more hearts pump the blood (more properly called hemolymph in this case) through the arteries to spaces called sinuses which surround the organs, allowing the tissues to exchange materials with the hemolymph. The blood soaks the organs and tissues and allows the exchange of gases, wastes and other nutrients. The blood travels freely throughout the organism but is being circulated by the hemolymphs. The hemolymph is drawn back into the heart as the heart relaxes.

Circulatory system - Closed circulatory system

The circulatory systems of all vertebrates, as well as of annelids (for example, earthworms) and cephalopods (squids and octopuses) are closed, meaning that the blood never leaves the system of blood vessels consisting of arteries, capillaries and veins.

The systems of fish, amphibians, reptiles, birds and mammals show various stages of evolution.

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 reptiles, a double circulation 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 of that of mammals.

Circulatory system - No circulatory system

An example of an animal with no circulatory system is the flatworm (class Turbellaria). Their body cavity has no lining or fluid. They have a mouth leading into a digestive system. The digestive system is very branched, and because the worm is so flat, digested materials can be diffused to all the cells of the flat worm. Oxygen can diffuse from water into the cells of the flatworm. Thus every cell is able to obtain nutrients, water and oxygen without the need of a transport system

Circulatory system - Human Circulation a closed circulatory system

Deoxygenated blood (blood containing no oxygen) from the veins of the body collect into two major veins-the superior vena cava and inferior vena cava. The superior and inferior vena cava empty into the right atrium. The right atrium is the larger of the two atriums because it needs to be able to hold the increased amount of blood. The blood is then pumped through the tricuspid atrioventicular valve into the right ventricle. From the right ventricle, blood is pumped through the pulmonary semi-lunar valve into the pulmonary trunk. The deoxygenated blood leaves the heart by the pulmonary arteries and travels through the lungs (where it is oxygenated) and into the pulmonary vein. The oxygenated blood then enters the left atrium. The blood then travels through the bicuspid valve, or mitral valve, into the left ventricle. The left ventricle is thicker and more muscular than the right ventricle becuase it pumps the blood throughout the body, systemic circulation. From the left ventricle, blood is pumped through the semi-lunar valve into the aorta. Once the blood goes through systemic circulation, deoxygenated blood will again be found inside the vena cava and the process will continue.

Circulatory system - Measurement techniques

• Electrocardiogram
• Sphygmomanometer
• Pulse meter

Circulatory system - Health and disease

• See heart disease

Circulatory system - 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.

Galen in the 2nd century AD knew that blood vessels carry 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.

Ibn Nafis in 1242 was the first person to accurately describe the process of blood circulation in the human body. Contemporary drawings of this process have survived. In 1552 Servetus described the same and Realdo Colombo proved the concept. All these results were not widely accepted however.

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
• Blood vessels

Adapted from the Wikipedia article "Circulatory system", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki