Circulatory system Guide, Meaning , Facts, Information and Description
The circulatory system or cardiovascular system is the organ system which circulates blood around the body of most animals.
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2 Circulatory systems of different species 3 History of discovery 4 See also 5 External links |
The circulatory systems of all vertebrates as well as of earthworms, 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.
All circulatory systems frequently employ countercurrent exchange systems to drive the diffusion of chemicals into or out of the bloodstream.
The now oxygenated blood returns to the left atrium in the pulmonary veins.
The deoxygenated blood from the capillaries of the gastrointestinal tract drains into the portal vein which, instead of going directly back to the heart, leads to the liver. This allows the liver to take up the nutrients that were extracted by the intestines from food. The liver also neutralizes some toxins taken up by the intestines. Blood from the liver drains via the hepatic veins into the inferior vena cava and then the right side of the heart.
There is also a small portal flow from the hypothalamus to the anterior pituitary gland.
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 pulse is 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 1268 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.
This is an Article on Circulatory system. Page Contains Information, Facts Details or Explanation Guide About Circulatory system Functions
Following are some basic functions of the human circulatory system:
Circulatory systems of different species
Non-human animals
The circulatory system of arthropods 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 hemolymph is drawn back into the heart as the heart relaxes.No Circulatory system
An example of an animal with no circulator system is the flatworm (class Tubellaria). 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.Humans
The human circulatory system is comprised of the blood, the vascular system, and the heart.Pulmonary circulation
The right ventricle pumps deoxygenated blood into the pulmonary arteries. These arteries carry the blood to the lungs, where it passes through a capillary network close to air-filled alveoli. This enables the release of carbon dioxide and the uptake of oxygen from the air.Portal circulation
There are two exceptions to the system of double circulation. Lymphatic system
In the capillaries, some of the plasma seeps into the tissues to become interstitial fluid. This fluid is returned to the bloodstream as lymph, via the lymphatic system, a system of lymph vessels separate from the circulatory system and without a central pump.Fetal circulation
The circulatory system of the fetus is different, as the fetus does not use its lungs yet and obtains oxygen and nutrients from the placenta through the umbilical cord. After birth, the fetal circulatory system undergoes several anatomical changes, including closure of the ductus arteriosus and foramen ovale.History of discovery
See also
External links