Blood circulation

The circulatory apparatus or cardiovascular system is based on a true network as wide as precise. Under the impulse of the Heart, vital leader, the blood-vessels, the Artery S and the Vein S, ensure the transport of the Sang (and consequently of oxygen, the nutrients, the hormones…) essential at all our organization. He also plays a part in the Thermorégulation.

History

The relation between the Bleeding and the Mort was undoubtedly highlighted very early in the history of humanity. The Égyptiens had identified the Sang like source of Vie and sits of the heart.

The dissections practiced by the Greek doctors of Cos at fifth century BC, in the line of Hippocrates, on cut the throat of animals induce errors of representation: the arteries are found empty, one thus thinks that they transport Air, while the Foie and the Rate are gorged with blood, these two bodies are thus regarded as important components of the transport of blood. Hérophile, doctor of Alexandria of fourth century BC, described the first palpation of the Pouls. It is with Erasistrate de Keos (320 - 250 av. J. - C.) that one owes the first description of the venous valves.

Galien (131 - 201) made a precise description of the network of veins and arteries starting from dissection of pigs, but interprets the role of the bodies wrongfully. According to him, blood is created in the liver starting from food, it circulates by the veins and goes on the one hand towards the lungs to mix with air, on the other hand passes from the ventricle right to the left ventricle by the porous wall where it takes heat which it redistributes in the body; arrived at the ends of the body, blood is consumed and arises in the form of Transpiration.

The Moslem Médecin S translate the Egyptian treaties of medicine discovered at the time of the invasion of Egypt at the 7th century, of which the treaty of Galien on circulation (translated by Averroès). As from the 10th century, they describe many cardiovascular diseases (Thrombose and Collapsus for Avicenne, Péricardite for Avenzoar). Ibn Al-Nafis describes the first pulmonary circulation (small circulation) and enrichment of blood in air by the lungs in 1242.

With the 16th century, Michel Servet (Spanish) described pulmonary circulation; it is supposed that he knew work of Ibn Nafis via their translation of André Alpago. Italian Realdo Colombo is the first to describe pulmonary circulation perfectly.

It is Andrea Cesalpino (1519 - 1603) which uses the first the term of “circulation” and which allots the role of it to the Cœur, whereas it was thought up to now that it was the liver which created the movement. It is William Harvey (1578 - 1657), raises Fabrice d' Acquapendente (1537 - 1619), which makes the first complete description of the circulatory system, in its work Exercitatio Anatomica de Motu Cordis and Sanguinis in animalibus of 1628. It describes in particular the direction of circulation and the exact role of the venous valvules, and establishes that circulation is important (several liters per minute) whereas one believed it in the drip. Marcello Malpighi identifies for the first time the capillaries with the microscope in 1661.

The work of Ibn Nafis remains been unaware of until in 1924 where Al Taoui, an Egyptian doctor, finds the translation of André Alpago in the national Bookstore of Berlin.

Veins and arteries

The heart must maintain a flow blood continuous within the circulatory apparatus. This last must ensure all fabrics of the organization a continuous contribution of Oxygène and nutrients, but also take care of the elimination of the Carbon dioxide and all waste. This system is composed of veins and arteries, each one filling of the different roles. The systemic circulation is distinguished (great circulation), whose role is the contribution of oxygen to fabrics and the pulmonary circulation (small circulation) whose role is to ensure the reoxygenation of blood by the lungs and elimination by those of carbonic gas.

By definition, an artery is a vessel containing the active blood of the heart to fabrics whereas a vein is a vessel containing the active blood of fabrics towards the heart. Consequently, in systemic circulation, the arteries bring blood oxygenated to fabrics and the veins bring back impoverished blood oxygenates some towards the heart. In pulmonary circulation, the blood impoverished of oxygen is brought to the lungs by the pulmonary arteries, it is oxygenated there, then it turns over in the middle by the pulmonary veins. In pulmonary circulation, the arteries thus transport blood low in oxygen and the pulmonary veins, oxygenated blood.

The venous return

The deep and surface veins are equipped with valvules. These “valves” preventing the backward flow, laid out all the four to five centimetres, impose an one way of circulation blood.

The aspiration of the blood of the feet towards the heart is the result of several mechanisms. Thus, the compression of the arch of the foot, the contraction of the muscles of the calves and the thighs drive out blood upwards. The respiratory movements also facilitate work by decreasing the pressure within the thorax at the time of each inspiration. This is why walk and the physical exercise make it possible to limit the risks of venous insufficiency.

Anatomy of the circulatory system

Media

Modeling of general and lymphatic blood circulation (animation flash).
Visualization of its content and blood circulation of O₂ and CO₂ (animation flash).

See too

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