循环系统

本条目是关于动物循环系统。如果想了解植物世界请参看维管组织。

循环系统 (心血管系统)是一个向细胞和从细胞运送物质的器官系统。循環系統維持体温和体内pH值稳定（动态平衡）。环系统可分為三大類（从简到繁）：无循环系统、开循环系统及闭循环系统。

无循环系统

An example of an animal with no circulatory system is the flatworm (phylum Platyhelminthes). 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.

开放循环系统

An open circulatory system is an arrangement of internal transport present in some invertebrates like mollusks and arthropods in which circulatory fluid in a cavity called the hemocoel (also spelled haemocoel) bathes the organs directly and there is no distinction between blood and interstitial fluid; this combined fluid is called hemolymph (also spelled 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 细胞。

淋巴主要由水、无机盐（主要是Na⁺、Cl^-、K⁺、Mg²⁺和Ca²⁺)和有机化合物（主要是碳水化合物、蛋白质和脂類）组成。氧氣主要由血蓝蛋白運輸。

There are free-floating cells, the hemocytes, within the hemolymph. They play a role in 節肢動物的免疫系统.

闭循环系统

循环系统主要由心脏、血液和血管组成。

所有脊椎動物，以及环节动物（例如蚯蚓）和头足动物（如乌贼和章鱼）的循環系統都是閉循環系統，血液不會離開血管，包括动脉、毛细血管和静脉。

Arteries bring oxygenated blood to the tissues (except pulmonry arteries), and veins bring deoxygenated blood back to the heart (except pulmonary veins). Blood passes from arteries to veins through capillaries, which are the thinnest and most numerous of the blood vessles.

鱼、两栖动物、爬行动物、鸟和哺乳动物顯示演化的不同階段。

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 双循环系统 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.

哺乳动物循环

去氧血(containing little or no oxygen) collects in two major veins: the 上腔静脉 and the inferior vena cava. The superior and inferior vena cava empty into the 右心房. The coronary sinus which brings blood back from the heart itself also empties into the right atrium. The right atrium is the larger of the two atriums because it needs to be able to hold the larger amount of blood coming from the body (as opposed to the amount coming from the lungs). The blood is then pumped through the tricuspid atrioventicular valve into the 右心室. 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 肺静脉. The oxygenated blood then enters the 左心房. The blood then travels through the bicuspid valve, also called mitral valve, into the 左心室. The left ventricle is thicker and more muscular than the right ventricle because it pumps blood throughout the body, systemic circulation. From the left ventricle, blood is pumped through the semi-lunar valve into the 大动脉. Once the blood goes through systemic circulation, deoxygenated blood will again collect inside the vena cava and the process will continue.

测量技术

健康和疾病

发现历史

The valves of the heart were discovered by a physician of the Hippocratean school around the 公元前4世纪. 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.

公元2世纪希臘醫學家蓋倫 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.1552年, Michael Servetus described the same, and Realdo Colombo proved the concept. All these results were not widely accepted however.

Finally 法布里休斯 (who had earlier described the valves of the veins without recognizing their function) 的學生William Harvey　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.

参看

外部链接

Cardiovascular Topics
Studies on Hemodynamics and Coronary Circulation
The Circulatory System, a comprehensive overview
The InVision Guide to a Healthy Heart An interactive website

参考

Iskandar, Albert Z. "Comprehensive Book on the Art of Medicine by Ibn al-Nafis". Retrieved May 2 2005.

Cardiovascular system | Exercise physiology

生理學 | 循環系統

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