Blood vessel

Human blood vessels have the function to drain blood from the heart to all parts of the body. Based on its function, there are three kinds of blood vessels contained in the human body: arteries, veins, and capillaries.


Arteries 
Arteries are blood vessels that carry blood out of the heart. Arteries that have the largest size is called the aorta. Aorta serves to carry blood from the left ventricle of the heart to the rest of the body.

Meanwhile, the vessels that carry blood from the right ventricle of the heart to the lungs are called pulmonary arteries.

The arteries emit a blood that contains much oxygen, except the pulmonary artery. Pulmonary arteries drain blood that contains a lot of carbon dioxide. The artery will branch off into smaller sizes and the edges are directly related to the body's cells. These branches are called capillary blood vessels.

Veins
Veins are vessels that carry blood from all parts of the body to the heart. The veins also branched out into venules. The vein forms smaller branches called capillaries. Veins that are directly related to the heart and lungs are called vena cava.

There are two kinds of vena cava namely inferior vena cava and superior vena cava. Inferior vena cava serves to drain blood from the lower body to the heart. Meanwhile, superior vena cava serves to drain the blood from the upper body to the heart.

Veins carry blood that contains a lot of carbon dioxide, except the pulmonary vein. The pulmonary veins drain the oxygen-rich blood, from the lungs to the heart.

Veins have a vessel wall that is thinner than the arteries, less elastic and the hole is larger than the artery. Veins have several valves that serve to prevent blood from reversing.

Capillary Vessels
Capillary vessels are very small blood vessels that are an extension of the arteries and veins. The cell walls of the capillary constituent comprise only a layer of cells and are permeable so that the body fluid or dissolved substances can go in and out through their cell walls.

In addition, in the capillary vessel also occurs the exchange of oxygen, carbon dioxide and nutrients and the results of excretion of tissue around the capillaries.

Capillary blood vessels can vary. Usually, the capillary blood vessels will narrow when humans are at low temperatures. Whereas, if the ambient temperature is high or the influence of chemicals such as histamine, the capillary blood vessels will expand.
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