HUMAN CIRCULATORY SYSTEM

Our body also needs a transportation system to deliver nutrients, oxygen, and carbon dioxide. The transportation system in our body is the circulatory system, which consists of the heart, blood vessels, and blood.

A.        Blood Vessels

In the cardiovascular system, there are three types of blood vessels:

1.       Artery

(Picture. Human blood  circulation system)

Artery is a blood vessel transporting blood from heart throughout the body. They are hidden inside our body. The biggest artery is the one closest to the heart called aorta. Aorta branches into artery. Artery still brances into smaller artery called arteriole. At the tip of arteriole, it is formed many soft branches and it becomes capillary beds called artery capillaries.

2.       Vein

Vein is blood vessel transporting blood from the body back to heart. They are located near our skin surface and look bluish. The walls of veins are thin and not elastic. You cannot feel their pulse. Veins have valves along their length. Their function is to keep the blood flowing in one direction. Besides that, they also maintain blood flows since there is no pump in these veins.

The differences of artery and vein

No	Characteristics	Artery	Vein
1	Stream direction	Away from the heart	Toward the heart
2	Vessel’s wall	Thick and elastic	Thin and not elastic
3	Beat	Can be felt	Cannot be felt
4	Locaton	Far from skin surface	Near skin surface
5	Valve	One near the heart	Along the vessels
6	Blood characteristic	Clean, except pulmonary artery ( carry blood to the lungs)	Dirty, except pulmonary vein ( carry blood from lungs back to the heart)

3.       Capillaries

The blood vessels branch into smaller vessels called capillaries.

At the tip of the capillaries, arteries and veins join. Therefore, our blood vessel is a closed blood vessel. Our blood always flows or remains in blood vessels.

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A.        Heart

Heart is necessary to pump the blood throughout the body and located slightly on left side in chest cavity. The heart size is almost the same as our fists. Heart muscle is similar with skeletal muscle, but it has branch structure (anastomose). Human heart is devided into four chambers:

a)      left atrium, have function to pumping blood into  the left ventricle

b)      right atrium, have function to pumping blood into  the right ventricle

c)       left ventricle, have function to pumping throughout the body through aorta              

d) right ventricle, have function to pumping blood into lungs through pulmonary artery.        
      The ventricle will has a thicker muscle wall than the atrium. It is because ventricles have to work harder, namely to pump blood to all parts of body. There are valves between the atrium and ventricle. The valves function as to prevent blood from flowing back to the atrium. Heart wall is composed of three layers, pericardium ( the outermost layer), myocardium ( central layers), and endocardium ( the innermost layer of heart chamber).

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