What are the three distinct types of blood vessels? Describe each in few sentences.

Arteries

• Carry blood away from the heart and deliver oxygen-rich blood to the tissues of the body (except for the pulmonary artery which carries deoxygenated blood to lungs)
• Have very elastic wall which help to withstand the pressure created as the heart pumps the blood
• Each artery is lined by smooth tissue and has three layers:

outer tunica externa, comparatively thicker middle layer tunica media and inner tunica interna/endothelium.

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Veins

• Carries deoxygenated blood towards the heart (except pulmonary veins which carries oxygenated blood from lungs)
• Have thinner nonelastic wall
• Unlike to arteries they are under low pressure and rely on muscle contractions to return blood to the heart
• Have valves which prevent the blood from flowing in the opposite direction
• Also have three layers:

Capillaries

• Smallest of the body's blood vessels
• Have very thin wall made of only endothelium
• Perform oxygen, carbondioxide, nutrients and waste exchange between blood and tissues easily
• They are connection between veins and arteries

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