Blood vessel

• The human circulatory system is described as a closed circulatory system
• As blood journeys through the entire body, it remains confined within the network of blood vessels
• There are three kinds of blood vessels: artery, vein, and capillary
• Arteries are thick-walled to cope with the high pressure of the body flowing through it
• Arteries move blood away from the heart
• Most arteries in the body transport oxygenated (oxygen-rich) blood
• Starting from the aorta, the artery branches into smaller arteries until it becomes the smallest arteries, called arterioles
• Arteries have three layers:

  • Tunica Externa: Fibrous connective tissue forms the outer layer, which is very strong to prevent rupture or bursting of large arteries
  • Tunica Medica: Made of smooth muscle and elastic connective tissue, involved in maintaining normal blood pressure
  • Tunica Intima: The innermost layer in contact with blood, the same tissue type as the lining of the heart chambers
• Veins have thinner walls compared to arteries, making them easily collapse when cut
• Functionally, veins convey blood from all parts of the body to the heart
• Starting from the capillaries, the smallest veins, called venules, become larger and larger until they become the largest vein, called the vena cava
• Veins have valves that prevent backflow of blood, most numerous in veins of the legs
• Capillaries are the smallest blood vessels, one-cell thick
• Capillaries carry blood from arterioles to venules
• Exchange of materials such as gases and nutrients can easily take place between the blood and the cells