Although the heart plays one of the most important roles in the circulatory system, the rest of the system is also very important because it is the one that transports blood to and from the heart to keep the body alive. . Blood is carried throughout the body by blood vessels. Blood vessels are complex structures but can be greatly simplified. The two main components of blood vessels are arteries and veins. Arteries carry oxygenated blood away from the heart, while veins carry deoxygenated blood back to the heart. Other blood vessels present in the circulatory system are arterioles and Venules. Arterioles are blood vessels that branch from arteries and lead to capillaries. Venules resemble arterioles but branch off into veins and also lead to capillaries. Finally, capillaries are the smallest blood vessels that connect arterioles and Venules and play an important role in the exchange of gases like oxygen. Say no to plagiarism. Get a tailor-made essay on “Why Violent Video Games Should Not Be Banned”? Get the original essayThe endothelium can be found throughout the circulatory system. This is the thin, permeable layer of cells found on the inner walls of all blood vessels. Permeability is the ability of a membrane to allow the transport of certain molecules through it. Endothelium permeability is important because oxygen, nutrients, and white blood cells must be transported through blood vessels to reach other organs. The three main functions of blood include transport, protection and regulation. Blood carries many different nutrients throughout the body, blood plays a key role in protection as it decreases inflammation, carries antibodies which destroy bacteria and carries platelets which trigger clotting and finally, blood is useful in regulation of the body. For example, the blood, along with the nervous system, is responsible for regulating pH and water balance. Although blood vessels are responsible for many different tasks in the human body, they are not involved in regulating blood transport. Blood transport is controlled by the nervous system. The nervous system is responsible for telling blood vessels when to contract and when to dilate. When the body is hot, vasodilation occurs, which is when the diameter of blood vessels increases, allowing more blood to reach the surface of the skin to cool the body. When the body is cold, vasoconstriction occurs, which is when the diameter of blood vessels decreases, keeping heat in the body. Blood pressure is the amount of force exerted on the walls of blood vessels by circulating blood. Blood pressure decreases as blood vessels move from arteries to arterioles to capillaries to veins. However, blood pressure generally refers to the pressure in the arteries because they are used the most. Blood pressure can be measured in two phases; systolic and diastolic pressure. Systolic pressure is the pressure measured at the highest point, at the beginning of the cardiac cycle, while diastolic pressure is the pressure measured at the lowest point, the resting phase of the heart. Although the circulatory system is considered one large system, there are many subsystems within it. The pulmonary circuit is the part of the circulatory system that carries blood to and from the heart. The pulmonary circuit is made up of the pulmonary vein which..