The cardiovascular system is a network of muscles and hallow tubes that transport blood and nutrients throughout the body. The cardiovascular system is actually two systems; one is the pulmonary system, which takes blood from the heart to the lungs and then back to the heart, and the other is the circulatory system, which sends the blood from the heart to the body and back. Without the cardiovascular system, the body could not function.
Heart
The heart is a hallow muscle the size of an adult fist that is composed of four chambers. The chambers help to keep oxygen-rich blood and oxygen-poor blood separated. The lower chambers are larger and called ventricles. The upper chambers are called atria. The atria are always taking blood into the heart, and the ventricles are always moving blood away from the heart. The left side of the heart deals with oxygen-rich blood, while the right side deals with oxygen-poor blood. When the heart does not beat, blood is not being circulated. The Mayo Clinic states that the heart beats, on average, 35 million times a year.
Arteries
Arteries are hallow tubes with thin, muscular walls in between smooth, elastic tissue and a thicker, tougher covering. The muscle and elasticity allow the arteries to withstand the pressure of the pulsing blood. Arteries are responsible for carrying blood away from the heart. Generally, the arteries contain oxygen-rich blood. The only artery that does not carry oxygenated blood is the pulmonary artery. The largest artery in the body is the aorta, and it branches directly off the left ventricle of the heart. As the arteries move further away from the center of the body, they get smaller and smaller. At a certain point, the arteries become arterioles, and then they become capillaries.
Capillaries
Capillaries are a very important part of the cardiovascular system. The capillaries have such a small diameter that only one blood cell can pass through at a time. According to KidsHealth.org, it is in these small areas of the circulatory system that oxygen is released and carbon dioxide is picked up from the surrounding tissues. The capillaries begin to get larger as they move closer to the center of the body and turn into venules.
Veins
Venules are smaller veins, and they gradually become larger, until they form into two large veins. Veins are thinner than arteries says KidsHealth.org, but they also have valves in them that shut if the blood tries to move backward. The system is made to keep blood flowing in one direction. All veins take blood to the heart and, generally, carry deoxygenated blood. The only vein that carries oxygenated blood is the pulmonary vein, which takes blood from the lungs to the heart.
Lungs
The lungs are made of an elastic, spongy tissue. The lungs have a very rich blood supply and membranes called alveoli, which are only one cell thick. These alveoli are responsible for helping the blood cells release carbon dioxide and obtain oxygen. Each breath in and out supplies the body with new oxygen cells.
