The Circulatory System
The Circulatory System
Circulatory System is the combined function of the heart, blood, and blood vessels to transport oxygen and nutrients to organs and tissues throughout the body and carry away waste products. The circulatory system increases the flow of blood to meet increased energy demands during exercise and regulates body temperature. Also, when foreign substances or organisms invade the body, the circulatory system quickly sends disease-fighting elements of the immune system, such as white blood cells and antibodies, to places under attack. In the case of injury or bleeding, the circulatory system sends clotting cells and proteins to the affected site, which quickly stop bleeding and promote healing.
The heart, blood, and blood vessels are the three main elements that make up the circulatory system. The heart is the engine of the circulatory system. It is divided into four chambers, the right atrium, the right ventricle, the left atrium, and the left ventricle. The walls of these chambers are made of a muscle called myocardium, which contracts to pump blood. The pumping action of the heart occurs in two stages for each heartbeat. Diastole, when the heart is at rest, and systole, when the heart contracts to pump deoxygenated blood toward the lungs and oxygenated blood to the body. There are typically about 60 to 90 beats per minute. If the heart stops pumping, death usually occurs within four to five minutes.
Blood consists of three types of cells, red blood cells that carry oxygen, disease-fighting white blood cells, and blood-clotting platelets, which are all carried through plasma. Plasma is yellowish and consists of water, salts, proteins, vitamins, minerals, hormones, dissolved gases, and fats.
Three types of blood vessels make a network of tubes throughout the body. Arteries carry blood away from the heart, and veins carry it toward the heart. Capillaries are tiny links between the arteries and the veins where oxygen and nutrients spread to body tissues. The inner layer of blood vessels is lined with cells that create a smooth passage for the transfer of blood. This inner layer is surrounded by connective tissue and smooth muscle that help the blood vessel to expand or contract. Blood vessels expand during exercise to meet the increased demand for blood and to cool the body. Blood vessels contract after an injury to reduce bleeding and also to conserve body heat.
Arteries have thicker walls than veins...