Circulatory System Essay

The heart and blood are the transport system in the body. This assignment looks at the structure and function of the circulatory system and also includes a diagram of the circulatory system. The heart is a hollow muscular organ which acts as a pump, located in the chest and lies left behind the sternum.’ Blood vessels also transport blood throughout the body’ (Wikipedia). There are 3 major types of vessels which will be discussed later in the assignment. The blood is a main component of the body. It is used to transport materials, act as a defence against disease, helps regulates temperature of the body and helps with blood clotting. The blood is made up of 4 elements: Plasma, Red blood cells-erythrocytes, White blood cells-Leucocytes and Platelets. Plasma makes up the main composition of blood with 55% volume. It contains 90-92% water and is slightly thick and is straw coloured fluid. Red blood cells-erythrocytes are made in the bone marrow of the ribs and sternum and are broken down in the spleen and liver. The main function is to carry oxygen. White blood cells-Leucocytes are larger than red blood cells. Their main function is to protect the body from certain infections. Platelets are formed in the red bone marrow. It has an important function in blood clotting. Blood vessels are comprised of 3 main units, arteries, veins and capillaries. Arteries carry blood away from the heart. Their structure is made up of a thick, stretchy muscular wall, they have a narrow central tube and they contain no valves. Arteries branch into smaller tubes called arterioles and then into capillaries. Their main function is to carry oxygenated blood. Veins carry blood towards the heart. Its structure is made up of thin walls with little muscle, they have a wide central tube and they also contain valves. Veins branch into venules and then into capillaries. Veins main function is to carry deoxygenated blood. Capillaries carry blood between arteries and veins. Their structure is of a thin wall with only one cell thick and a very natural central tube. Substances can only leave or enter the bloodstream through the capillaries. ‘They are mainly responsible for bringing necessary substances to the cells and draining waste materials away’ (Encyclopedia Britanica). There are 4 chambers, or open spaces inside the heart that fill with blood. Two of these are called the atria; the other two are called the ventricles. ‘The left ventricle contracts most forcefully, so you can best feel your heart pumping on the left side of your chest’ (www.fi.edu). The pathway of blood through the human heart consists of a pulmonary circuit and a systemic circuit. Deoxygenated blood flows through the heart in one direction, entering through what is known as a superior vena cava and then into the right atrium which is then pumped through the tricuspid valve into the right ventricle before being pumped out through the pulmonary valve to the pulmonary arteries into the lungs. It then returns from the lungs via the pulmonary veins to the left atrium where it is pumped through the mitral valve into the left ventricle before leaving through the aortic valve to the aorta. In conclusion this assignment has looked at the functions and structure of the circulatory system. It has also identified the diagram of the circulatory system.