The circulatory system's main function is to transport materials. The organ that pumps blood is the heart. The heart is made up of four areas: the left atrium, the right atrium, the left ventricle, and the right ventricle. The blood in from either the superior vena cava or the inferior vena cava depending on which side of the body it came from. Then it enters the right atrium. From the right atrium it goes to the right ventricle. From there it goes to the pulmonary vein which leads to the capillaries in the lungs. The blood cells get oxygen by means of diffusion. After they leave the capillaries, they come to pulmonary vein, which is the only big vein that carries oxygen rich blood. From the vein the blood enters the left atrium. The blood goes from the left atrium to the left ventricle and then enters the aorta. From the aorta the blood goes into the medium arteries into the small arteries. From the small arteries into capillaries. From the capillaries into the small veins then the medium veins and back into the vena cava's.
blood is made up of plasma, red blood cells, platelets, and white blood cells. Plasma is a yellowish fluid that is mostly water and a little bit of fat and protein. Red blood cells (erythrocytes) carry hemoglobin. Hemoglobin is a protein that contains iron and helps transport some of the materials to and from the bloodstream. White blood cells (leukocytes) are cells that protect the body from invaders like bacteria and viruses. The white cells also digest the red blood cells when they mature and lose their nuclei. The white blood cells are almost twice as big as the red blood cells and the ratio of white blood cells to red blood cells is 1:500. Platelets are the blood particles that forms blood clots when you get a scrape or anything else that draws blood.
The components of the circulatory system are: