The circulatory system has one main job and that is to deliver oxygen to all the cells in the body. The heart pumps oxygen poor blood to the lungs to refill and pumps oxygen rich blood through the body to the cells. The oxygen connects to the hemloglobin in the red blood cells. which travels throught the artery to a smaller artery and to a smaller artery ect. ect.
Until it enters a capillary, the smallest of all vain's in the body. there walls are small enough for the oxygen in the cell to slip through to the out side cell.
Here you can see the vain's artery's and capilaries
Until it enters a capillary, the smallest of all vain's in the body. there walls are small enough for the oxygen in the cell to slip through to the out side cell.