The circulatory system can be likened to a tree.
The aorta is comparable to the main tree trunk. It branches into smaller arteries (like the thick branches
that come off the main trunk), which in turn divide into even smaller vessels (like smaller branches and
twigs) called arterioles, which carry blood to the capillaries (like the leaves). Capillaries are the microscopic
vessels that supply blood, with its load of oxygen and other nutrients, to each cell in the body.
After the oxygen is used up, the blood returns to the heart via a branching system of veins.