It circulates to the heart through the atria from the veins and the ventricles send oxygen rich blood through the arteries to all parts of the body. The difference between arteries and veins is not the oxygen content, but rather the direction of the blood flow. Veins carry blood toward the heart and arteries carry it away.

In the human circulatory system, we have a double circulation because there is a separate pulmonary circuit to the lungs and a systemic circuit to the body. These arteries and veins lie close to each other and are involved it countercurrent heat / cool exchanges. the major veins in the arm are the cephalic vein, the basilic vein, and the median cubital vein which run alongside the brachial artery, the ulnar artery, and the radial artery which circulate from the shoulders to the tips of your fingers.

The brachial artery in the upper arm above the elbow is where the blood pressure reading is taken through an instrument called the sphygmometer. The pressure cuff is placed on the upper arm over the brachial artery (near the humerus arm bone) which changes to the ulnar artery and the radial artery below the elbow. To take the pulse at the wrist it is taken through the beats per minute counted on the radial artery (near the radius bone ) which is on the thumb side of the forearm. The ulnar artery rest near the ulna (a bone on the inside part of the forearm with the palm rotated facing up on the side of the baby finger).