A blood reservoir is an organ or vessel that holds large proportions of blood, and veins are vessels termed as the blood reservoirs of the body. This is because they hold the largest amount of blood, which is about 50 to 60 percent of the entire body’s blood volume.
The veins are also called capacitance vessels due to their blood holding characteristic. They have thin walls and much wider lumens compared to the arteries, thereby enabling them to contain much more blood than any other human vessel. Veins exist all throughout the body, making them ideal blood reservoirs.
These blood reservoirs have a very low pressure and are only able to move blood back and forth through expansion and contraction of their walls aided with the help of valves. Veins are most abundant in venous sinuses. The major veins are the coronary sinus, located in the heart, and the dural sinuses that move blood to and from the brain.
The spleen is an organ in the body that can also act as a reservoir for blood in case of massive blood loss or hemorrhagic shock. It also filters the blood and recycles iron on destruction of the red blood cells.