The closed circulatory system is one in which the blood does not mix with other fluids or tissue. This type of circulatory system has all 4 components present, but they are separated by physical boundaries. For example, the vessels that transport blood through your body form a closed circuit when it comes back to start at the heart again. Unlike an open circulation where only part of this cycle can be seen and mixed together, in a closed circulation there are no gaps for any substances to escape from. In order for water (or another substance) to leave the bloodstream and enter tissues such as muscle cells, oxygen must first diffuse out so that space will be made available inside these cells for more fluid consumption.