Srotas is the unique concept in Ayurveda. As is the case with vata which is the inevitable component in every movement, so is the case with srotas which provides the pathway for every movement. These channels need not be anatomically present always; sometimes it is a physiological channel, sometimes it is a biochemical channel and so on. It shows that visualizing the srotas as a vessel or tube is an injustice done to the observational skills of our great Ayurvedic vaidyas and gurus. They have definitely recognized the unparalleled physiological and biochemical events occurring in our bodies and summarized all those events into the concept of srotas.
Following this principle, a blood vessel should never be considered as rasavaha or raktavaha srotas only. Instead by understanding the physiological events occuring inside the circulatory system we can suggest that it is combination of many srotas working at the same time. All those functions of each of the srotas are going on inside the circulatory system. This is how the concepts in Ayurveda should be understood.