A living system, either as a whole or as a subsystem, such as human circulatory system, is always under the integrated nervous and humoral control of the whole body, i.e., in homeostasis. Multiple feedback mechanisms with mutual interactions among systems, organs, and even tissues provide integrated control of the entire body. These control mechanisms have different spatial coverages, from the micro- to macroscale, and different time constants, from nanoseconds to decades. This paper presents our approach using multi-scale computational analysis to understand macroscale as well as macroscale blood flows in human circulatory system.