The 30 trillion or so cells in your body require a continuous supply of oxygen and nutrients and an unending removal of waste materials. the blood carries these materials in the body's circulation within a series of closed tubes, called

Sounds like Your cardiovascular system, the closed tubes must be your blood vessels, siencey  term: your Angio, which means blood vesels

When a virus infects a host cell, it uses the cell's machinery to make copies of its own genetic material in a process called replication. finally, during the process of self-assembly, that protein shell and the copies of the virus's genetic material are assembled into new viruses.