Exosomes released in the bloodstream, illustration. Exosomes are released from one cell (blue, left) to activate others (red, background). The cellular packages called exosomes have membranes studded with various sets of proteins, fats and other particles. Ranging from 30 to 100 nanometres across, exosomes travel to distant cells in a variety of body fluids. Here, they are being released into the bloodstream.