THE CARDIOVASCULAR SYSTEM, WHICH IS MOSTLY DEVOTED TO TRANSPORTING OXYGEN AND NUTRIENTS, CAN ALSO PROVIDE  A HIGHLY EFFICIENT, BUT RELATIVELY SLOW SYSTEM FOR DELIVERING “SOLUBLE” MESSENGER MOLECULES TO ESSENTIALLY EVERY CELL IN THE BODY.
	HOWEVER TO ENSURE FIDELITY AND SPECIFICITY OF THE SIGNALLING PROCESS THESE “SOLUBLE MESSENGERS” MUST BE GUIDED TO THE CORRECT DESTINATION BY A “MOLECULAR ADDRESS”