Schematic representation of the renin angiotensin system. Additional components of the renin angiotensin system (RAS) pathway have been identified in recent years, increasing its complexity. The 'classical' components of the system are highlighted in bold and by underlined text (modified from  and incorporating parts of the discussion from ). Angiotensin metabolites are prefixed by Ang, with the number of amino acids present relative to the 14 amino acid angiotensinogen sequence order. Black arrows between peptide fragments denote enzymatic conversion steps catalyzed by a host of enzymes denoted in coloured circles or boxes according to the abbreviations listed below. Blue arrows from peptides to blue boxes denote receptor binding routes according to the main text. Note that the AngII metabolite AngIII is currently considered to be the main and a more potent mediator of many recognised AngII functions , and the binding of AngIV to its receptor is believed to affect cognitive function . Also note the ACE2-Ang(1–7)-Mas (receptor) axis, which is now currently believed to be a RAS internal regulatory mechanism to attenuate AngII-mediated functions (large red arrow centrally located in pathway; ACE2 is a recently discovered ACE homologue) . Abbreviations: ACE, angiotensin-1 converting enzyme; AP, aminopeptidase; DAP, dipeptidyl aminopeptidase; PCP, carboxypeptidase; PO, propyl oligopeptidase; REN, renin.