(3) Modes for the function of endogenous signals Endocrine Act on a far away organ via blood circulation, seen in most hormones Paracrine ct on a nearby target, seen in GFs, CKs, etc Synaptic: Presynaptic to postsynaptic(neurotransmitters Autocrine Act on itself after secreted, seen in GFs, especially in tumor tissues Intracrine Act on itself before secreted, seen in nuclear receptorsEndocrine Act on a far away organ via blood circulation, seen in most hormones Paracrine Act on a nearby target, seen in GFs, CKs, etc Synaptic: Presynaptic to postsynaptic (neurotransmitters) Autocrine Act on itself after secreted, seen in GFs, especially in tumor tissues Intracrine Act on itself before secreted, seen in nuclear receptors (3) Modes for the function of endogenous signals