Four Types of Cell-Signalling

• Many signal molecules of the same type are used the different types of signalling; crucial differences lie in speed and selectivity of the signals are delivered to their target cell
• Action of Hormones (endocrine signalling): Hormone released from endocrine gland in body, transported in blood to target cells with specific complementary receptors; once they bind, it causes a sequence of events in the target cell
• Action of Cytokines (paracrine signalling): Cytokines are chemicals released by cells into tissue fluid and act locally on surrounding cells; in immune response, macrophages act as APCs to communicate with T and B lymphocytes
• Action of Neurotransmitters (neuronal signalling): Signals are transmitted from one neurone to another across synapses to remote target cells; using neurotransmitters
• Cell-Cell Contact: May also respond via direct contact to molecules on the surface of adjacent cells; cell surface molecules maybe proteins, glycoproteins or glycolipids