An Introduction to Molecular Biotechnology. Группа авторовЧитать онлайн книгу.

       Endocrine signals (hormones) are produced by endocrinal gland cells (Table 3.2) and are released into the bloodstream. They circulate through the body and are picked up by receptors in the target cells – sometimes in a very distant part of the body – where they spring into action. In other words, hormones have a systemic effect. Hydrophilic and polar hormones (adrenaline and growth factors) bind to cell surface receptors, whereas lipophilic hormones (e.g. steroidal hormones, thyroxine, retinoic acid, vitamin D3) diffuse into the target cells to bind to intracellular receptors. These act as transcription regulators, controlling the expression of hormone‐regulated genes.Paracrine signals have an effect on their immediate surroundings. Released from a tissue cell, they are recognized and processed by neighboring cells. Their effect is local (e.g. prostaglandins).In direct cell‐to‐cell interaction, a cell presents a membrane‐bound signaling molecule to another cell carrying a membrane receptor that recognizes the molecule. Examples are found in the immune system (e.g. MHC complex and T‐cell receptors).In neuronal signal transduction, an electric signal (action potential) is transformed into a chemical signal at the synapse. Neurotransmitters are released that are recognized and processed by the receptors of a postsynaptic target cell.