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Lecture 21 Signal Transduction

Lecture 21 Signal Transduction - BME 418 Quantitative Cell...

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BME 418, Quantitative Cell Biology Alan J. Hunt Lecture #21: Signal Transduction I: hormones and receptors Coordination of cellular activities is critical to multi-cellular life. This requires that cells communicate with one another and detect environmental properties. What sort of external signals can a cell detect? - Light, sound, mechanical, chemical, heat: definitely. - Electric currents: somewhat unusual, but clear importance in cells such as heart tissue that contain "gap junctions". Some aquatic animals such as sharks, electric eels, and torpedoes have mechanisms for detecting, and sometimes generating electric fields. More controversial is direct response to electric fields as a mechanism for communication between cells that do not have contiguous cytoplasm. For example, fish keratinocytes motility can be directed by an electric field, but it is unclear if this is physiologic since the fields are much higher than anything known to occur in the fish. - Electromagnetic Fields, Radio Waves: not likely in most cases since it has an extremely weak effect in biological tissues which are poor conductors at the size scales necessary to detect EMF. The only absolutely clear-cut evidence for a response to EMF is in some motile bacteria, but there is reasonable evidence for migratory birds and possibly salmon. In all of these cases the response is to static fields, not waves. Reports of harmful effect from everyday EMF are probably bogus (poorly controlled, weak statistics, conflicting, most importantly they lack any credible underlying hypothesis for how this could occur.) - High energy EMF (i.e. microwaves) has obvious effects on cells (it cooks them), but clearly this serves no physiologic purpose. We'll start with cell to cell signalling, which is most commonly mediated by chemicals called hormones: 1) endocrine : signal long distances, hormone typically released into blood.
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