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Homeostasi1 - calcium etc Often this homeostatic control...

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Homeostasis The difference between homeostasis as a single cell performs it and what a multicelled creature does derives from their basic organizational plan: a single cell can dump wastes outside the cell and just be done with it. Cells in a multicelled creature, such as a human or cat, also dump wastes outside those cells, but like the trash can or dumpster outside my house/apartment, those wastes must be carted away. The carting away of these wastes is accomplished in my body by the circulatory system in conjunction with the excretory system. For my house, I have the City of Phoenix sanitation department do that (and get to pay each month for their service!). The ultimate control of homeostasis is accomplished by the nervous system (for rapid responses such as reflexes to avoid picking up a hot pot off the stove) and the endocrine system (for longer-term responses, such as maintaining the body levels of
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Unformatted text preview: calcium, etc.). Often this homeostatic control takes the form of negative feedback loops. There are two types of biological feedback: positive and negative. Negative feedback turns off the stimulus that caused it in the first place. Your house’s heater (or cooler for those of us in the Sun Belt) acts on the principle of negative feedback. When your house cools off below the temperature set by your thermostat, the heater is turned on to warm air until the temperature is at or above what the thermostat is set at. The thermostat detects this rise in temperature and sends a signal to shut off the heater, allowing the house to cool of until the heater is turned on yet again and the cycle (or loop) continues. Positive feedback causes an amplification of the stimulus by the reaction. Examples of each will be presented below....
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