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Human Body

46 46 47 47 HomEostAsIs patterns in status quo Imagine all the various communications going on at this very moment between all the people on this planet, then cram all that into the same size as you, and thats about how busy it is in there. This subconscious frenzy has one goal to maintain equilibrium. Consider circulating calcium levels, honed by parathyroid hormone PTH and calcitonin. High calcium stimulates calcitonin release, to which signal bone cells respond by crystallizing calcium, while kidney cells excrete it, reducing current levels. PTH has opposite effects, and raises calcium levels when they fall. Together these two negative feedback loops keep calcium at the desired level. Sets of similar loops balance everything from levels of ions to temperature, blood pressure, posture, vision, sanity, and so on, using chains of electrical and chemical signals. Signalling between cells creates integrated patterns of activity, by turning processes on and off inside cells using secondary intracellular signals. Gene switching, usually under hormonal control, tends to govern the longer term variations in cellular activities, whereas short term changes are mainly under electrical control by nerve impulses. Neuroendocrine integration of these regulatory feedback loops keeps the bodys patterns in status quo, which is homeostasis. Positive feedback loops are rare, as they amplify wildly. Apart from triggering ovulation, they occur in communication between humans, helping social equilibrium. They often involve the hormone oxytocin, which is busy during childbirth, breastfeeding, and orgasms. Oxytocin also mediates the spinetingling music reflex, and its limbic system effects say I love you.
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