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Homeostasis and Feedback LoopsHomeostasisrelates to dynamic physiological processes that help us maintain an internal environmentsuitable for normal function. Homeostasis is notthe same as chemical or physical equilibrium. Suchequilibrium occurs when no net change is occurring: add milk to the co±ee and eventually, whenequilibrium is achieved, there will be no net di±usion of milk in the co±ee mug. Homeostasis, however, isthe process by which internal variables, such as body temperature, blood pressure, etc., are kept within arange of values appropriate to the system. When a stimulus changes one of these internal variables, itcreates a detected signal that the body will respond to as part of its ability to carry out homeostasis.HOMEOSTASISHomeostasis is the tendency of biological systems to maintain relatively constant conditions in theinternal environment while continuously interacting with and adjusting to changes originating within oroutside the system.Consider that when the outside temperature drops, the body does not just “equilibrate” with (become thesame as) the environment. Multiple systems work together to help maintain the body’s temperature: weshiver, develop “goose bumps”, and blood (ow to the skin, which causes heat loss to the environment,decreases.Many medical conditions and diseases result from altered homeostasis. This section will review theterminology and explain the physiological mechanisms that are associated with homeostasis. We willdiscuss homeostasis in every subsequent system. Many aspects of the body are in a constant state ofchange—the volume and location of blood (ow, the rate at which substances are exchanged between cellsand the environment, and the rate at which cells are growing and dividing, are all examples. But thesechanges actually contribute to keeping many of the body’s variables, and thus the body’s overall internalconditions, within relatively narrow ranges. For example, blood (ow will increase to a tissue when thattissue becomes more active. This ensures that the tissue will have enough oxygen to support its higherlevel of metabolism.Maintaining internal conditions in the body is called homeostasis(from homeo-, meaning similar, and stasis,meaning standing still). The root “stasis” of the term “homeostasis” may seem to imply that nothing ishappening. But if you think about anatomy and physiology, even maintaining the body at rest requires a lotof internal activity. Your brain is constantly receiving information about the internal and externalenvironment, and incorporating that information into responses that you may not even be aware of, such asslight changes in heart rate, breathing pattern, activity of certain muscle groups, eye movement, etc. Any ofthese actions that help maintain the internal environment contribute to homeostasis.

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Term
Spring
Professor
Hossam

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