=Homeostasis= Homeostasis is the ability of certain systems to maintain a relatively constant internal environment in spite of changes in external conditions. For instance, in humans, there are tightly regulated control systems that regulate our: * Body temp * Osmolarity (including salinity / ion conc) * pH * Blood glucose levels * Blood Oxygen Saturation ==Feedback mechanisms== Most homeostatic control systems adjust internal conditions to compensate for changes caused by the external environment. This is often referred to as a negative feedback loop. [image:http://i.imgur.com/FDcij4kl.png] 1. '''Stimulus''' - A disruption to the internal environment usually resulting from changes in external conditions. E.g. a slight decrease in body temperature resulting from a cooler external environment. 2. '''Receptors''' - Components of the control systems that detect changes to the internal environment. E.g. nerve endings in the skin and hypothalamus can sense changes in temperature. 3. '''Control Centre''' - Signals from the receptors are usually sent to a control centre that processes messages from multiple receptors in order to determine what an appropriate response might be. For instance the Hypothalamus in our brains processes signals from central and peripheral thermoreceptors before signalling effectors to initiate a response. The control centre usually determines our ''set point'' and will signal effectors to compensate for any deviation from this. For instance the hypothalamus normally works to maintain a set point core temperature of 37°C. 4. '''Effectors''' - Components of the regulatory system that can adjust the body's internal environment. They are used to restore the internal environment to the set point. For instance the effectors used in thermoregulation are the componenets of the system that can raise or lower our body temperature (e.g. our muscles that contract when we shiver). 5. '''Response''' - The action of the effectors which is to adjust the internal environment, usually restoring it to the set point. E.g. shivering generates heat and and can be used to raise our core body temperature back to a set point of approximately 37°C.
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