GED Science Practice Test: Feedback Systems

Two of the most important functions of body systems and the cells within those systems are metabolism and homeostasis. Remember that metabolism includes any chemical process that occurs within or between cells that helps to sustain life.  These processes are typically thought of as breaking down large organic molecules to be used by the cell and/or building up larger organic molecules from their building blocks. Homeostasis is the regulation of variables within the internal environment of an organism so that they remain fairly constant, and stay in equilibrium, even when internal or external conditions might change. An example of homeostasis is temperature regulation in endothermic (warm-blooded) animals such as humans.

In order to understand how body systems work to regulate metabolism and control internal conditions via homeostasis, you need to understand feedback systems.  Feedback systems respond to a stimulus, a change in the environment, but either trying to revert the system back to normal, or to enhance the action of the stimulus.  Negative feedback systems try to revert the system back to normal. In real life, an example of a negative feedback system is a home thermostat.  If you set a thermostat at a certain temperature, say 70 degrees, and the temperature drops below 70 (the stimulus), the thermostat turns on the heat to bring the temperature back to its original temperature, 70 degrees.  In the human body, a good example of a negative feedback system is the regulation of blood sugar.  When the body senses an increase in blood sugar, like would happen after ingesting a meal, receptors in the blood send a message to the pancreas (part of the endocrine and digestive systems) to release the chemical, insulin.  Insulin effectively reduces the amount of sugar in the blood by moving it into your cells.  Most feedback systems in the human body are negative feedback systems.

Positive feedback systems try to maintain or increase the effects of a stimulus.  In real life, an example of a positive feedback system might be that the better work you do, the more you are praised by your boss, which leads you to do even better work.  An example of a positive feedback system in the human body is childbirth.  During childbirth, the body releases a hormone called oxytocin, which increases the speed and intensity of the contractions.  Increasing contractions cause more oxytocin to be released.

This simple diagram compares and contrasts positive and negative feedback systems:



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