The composition of the internal environment is tightly controlled,and this fairly constant state is called homeostasis. Literally,this term means ‘unchanging’ but in practice it describes a dynamic,ever-changing situation kept within narrow limits. When this balance is threatened or lost,there is a serious risk to the well-being of the individual.
HOMEOSTASIS is maintained by control systems that detect and respond to changes in the internal environment. A control system has three basic components : detector,control center and effector.
The control center determines the limits within which the variable factor should be maintained. It receives an input from the detector ,or sensor,and integrates the incoming information. When the incoming signal indicates that an adjustment is needed,the control center responds and it’s output to the effector is changed. This is a dynamic process that allows constant readjustment of many physiological variables.
NEGATIVE FEEDBACK MECHANISMS.
In systems controlled by negative feedback,the effector response decreases or negates the effect of the original stimulus,maintaining or restoring homeostasis(thus the term negative feedback.
POSITIVE FEEDBACK MECHANISMS.
There are only a few of these cascade or amplifier systems in the body. In positive feedback mechanisms,the stimulus progressively increase the response,so that as long as the stimulus is controlled the response is progressively amplified. Examples include blood clotting and uterine contractions during labour.
