Homeostasis
The word homeostasis describes the body’s ability to maintain relatively stable internal conditions even though the outside world is continuously changing. Although the literal translation of homeostasis is “unchanging” (homeo = the same; stasis = standing still), the term does not really mean an unchanging state. Instead, it indicates a dynamic state of equilibrium, or a balance in which internal conditions change and vary but always within relatively narrow limits.
1.6.1 Homeostatic Controls
Homeostasis in the human body is continually being disturbed. Some disruptions come from the external environment in the form of physical insults such as the intense heat of a hot summer day or a lack of enough oxygen for that two-mile run. Other disruptions originate in the internal environment, such as a blood glucose level that falls too low when you skip breakfast.
1.6.1.1 Feedback Systems
The body can regulate its internal environment through many feedback systems. A feedback system or feedback loop is a cycle of events in which the status of a body condition is monitored, evaluated, changed, remonitored, reevaluated, and so on. Each monitored variable, such as body temperature, blood pressure, or blood glucose level, is termed a controlled condition. Any disruption that changes a controlled condition is called a stimulus. A feedback system includes three basic components: a receptor, a control center, and an effector.
- A receptor is a body structure that monitors changes in a controlled condition and sends input to a control center.
- A control center in the body, for example, the brain, sets the range of values within which a controlled condition should be maintained (set point), evaluates the input it receives from receptors, and generates output commands when they are needed.
- An effector is a body structure that receives output from the control center and produces a response or effect that changes the controlled condition.
Figure 3- The elements of a homeostatic control system
There are two types of Feedback Systems
i. Negative Feedback System
ii. Positive Feedback System
i. Negative Feedback System
In Negative Feedback System, the net effect of the response to the stimulus is to shut off the original stimulus or reduce its intensity.
ii. Positive Feedback System
In Positive feedback systems are rare in the body because they tend to increase the original disturbance (stimulus) and to push the variable farth from its original value.