Control System in Biology - A Look at Regulators and Control Systems

Regulators are the organisms that can regulate their own internal environment. They are present over a wide range of environment and habitats. The non-regulator organisms tend to confine to environments which are more stable such oceans or lakes, examples of non-regulators are algae and cnidarians. The mechanisms of regulations found in living organisms have many features in common with the mechanisms of regulations used in machines. The basic components of any control system are summarized in this figure. 

 basic components of control system

Any change from the set point activates the control system and returns condition towards the optimum level. When a mechanism is controlled by its own production it is called feedback mechanism. It is of two types

1. Negative feedback

2. Positive feedback

 

1.    Negative feedback: It is associated with increasing the stability of systems e.g. thermostat. In the electric oven the control system includes an effector (an input) and output (the oven temperature and a thermostat) which can be set to a desired level, the set point.

The thermostat acts as a detector (or receptor) and a regulator. The stimulus is heat. If the thermostat is set to reach 150 degree Celsius and electric current will provide the source of heat which will flow until the temperature of the oven passes the set-point of 150 degree Celsius, then the thermostat will cut out and no more heat will be supplied to the oven. When the temperature of the oven falls below 150 degree Celsius the thermostat will cut in again and the electric current will increase the temperature and restore the set-point. In this system the thermostat is functioning as an error detector where the error is the difference between the output (the heating element) being switched on or off. This is an example of steady-state negative feedback system which is typical of many of the physiological control mechanism found in organisms. 

The Control Of Thyroxine Production

The control of thyroxin production: This is a biological example of a simple control system. The production of thyroxin is controlled by thyroid releasing hormone or factor (TRH), and thyroid stimulating hormone (TSH). The figure illustrates the role of negative feedback in the control of thyroxin release by the thyroid gland. In this example the detector is the hypothalamus, the regulator is the pituitary gland and the effector is the thyroid gland.

12. Positive Feedback: It is rare in biological systems since it leads to an unstable situation and extreme states. During labor when the hormone oxytocin stimulates muscular contractions of the uterus, which in turn stimulate the release of more oxytocin.

Importance of feedback mechanism: It helps the proper functioning of the body machinery. Biological negative feedback mechanisms include the control of (a) Oxygen and CO₂ levels in the blood by controlling rate of breathing (b) rate of heart beat (c) blood pressure (d) hormone level (e) water balance for the regulation of pH (f) body temperature. These show the importance of a negative feedback mechanism for existence of an animal.