Walter B. Cannon (1871-1945), an American physiologist, was the person that coined the term homeostasis in 1932 (Clancy, J, McVicar, A, 2002).
Cannon observed that each body structure, from the very simple ones to the more complex mammals, had to contribute in some way to keep their internal balance. This internal environment is made by the following main components: tissue fluid, plasma and intracellular fluid (Hole Jr, 1993).
- Feedback mechanisms
Feedback mechanisms or loops consist of three basic components: a control centre, a receptor, and an effector (Martini, 2005).
The control centre is in charge of establishing which would be the controlled condition to be maintained. The controlled conditions are altered by a stimulus.
The receptor would monitor these changes brought by the stimulus and send the information to the control centre.
The control centre would then send a message to the effector, a cell or organ that would produce a response or effect.
There are two types of feedback control mechanisms: positive feedback and negative feedback (Martini, 2005).
If the responses maintain or enhance in any way the original stimulus this is called positive feedback control. This effect does not result in homeostasis, because it is not maintaining the equilibrium.
If the responses do the opposite and reverse the original stimulus this is called negative feedback control. Since this tends to keep things constant, it allows the maintenance of homeostasis.
- Thermoregulation in the human body
The human body is constantly gaining heat from metabolism and, in cold climates, losing heat to the environment. Under very hot conditions, the body may gain heat from the environment.
The human body is persistently trying to retain their organs at an optimal temperature.
Homeostasis plays a crucial part in controlling heat transfer across the skin. The hypothalamus, located in the lower part of the brain, controls various body activities of the nervous and endocrine systems, secretes hormones, and regulates the body temperature to an optimum 37°C. It is therefore seeing as the main regulator of homeostasis in the body (Clancy, McVicar, 2002)
On the one hand, if the temperature of the blood flow within the body falls beyond the optimum 37°C (controlled condition), the hypothalamus sends a message to the nervous system to stimulate activities that promote heat loss. These activities form part of a negative feedback system. Nerves impulses from the preoptic area of the hypothalamus (control centre) reset the body to carry out heat loss activities that include vasodilatation, stimulation of the secretory output and increase respiration (Tortora & Grabowski, 1996). These are considered the effectors that reverse the stimulus in the negative feedback loop.
- Vasodilatation is the process by which the blood flow goes to the surface of the skin acquiring a reddish colour, and it is followed by radiation of heat to the external environment.
- Because of vasodilatation, the sweat glands would increase the production of secretory output by perspiration. This helps the body to evaporate heat.
- An increase of respiration through the mouth would then result in evaporation of heat coming from the lungs.
The response is the decrease in body temperature until the controlled condition is attained.
Negative feedback loop of Thermoregulation in the human body at high and low temperature exposure (Cummings, date not available)
On the other hand, if the temperature of the blood flow was lower than 37°C (controlled condition), the hypothalamus would then respond with a negative feedback loop able to promote heat retention and produce more heat. In order to increase body temperature the preoptic area acts as a thermostat (control centre) that prevents hypothermia and employs heat conservation and heat generation mechanisms (Martini, 2005).
The heat conservation mechanisms involve decreasing the blood flow to the skin in order to reduce radiation of heat to the external environment. The blood supply to the skin is restricted (effector) and makes it appear paler in colour though it does not damage skin cells. This supply is diverted to a network of veins that protects the vital organs from hypothermia by maintaining the controlled condition (Tortora & Grabowski, 1996).
The heat generation devices are divided in two categories: shivering thermogenesis and non-shivering thermogenesis (effectors).
- The shivering thermogenesis enhances the energy consumption of the skeletal muscle in the body producing more heat (response).
- The non-shivering thermogenesis works by releasing epinephrine hormone and thyrotropin releasing hormone (TRH). These hormones aim to enhance the metabolic activities of body tissues by increasing metabolic and catabolic rates within the body (response). The result is an increase in body temperature (response) to the set point of 37°C.
- Conclusion
Complex systems like the human body must embrace homeostasis in order to maintain stability and to survive. Their internal environment must have certain conditions within tolerable limits to continue the healthy functioning. In the case of Thermoregulation, the controlled condition is the body temperature.
The human body is an incredible organism able to adapt and evolve according to the changes of the environment even though these changes may be extreme. Negative feedback systems can keep that oscillation at a minimum and ensure that the human body is protected against unpredictable alterations from the external environment.
- REFERENCES LIST
Clancy, J, McVicar, A (2002) Physiology and Anatomy – A Homeostatic Approach Second Edition London: Arnold Publisher
Cummings, B (date not available) Homeostasis - body temperature Available from: http://fig.cox.miami.edu/~cmallery/150/physiol/c44x10thermo-reg.jpg Pearson Education Inc
Hole Jr, J (1993) Human Anatomy and Physiology Sixth Edition England: WM. C. Brown Communication Inc
Martini, FH (2005) Fundamentals of Anatomy and Physiology Seventh Edition San Francisco: Pearson Education Inc
Tortora, G, Grabowski, S (1996) Principles of Anatomy and Physiology Eighth Edition New York: Harper Collins Publishers Inc.
