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Biochem www.latrobe.edu.au

Chapter 1: Homeostasis; some general principles.


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WHAT IS HOMEOSTASIS?

Homeostasis is the maintenance of a constant internal environment (the immediate surroundings of cells) in response to changes in:


Homeostasis is a self adjusting mechanism involving feedback where the response to a stimulus alters the internal conditions and may itself become a new stimulus.

Homeostasis works to maintain the organism's internal environment within tolerance limits - the narrow range of conditions where cellular processes are able to function at a level consistent with the continuation of life.

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HOW IS HOMEOSTASIS ACHIEVED?

To maintain cells, tissues and entire organisms within their biological tolerance limits, various mechanisms have evolved. These may be

Homeostasis is really the combined result of all of these, a failure of any one of them can result in the death of an individual. For now, we will focus on functional mechanisms of homeostasis, but students should not consider that these in isolation will maintain life.

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FEEDBACK MECHANISMS

Feedback mechanisms are the general mechanism of nervous or hormonal regulation in animals. Essentially, feedback occurs when the response to a stimulus has an effect of some kind on the original stimulus. The nature of the response determines how the feedback is 'labelled'.

Negative feedback is when the response diminishes the original stimulus.
Positive feedback is when the response enhances the original stimulus.

Negative feedback is most common in biological systems. Examples of this are:

Positive feedback is less common, which is understandable, as most changes to steady state pose a threat, and to enhance them would be most unhelpful. However, there are a few examples:

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FEEDBACK LOOPS

Regardless of whether the feedback is positive or negative, feedback mechanisms have certain essential components. Students should be able to identify each of these and explain their role.

These feedback loops, as they are often called, are usually well illustrated in textbooks. Check yours for examples, or click here to see some feedback loop diagrams.

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This page is maintained by Jenny Herington, who can be contacted at bio_cat@bioserve.latrobe.edu.au by email, Last update :14 March 97