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Ben Whitten


What is homeostasis?

Homeostasis is defined as the processes involved in maintaining a constant internal environment, within tolerance limits, despite changes in the internal and external environment. Tolerance limits simply reference a steady state in cells, and therefore organisms.

Homeostasis involves many different systems in multicellular organisms, however it mainly involves:

  • The nervous system which is short lasting but provides fast responses, and

  • The endocrine system which is long lasting but there is a response lag

What are the main factors which need to be kept within a range?

A number of factors must be kept within a range of tolerance limits, otherwise this may cause some harm to the organism. These factors include:

  • Water and dissolved ions

  • pH levels of tissues and/or blood fluids

  • Gases (carbon dioxide)

  • Blood glucose levels

  • Blood pressure

  • Temperature

Topic Menu
The Nervous System
The Endocrine System
Tolerance Limits
Effects of Tolerance Limit Deviation
Types of Adaptations
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How does homeostatic control occur?

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There are two stages to homeostatic regulation, where one is the detection of a change from a stable state (otherwise known as the stimulus), and the second stage is the response to the stimulus which usually counteracts the change.

Therefore, to understand homeostatic regulation, a stimulus-response model can be used. The purpose of homeostatic regulation is to maintain internal factors around a set normal value, and when the factors deviate away from the value, homeostatic adaptations will attempt to bring the factor back to the normal value.

The main components of a stimulus-response model include:

  • Stimulus

  • Receptor

  • Modulator (or control centre)

  • Effector

  • Response

  • Feedback

What is the role of enzymes in homeostasis?

Living organisms carry out a series of chemical reactions in order to continue living. A linked series of these reactions is collectively termed a biochemical pathway, and the sum of these reactions is called metabolism.

The metabolic reactions are controlled by enzymes, and without them, these reactions would be too slow to continue life. Enzymes are reusable biological catalysts which act by lowering the activation energy of chemical reactions, enabling them to proceed faster.

Enzymes are classed as proteins (however, some are ribosomes!) which are highly sensitive to factors such as temperature and pH level, and they have certain tolerance limits within which they can avoid denaturation and function effectively. When an enzyme becomes denatured, it is rendered useless as it changes shape and cannot carry out chemical reactions.

Protein shape in general is influenced by salinity, pH level, temperature and a number of different environmental factors. Homeostatic processes aid in maintaining these factors within tolerance limits for enzymes.

The key takeaway from this is that homeostasis is a necessity for survival.