Chapter 12.1- Principles of homeostasis
What is homeostasis?
Homeostasis is the maintenance of constant internal environment in organisms. It involves
maintaining the chemical make-up, volume and other features of blood and tissue fluid within
restricted limits. Homeostasis ensures that the cells of the body are in an environment that meets
their needs and allows them to function normally despite external changes. This does not mean that
there are no changes. On the contrary, there are continuous fluctuations brought about by
variations in internal and external conditions, such as changes in pH, temperature and water
potential. These changes, however, occur around a set point. Homeostasis is the ability to return to
that set point and so maintain organisms in a state of equilibrium.
The importance of homeostasis
Homeostasis is essential for the proper functioning of organisms for the following reasons:
The enzymes that control biochemical reactions within cells and other proteins such as
channel proteins are sensitive to changes in both pH and temperature. Any changes to these
factors reduce the efficiency of enzymes or can even denature them, stopping them from
working altogether. Even small fluctuations in temperature or pH can impair the ability of
enzymes to carry out their roles effectively. Maintaining a constant internal environment
means that reactions take place at a constant and predictable rate.
Changes to water potential of the blood and tissue fluids may cause cells to shrink or expand
(so much they may even burst) as a result of water leaving or entering by osmosis. In both
instances the cells cannot operate normally. The maintenance of a constant blood glucose
concentration is essential in ensuring a constant water potential. A constant blood glucose
concentration also ensures a reliable source of glucose for cells to use during respiration.
Organisms with the ability to maintain a constant internal environment are more
independent of the external environment. They have a wider geographical range and
therefore have a greater chance of finding food, shelter etc. Mammals, for example, with
their ability to maintain a constant temperature, are found in most habitats, ranging from
hot arid deserts to cold, frozen Polar Regions.
Control mechanisms
The control of any self-regulating system involves a series of stages that feature:
The set point – This is the desired level, or norm at which the system operates. This is
monitored by a:
Receptor – which detects any deviation from the set point and informs the…
Controller – which coordinates information from various receptors and sends instructions to
an appropriate…
Effector – which brings about the changes needed to return the system to the set point. This
return to normality creates a …
Feedback loop – which informs the receptor of the changes to the system brought about by
the effector.
Coordination of control mechanisms
Systems usually have many receptors and effectors. It is important to ensure that the information
provided by receptors is analysed by the control centre before any action is taken. Receiving
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What is homeostasis?
Homeostasis is the maintenance of constant internal environment in organisms. It involves
maintaining the chemical make-up, volume and other features of blood and tissue fluid within
restricted limits. Homeostasis ensures that the cells of the body are in an environment that meets
their needs and allows them to function normally despite external changes. This does not mean that
there are no changes. On the contrary, there are continuous fluctuations brought about by
variations in internal and external conditions, such as changes in pH, temperature and water
potential. These changes, however, occur around a set point. Homeostasis is the ability to return to
that set point and so maintain organisms in a state of equilibrium.
The importance of homeostasis
Homeostasis is essential for the proper functioning of organisms for the following reasons:
The enzymes that control biochemical reactions within cells and other proteins such as
channel proteins are sensitive to changes in both pH and temperature. Any changes to these
factors reduce the efficiency of enzymes or can even denature them, stopping them from
working altogether. Even small fluctuations in temperature or pH can impair the ability of
enzymes to carry out their roles effectively. Maintaining a constant internal environment
means that reactions take place at a constant and predictable rate.
Changes to water potential of the blood and tissue fluids may cause cells to shrink or expand
(so much they may even burst) as a result of water leaving or entering by osmosis. In both
instances the cells cannot operate normally. The maintenance of a constant blood glucose
concentration is essential in ensuring a constant water potential. A constant blood glucose
concentration also ensures a reliable source of glucose for cells to use during respiration.
Organisms with the ability to maintain a constant internal environment are more
independent of the external environment. They have a wider geographical range and
therefore have a greater chance of finding food, shelter etc. Mammals, for example, with
their ability to maintain a constant temperature, are found in most habitats, ranging from
hot arid deserts to cold, frozen Polar Regions.
Control mechanisms
The control of any self-regulating system involves a series of stages that feature:
The set point – This is the desired level, or norm at which the system operates. This is
monitored by a:
Receptor – which detects any deviation from the set point and informs the…
Controller – which coordinates information from various receptors and sends instructions to
an appropriate…
Effector – which brings about the changes needed to return the system to the set point. This
return to normality creates a …
Feedback loop – which informs the receptor of the changes to the system brought about by
the effector.
Coordination of control mechanisms
Systems usually have many receptors and effectors. It is important to ensure that the information
provided by receptors is analysed by the control centre before any action is taken. Receiving
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