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© SSER Ltd.
Homeostasis
In 1843, Claude Bernard embarked on a career in medicine and went on to become one of the leading
physiologists of the nineteenth century
During his years of research, Bernard was impressed by the stability of many physiological parameters,
and in 1859 he concluded that:
“It is the fixity of the internal environment which is the condition of free and independent life ……..All the vital mechanisms, however varied they may be,
have only one object, that of preserving constant the conditions of life in the internal environment.”
Homeostasis
The work of Claude Bernard provided the foundation for many further studies relating to the mechanisms
by which the body maintains internal constancy
In 1929, Walter Cannon, an American physiologist, coined the term ‘Homeostasis’ to describe the ability of the body to maintain a constant internal environment
The concept of homeostasis, as described by Bernard and Cannon, has continued to be the subject of much
intensive research as it pervades every aspect of the physiological mechanisms of life
Homeostasis is essential for the maintenance of life
Homeostasis
Homeostasis is the maintenance of a constant internal environment despite
fluctuations in both the body’s activities and the external environment
Various body systemswork cooperatively to
ensure that the composition of the
blood and tissue fluid remains within tolerable limits
Such homeostatic controls ensure that factors such as blood pH,
temperature and water potential, are kept within normal limits
Cellular biochemical reactions are controlled by enzymes whose activity is affected by fluctuating
temperature and pH levelsUnchecked water potentials in the blood and tissue fluids would result in inappropriate
entry or loss of water from cells and cellular disruption
Homeostasis Mechanisms
Homeostasis is usually achieved by a process called negative feedback
Negative feedback mechanisms involve:
• Deviation of a factor from its normal value or ‘set point’
• Receptors that detect any deviations from the norm
• Effectors that are activated by the receptors and correct the deviation by mechanisms that restore the norm
deviation from the
norm (excess)
deviation from the
norm (deficiency)
detected by receptors
detected by receptors
restoration of the norm(negative feedback)
restoration of the norm(negative feedback)
effectors stimulated and initiate corrective
mechanisms
effectors stimulated and initiate corrective
mechanisms
Negative feedback mechanismsare essential for the maintenanceof a stable internal environment
Control of body core temperature Control of
blood pH
Control of blood osmotic potential
Control of blood glucose level
Control of ion concentrations in the blood (e.g. calcium,
sodium and potassium ions)
A knowledge of homeostasis, and its importance in sustaining life, has enabled humans to
explore inhospitable environments
Acknowledgements
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