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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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