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2. 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.”

3. 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

4. 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

5. Various body systems work 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 levels Unchecked water potentials in the blood and tissue fluids would result in inappropriate entry or loss of water from cells and cellular disruption

6. 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

7. deviation from the norm (excess) deviation from the norm (deficiency) detected by receptors restoration of the norm (negative feedback) restoration of the norm (negative feedback) effectors stimulated and initiate corrective mechanisms

9. Negative feedback mechanisms are essential for the maintenance of a stable internal environment

10. 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)

11. A knowledge of homeostasis, and its importance in sustaining life, has enabled humans to explore inhospitable environments

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