Homeostasis refers to the maintenance of a stable internal environment in the body. It involves negative feedback loops that counteract changes to keep properties like temperature and pH levels within normal ranges. The concept of homeostasis was introduced by Walter Cannon in 1930 and forms the basis of physiology. It works through a cyclical system of receptors that detect changes, a control center that activates effectors to correct deviations and restore balance. Most processes use negative feedback loops while some emergency responses employ positive feedback. Disruptions to homeostasis can cause illness.

1. HOMEOSTASIS

2. “Homeostasis /Introduction ”
“ ‘Homeostasis’ refers to the maintenance of constant internal
environment of the body (homeo = same; stasis = standing).
Importance of internal environment was notified by the great biologist
of 19th century Claude Bernard.
Internal environment in the body is the extracellular fluid (ECF) .
The word ‘homeostasis’ was introduced by Harvard Professor, Walter B
Cannon in 1930.The concept of homeostasis forms the basis of
physiology .
A Text Book of Physiology By PR Ashalata G Deepa 4TH edition

3. Definition
Homeostasis is the tendency to resist change in order to maintain a
stable, relatively constant internal environment.
Homeostasis typically involves negative feedback loops that
counteract changes of various properties from their target values,
known as set points.
In contrast to negative feedback loops, positive feedback
loops amplify their initiating stimuli, in other words, they move the
system away from its starting state.

4. Importance of homeostasis
ECF contains nutrients, ions and all other substances necessary for the
survival of the cells.
Normal healthy living of large organisms including human beings
depends upon the constant maintenance of internal environment within
the physiological limits.
If the internal environment deviates beyond the set limits, body
suffers from malfunction or dysfunction.
The concept of homeostasis forms basis of physiology .
Understanding the concept of homeostasis also forms the basis for
clinical diagnostic procedures.

5. Components of homeostatic System
 The homeostatic system is a self-regulating mechanism that occurs in
a cyclical pattern. It has the following three components;
 Receptors: These recognize any deviation from normal level of
physiological parameters and provide feed back to control center.
 Control Centre : Receives information about variation in
physiological parameters from receptors and activate the effector
system.
Effectors: these receives the information from the control center and
correct the deviation.

6. Components of homeostatic System
Receptors Control Centre Effectors

8. Mechanism of action of homeostatic System
The homeostatic System acts through feedback mechanism . It is a
process in which some proportion of output signal of a system is fed
(passed ) back to the input. There are two types of feedback
mechanism.
Negative feedback mechanism.
Positive feedback mechanism.

9. Negative feedback mechanism.
Negative feedback is the one , to which the system reacts in such a
way so, as to arrest the change or reverse the direction of change .
 After receiving a message , the effectors send the negative feedback
signals back to the system.
 Now the system stabilizes its own function and makes an attempt to
maintain homeostasis.
Most of the homeostatic mechanism in the body function through
negative feedback, for example , ACTH and Cortisol secretion.

10. Negative feedback mechanism.

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14. Positive feedback
Positive feedback is the one to which the system reacts in such a way
as to increase the intensity of the change in the same direction.
Positive feedback is less common than the negative feedback.
However, it has its own significance particularly during emergency
conditions.
Example of positive feedback mechanism include;
Child Labor /Parturation/Delivery
Blood Clotting
Ovulation

16. Positive feedback
One of the positive feedbacks occurs during the blood clotting.
Blood clotting is necessary to arrest bleeding during injury and it occurs
in three stages.
The three stages are:
 Formation of prothrombin activator
 Conversion of prothrombin into thrombin
 Conversion of fibrinogen into fibrin.

19. Summary
Tendency to resist change in order to maintain a stable, relatively constant internal
environment is called Homeostasis .
The word ‘homeostasis’ was coined by Walter B Cannon in 1930.
The homeostatic system is a self-regulating mechanism that occurs in a cyclical
pattern. It has three components i.e. Receptor, Control Centre and Effectors.
The homeostatic System acts through feedback mechanism . It is a process in
which some proportion of output signal of a system is fed (passed ) back to the
input. There are two types of feedback mechanism ;Negative feedback
mechanism And Positive feedback mechanism.
Most of the Physiological Process are regulated through positive feedback such as
homeostasis of plasma glucose level.
Homeostasis forms basis of physiology as well as helps to form basis for
diagnostic procedure.
If the internal environment deviates beyond the set limits, body suffers from
malfunction or dysfunction.

20. References
A Text Book Anatomy and of Physiology By PR Ashalata G Deepa
4TH edition.
Essential of Physiology 6th Edition By Sk and Prema Simbulangum
Wwww.slideshare.com
www.google.com