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Dr Mrs Padmaja R Desai
Professor & Head
Department of Physiology
D Y Patil Medical College Kolhapur
A state of balance
in the body
• homeo = same; stasis = standing
• Homeostasis is the term we use to describe the
constant state of the internal environment.
• The processes and activities
that help to maintain homeostasis are referred to as
• Maintenance of the constant condition in the
internal environment is called as Homeostasis
.This term was first introduced by Walter
• The temperature, PH, concentration of
various solutes and ions of ECF is almost
• The ECF forms the internal environment of
the cell or body is called as milieu interior
• .This term was first introduced by a French
Physiologist Claude Bernard
• Similarly the temperature, PH ,solute
concentration of intracellular fluid (ICF) is
• The enzyme systems in our body are very
sensitive to changes in temperature, pH and
ion concentration .
• Any deflection from the normal range will
affect their functioning. Enzymes are killed
and finally all the biological activities come to
stand still and death occur. eg temperature of
homeostasis is maintained with the co-
ordination of different organs.
Endocrine and Nervous system
• The endocrine system
initiates the action
slowly ,but the action
continues for longer
period of time.
• Where as the nervous
system action is faster
but it is immediately
• Many factors try to destabilize the internal
environment but there are large number of
control mechanisms in our body that try to
destabilize this forces and homeostasis is
• Negative Feedback Mechanism
• Positive Feedback Mechanism
Negative Feedback Mechanism
• Majority of the controlling mechanism in the
body are negative feedback mechanism .Here
the effector response is negative or opposite to
the initiating stimulus(disturbance).
• It leads to stability and is beneficial to our
components of a control system:
1. The Sensor which detects the stress.
2. The Control Center which receives information
from the sensor and sends a message to adjust the
3. The Effector which receives the message from the
control center and produces the response which
• e.g. 1) When the blood pressure rise or
lowers suddenly the Baroreceptor
Mechanism brings the blood pressure to
↑ BP leads to ↓BP
↓ BP leads to ↑ BP
• More the gain more effective is the system.
gain of blood pressure baroreceptor control system
• gain of temperature control system is -33.
• so the temperature control system is more effective
than blood pressure baroreceptor system.
• No control system is 100% effective.
Blood Glucose Level
controlled by Negative feedback
controlled by insulin secreted from the
islets of Langerhans in pancreas
meal Blood glucose
4. Regulation of body temperature
The external temperature varies during the day and from
season to season, sometimes by as much as 40oC, but the
human body temperature stays at about 37oC
This is achieved by sweating, vasodilation,
vasoconstriction, and shivering
If the body temperature rises, the sweat glands in the
skin are activated and secrete sweat on to the surface of
When the sweat evaporates, it takes heat from the body
and cools it down
The sweat gland
extracts sweat from
the blood and
passes it up the
duct to the skin
surface where it
much heat lost
If the body temperature rises, the
blood vessels in the skin dilate
(become wider) and allow more
blood to flow near the surface. The
heat loss from the blood through the
skin helps cool the circulating blood
little heat lost
If the body temperature falls. The
blood vessels in the skin constrict.
Less warm blood flows near the
surface so less heat is lost
Vasoconstriction & dilation
Positive Feedback Mechanism:
• Here the effector response is same as that of
• This mechanism causes a vicious circle that
leads to instability and death.
There are very few positive feedback mechanism in our
body that are useful or beneficial to our body.eg
1) Blood Clotting:
2) Child Birth:
3) Generation of nerve impulse is another e.g. of
positive feed back, means development of AP and
spread of AP
4) Preovulatory LH surge
complex control systems
• Feed forward control system.
• Servo mechanism.
• Anticipatory control.
• Variable gain.
1. Text book of Medical Physiology
-Guyton & Hall, 12th edition.
2. Ganong’s review of Medical Physiology
- 23rd edition.
3. Text book of Medical Physiology
- 2nd edition
4. Net sources ( Acknowledge for all online source)
5. Text book of Medical Physiology
- Prof. A.K.Jain