This document discusses homeostasis, which refers to the maintenance of stable internal conditions in the body despite changes in the external environment. It describes how unicellular organisms evolved internal environments as multicellular organisms developed. The human body maintains homeostasis through various organ systems that cooperate via feedback mechanisms to keep conditions like temperature, pH, electrolyte levels, and oxygen/carbon dioxide levels within normal ranges. Homeostatic control mechanisms can involve negative or positive feedback loops to restore the body's normal state when disturbed.

1. HOMEOSTASIS
Dr Nilesh N Kate
Associate Professor
ESIC Medical College.
Gulbarga.

2. WHAT HAPPENS IF THERE IS A CHANGE IN OUR
ENVIRONMENT?
 Depending upon the
degree of change:
 Discomfort
 Disease/sickness
 Damage/injury
 Death
 So any significant change
in the environment is
harmful for an organism.

3. LIFE ORIGINATED AS UNICELLULAR ORGANISMS
IN PRIMITIVE SEA
 The primitive sea was the
environment for the primitive
unicellular organisms.
 They obtained nutrition from it
and discharged wastes in it.
 The vastness of the sea kept its
composition almost constant.

4. UNICELLULAR ORGANISMS EVOLVED INTO
MUTLICELLULAR ORGANISMS
 Some cells in multicellular
organisms were away from
the primitive sea.
 As cells could not reach the
sea, the sea was brought
within in the form of
extracellular fluid.

5. 60% OF HUMAN BODY IS WATER!
 40% is intracellular fluid (ICF)
i.e. fluid inside the cells.
 20% is extracellular fluid
(ECF) i.e. fluid outside the
cells. Further divided into:
 Interstitial Fluid (ISF)- 15%
 Plasma- 5%

6. ECF: THE INTERNAL ENVIRONMENT OF
THE BODY
 All the cells in the body live in
the same environment, the ECF.
 So, the ECF is also k/a ‘internal
environment’ of the body or
‘milieu intérieur’
 They get nutrition from it &
discharge their waste products
in it.

7. milieu intérieur A TERM COINED BY
Claude Bernard
 French physiologist.
 Father of physiology.
 “La fixit du milieu intkrieur est
fa condition de fa vie fibre.”
(the constancy of the
internal environment is
necessary for free life).
1813-1878

8. Walter B. Canon NAMED THE FIXITY DESCRIBED BY
Bernard AS ‘Homeostasis’
 American physiologist.
 Coined the term ‘homeostasis’.
 Described homeostasis as- ‘an
evolutionary development of a
metabolic wisdom that provides
for internal constancy’.
1871-1945

9. HOMEOSTASIS
 ‘maintenance of nearly
constant conditions in the
internal environment’.
 ‘the various physiologic
arrangements which serve
to restore the normal state,
once it has been disturbed’
are known as Homeostatic
Mechanisms.

10. WHAT NEEDS TO BE MAINTAINED CONSTANT IN
INTERNAL ENVIRONMENT?
1. Concentration of oxygen
and carbon dioxide.
2. pH of the internal
environment.
3. Concentration of
nutrients and waste
products.
4. Concentration of salt
and other electrolytes.
5. Volume and pressure of
extracellular fluid.

11. HOMEOSTASIS: AS DESCRIBED BY CANON
 perturbation in the organism’s steady state may arise from
changes within the organism as well as changes from without.
 homeostasis is not the responsibility of a single system but that
all the organ systems of the body operate cooperatively to effect
internal constancy.
 each cell benefits from homeostasis, and in turn, each cell
contributes its share toward the maintenance of homeostasis.
 the more “advanced” the evolutionary stage of a particular group
or organisms, the more subtle and complex the homeostatic
apparatus.

12. ALL ORGANS AND ORGAN SYSTEMS OF THE BODY HELP
IN MAINTENANCE OF HOMEOSTASIS
 Cardiovascular system.
 Respiratory system.
 Nervous system.
 Endocrine system.
 Gastrointestinal system.
 Excretory system.
 Skeletal system.
 Integumentry system.
 Reproductive system.

13. CARDIOVASCULAR SYSTEM
 Transports oxygen, carbondioxide, nutrients
and hormones to and from the body cells.
 Helps regulate pH and temperature.
 Provides protection against diseases.

14. RESPIRATORY SYSTEM
 Exchange the gases between atmospheric air
and blood.
 Help adjust the pH of the body fluids.

15. NERVOUS SYSTEM
 Generates nerve
impulses (Action
Potential) that provide
communication and
regulation of most
body tissues.

16. ENDOCRINE SYSTEM
 Regulates the activity and growth of target
cells in the body.
 Regulate metabolism

17. GASTROINTESTINAL SYSTEM
 Breaks down food into absorbable form.
 Absorbs various nutrients.
 Eliminates waste from the body.

18. EXCRETORY SYSTEM
 Helps eliminate the waste products from the
body.
 Maintains the blood pH, volume, pressure,
osmolarity, electrolyte composition etc.
 Produces hormones.

19. SKELETAL SYSTEM
 Bones provide support, protection, the
production of blood cells.
 Muscles produce body movements and
produce heat to maintain the body
temperature.

20. INTEGUMENTARY SYSTEM
 Contributes to homeostasis by protecting the
body and helping regulate the body
temperature. It also allows you to sense
pleasurable, painful and other stimuli in your
external environment.

21. REPRODUCTIVE SYSTEM
 Sometimes reproduction is not considered a
homeostatic function.
 Helps maintain homeostasis by generating
new beings to take the place of those that are
dying and thus help in maintaining the
continuity of life.

22. HOW HOMEOSTATIC CONTROL MECHANISMS
WORK?
 Homeostatic control
mechanisms work
through ‘Feedback
Mechanisms’.
 Status of a body
condition is
continually monitored,
evaluated, changed, re-monitored
&
reevaluated.

23. FEEDBACK MECHANISM  A feedback mechanism is a cycle in which the
output of a system “feeds back” to either modify or
reinforce the action taken by the system.
 A feedback mechanism may operate at:
 Tissue level
 Organ level
 Organ system level
 Body level, integrating with other organ systems.
 Feedback mechanism can be:
 Negative feedback (more common)
 Positive feedback

24. A FEEDBACK SYSTEM CONSISTS OF THREE
COMPONENTS
1. SENSOR (RECEPTOR):
detects specific changes
(stimuli) in the environment.
2. INTEGRATOR: act to direct
impulses to the place where
a response can be made.
3. EFFECTOR: performs the
appropriate response.

25. A FEEDBACK LOOP

26. NEGETIVE FEEDBACK
 Mechanisms that maintain the factor at some
mean value.
 Reverse a change
 Restore abnormal values to normal

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29. POSITIVE FEEDBACK
 Strengthens or reinforces a change.
 Makes abnormal values more abnormal.
 Produces ‘Vicious Cycle’.
 But in body a mild degree of positive feedback can be
overcome by the negative feedback control
mechanisms of the body, and the vicious cycle fails to
develop.

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32. POSITIVE FEEDBACKS IN BODY
 Action potential
 Clotting of blood
 Parturition
 Release of calcium
from SR
 Sexual arousal
 LH surge

33. NEGATIVE Vs POSITIVE
FEEDBACK

34. EFFECTIVENESS OF A FEEDBACK CONTROL
THE PRINCIPLE OF GAIN
GAIN = Correction/Error
Higher the gain, more efficient is the system
Normal BP = 100 mm Hg
Some disturbance causes an ↑ BP = 175 mm Hg
Baroreceptor mechanism brings BP down to 125 mm Hg
So correction done by baroreceptor mechanism = - 50 mm Hg
But still error = 25 mm Hg
So, Gain = - 50/25 = - 2

35. FINAL OUTCOME OF
HOMEOSTATIC PROCESSES