HOMEOSTASISDr Nilesh N KateAssociate ProfessorESIC Medical College.Gulbarga.

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.

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.

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.

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%

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.

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

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

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.

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.

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.

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.

CARDIOVASCULAR SYSTEM Transports oxygen, carbondioxide, nutrients

and hormones to and from the body cells.

Helps regulate pH and temperature.

Provides protection against diseases.

RESPIRATORY SYSTEM

Exchange the gases between atmospheric air and blood.

Help adjust the pH of the body fluids.

NERVOUS SYSTEM

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

ENDOCRINE SYSTEM

Regulates the activity and growth of target cells in the body.

Regulate metabolism

GASTROINTESTINAL SYSTEM

Breaks down food into absorbable form.

Absorbs various nutrients.

Eliminates waste from the body.

EXCRETORY SYSTEM Helps eliminate the waste products from the

body.

Maintains the blood pH, volume, pressure, osmolarity, electrolyte composition etc.

Produces hormones.

SKELETAL SYSTEM Bones provide support, protection, the

production of blood cells.

Muscles produce body movements and produce heat to maintain the body

temperature.

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.

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.

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.

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

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.

A FEEDBACK LOOP

NEGETIVE FEEDBACK Mechanisms that maintain the factor at some

mean value. Reverse a change Restore abnormal values to normal

NEGATIVE FEEDBACK LOOPNEGATIVE FEEDBACK LOOP

EXAMPLE: NEGATIVE FEEDBACKEXAMPLE: NEGATIVE FEEDBACKBLOOD PRESSURE REGULATIONBLOOD PRESSURE REGULATION

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.

POSITIVE FEEDBACK LOOPPOSITIVE FEEDBACK LOOP

EXAMPLE: POSITIVE FEEDBACKEXAMPLE: POSITIVE FEEDBACKMEMBRANE DEPOLARISATIONMEMBRANE DEPOLARISATION

POSITIVE FEEDBACKS IN BODY Action potential Clotting of blood Parturition Release of calcium

from SR Sexual arousal LH surge

NEGATIVE Vs POSITIVE FEEDBACK

EFFECTIVENESS OF A FEEDBACK CONTROLTHE PRINCIPLE OF GAIN

GAIN = Correction/ErrorHigher 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

FINAL OUTCOME OF HOMEOSTATIC PROCESSES