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HOMEOSTASIS

HOMEOSTASIS

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HOMEOSTASIS

  1. 1. HOMEOSTASIS Dr Nilesh N Kate Associate Professor ESIC Medical College. Gulbarga.
  2. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 13. CARDIOVASCULAR SYSTEM  Transports oxygen, carbon dioxide, nutrients and hormones to and from the body cells.  Helps regulate pH and temperature.  Provides protection against diseases.
  14. 14. RESPIRATORY SYSTEM  Exchange the gases between atmospheric air and blood.  Help adjust the pH of the body fluids.
  15. 15. NERVOUS SYSTEM  Generates nerve impulses (Action Potential) that provide communication and regulation of most body tissues.
  16. 16. ENDOCRINE SYSTEM  Regulates the activity and growth of target cells in the body.  Regulate metabolism
  17. 17. GASTROINTESTINAL SYSTEM  Breaks down food into absorbable form.  Absorbs various nutrients.  Eliminates waste from the body.
  18. 18. EXCRETORY SYSTEM  Helps eliminate the waste products from the body.  Maintains the blood pH, volume, pressure, osmolarity, electrolyte composition etc.  Produces hormones.
  19. 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. 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. 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. 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. 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. 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. 25. A FEEDBACK LOOP
  26. 26. NEGETIVE FEEDBACK  Mechanisms that maintain the factor at some mean value.  Reverse a change  Restore abnormal values to normal
  27. 27. NEGATIVE FEEDBACK LOOP
  28. 28. EXAMPLE: NEGATIVE FEEDBACKEXAMPLE: NEGATIVE FEEDBACK BLOOD PRESSURE REGULATIONBLOOD PRESSURE REGULATION
  29. 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.
  30. 30. POSITIVE FEEDBACK LOOP
  31. 31. EXAMPLE: POSITIVE FEEDBACKEXAMPLE: POSITIVE FEEDBACK MEMBRANE DEPOLARISATIONMEMBRANE DEPOLARISATION
  32. 32. POSITIVE FEEDBACKS IN BODY  Action potential  Clotting of blood  Parturition  Release of calcium from SR  Sexual arousal  LH surge
  33. 33. NEGATIVE Vs POSITIVE FEEDBACK
  34. 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. 35. FINAL OUTCOME OF HOMEOSTATIC PROCESSES

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