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Homeostasis by Dr.Mrs. Padmaja R Desai

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This ppt is for I MBBS Students.

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Homeostasis by Dr.Mrs. Padmaja R Desai

  1. 1. Homeostasis Dr Mrs Padmaja R Desai Professor & Head Department of Physiology D Y Patil Medical College Kolhapur
  2. 2. Homeostasis A state of balance in the body Whoa
  3. 3. • 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 homeostatic mechanisms.
  4. 4. • Maintenance of the constant condition in the internal environment is called as Homeostasis .This term was first introduced by Walter Bradford Cannon.
  5. 5. • The temperature, PH, concentration of various solutes and ions of ECF is almost constant. • 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
  6. 6. • Similarly the temperature, PH ,solute concentration of intracellular fluid (ICF) is almost constant
  7. 7. Significance • 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 ECF,BSL
  8. 8. homeostasis is maintained with the co- ordination of different organs. • ECF • LUNGS • GIT • LIVER • KIDNEYS
  9. 9. 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 switched off.
  10. 10. • 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 maintained. • Negative Feedback Mechanism • Positive Feedback Mechanism
  11. 11. 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 body.
  12. 12. Rise above normal value Fall below normal value normal value Corrective Mechanism Corrective Mechanism NEGATIVE FEEDBACK MECHANISM normal value negative feedback negative feedback
  13. 13. 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 stress. 3. The Effector which receives the message from the control center and produces the response which reestablishes homeostasis
  14. 14. • e.g. 1) When the blood pressure rise or lowers suddenly the Baroreceptor Mechanism brings the blood pressure to normal levels. ↑ BP leads to ↓BP ↓ BP leads to ↑ BP
  15. 15. “Gain” of a Control System.
  16. 16. • More the gain more effective is the system. gain of blood pressure baroreceptor control system is -2 • 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.
  17. 17. 2.Regulation of Blood Glucose Level  controlled by Negative feedback mechanism  controlled by insulin secreted from the islets of Langerhans in pancreas
  18. 18. Liver converts glycogen to glucose normal blood glucose level Blood glucose level falls Soon after a meal Long after a meal Blood glucose level rises normal blood glucose level Too High Too Low Pancreas secretes insulin Pancreas secretes less insulin Liver coverts glucose to glycogen
  19. 19. 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 the skin When the sweat evaporates, it takes heat from the body and cools it down 5
  20. 20. sweat pore evaporation epidermis dermis sweat duct sweat gland blood vessel Section through skin The sweat gland extracts sweat from the blood and passes it up the duct to the skin surface where it evaporates 0.25 mm 6
  21. 21. much heat lost Vasodilation 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 Vasoconstriction 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 7
  22. 22. Positive Feedback Mechanism: • Here the effector response is same as that of initial stimulus. • This mechanism causes a vicious circle that leads to instability and death.
  23. 23. 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
  24. 24. Child Birth:
  25. 25. Development of AP and spread of AP
  26. 26. complex control systems • Feed forward control system. • Servo mechanism. • Anticipatory control. • Variable gain. • Coupling.
  27. 27. References 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

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