1. Denny Agustiningsih Dept. of Physiology

2.  Concept of homeostasis was formulated by a French Physiologist Claude Bernard in 1865  He noticed that La fixité du milieu intérieur est la condition de la vie libre (it is the fixity of milieu intérieur which is the condition of free and independent life) WHAT IS HOMEOSTASIS

3.  From Greek words  Homeo= same  Stasis= to stand or stay  Term proposed by American Physiologist Walter B Cannon, 1933

4.  Sensing and responding to changes in surrounding environment  Control exchange of materials between cell and its surrounding environment  Obtain nutrients and oxygen from surrounding environment  Eliminate carbon dioxide and other wastes to surrounding environment  Perform chemical reactions that provide energy for the cell  Synthesize needed cellular components

6. 1. DYNAMIC EQUILIBRIUM 2. MULTIPLE STIMULI 3. MAINTAINED BY NEGATIVE FEEDBACK

7.  Homeostasis involves dynamic mechanisms that detect and respond to deviations in physiological variables from their “set point” values by initiating effector responses that restore the variables to the optimal physiological range.

8.  Nervous system  Controls and coordinates bodily activities that require rapid responses  Detects and initiates reactions to changes in external environment  Endocrine system  Secreting glands of endocrine regulate activities that require duration rather than speed  Controls concentration of nutrients and, by adjusting kidney function, controls internal environment’s volume and electrolyte composition

9.  Concentration of oxygen and carbon dioxide  pH of the internal environment  Concentration of nutrients and waste products  Concentration of salt and other electrolytes  Volume and pressure of extracellular fluid

10.  Homeostasis is continually being disrupted by  External stimuli heat, cold, lack of oxygen, pathogens, toxins  Internal stimuli Body temperature Blood pressure Concentration of water, glucose, salts, oxygen, etc. Physical and psychological distresses  Disruptions can be mild to severe  If homeostasis is not maintained, pathological condition even death may result

12.  In order to maintain homeostasis, control system must be able to  Detect deviations from normal in the internal environment that need to be held within narrow limits  Integrate this information with other relevant information  Make appropriate adjustments in order to restore factor to its desired value

13.  The organs and tissues which maintain homeostasis are called control systems.  Autoregulation (local control)  when cells, tissues, organs or systems automatically change in response to signals within themselves.  Intrinsic control  controls that generate a response to change that built into the organ.  Extrinsic control  changes stimulated by signals from outside of the cell, organ, or system  Mediated by Nervous system: brain & spinal cord signals cause change; response is rapid but short term. Endocrine system glands produce hormones that cause changes; response is slower, but lasts longer

14.  Feedforward - term used for responses made in anticipation of a change  Feedback - refers to responses made after change has been detected  Types of feedback systems Negative Positive

15.  Stimulus:  The change from ideal or resting conditions.  Receptor:  The cells or tissue which detects the change due to the stimulus  Relay:  The transmission of the message, via nerves or hormones or both, to the effector.  Effector:  The cells or tissue, usually a gland or muscles, which cause the response to happen.  Response:  An action, at cell, tissue or whole organism level which would not have occurred in the absence of the stimulus  Feedback:  The consequence of the response on the stimulus.  May be positive or negative.

17. A REGULATORY MECHANISM IN WHICH A CHANGE IN A CONTROLLED VARIABLE TRIGGERS A RESPONSE THAT OPPOSES THE CHANGE.

18.  Most common homeostatic feedback mechanism  responses that resists any change from normal range.  Restoration of homeostasis because  Negative feedback causes action that a value is falling too low.  Negative feedback causes action that a value is rising too high.  Values fluctuate within Set limits,  Values change from hour to hour, sometimes with regular diurnal cycles ( circadian rhythms).  Elevated or reduced changes are corrected before they become too extreme.  Can continue forever  Maintains homeostasis

19.  EXAMPLE: body temperature - Set point = 37 C, 98.6 F  Normal limits 36.5- 37.5 C, 97.7-99.5 F Examples:.Body Temperature – Nervous System.Blood Calcium Levels – Endocrine System When blood calcium level drops, parathyroid glands sense that and secrete hormones that cause release of calcium stores from bone. Blood calcium levels return to normal, secretion stops.

20.  Baroreceptors in walls of blood vessels detect an increase in BP  Brain receives input and signals blood vessels and heart  Blood vessels dilate, HR decreases  BP decreases

21. A REGULATORY MECHANISM IN WHICH THE RESPONSE TO A STIMULUS, IN A CONTROL SYSTEM, CAUSES THE CONTROLLED VARIABLE TO MOVE FARTHER FROM THE SET POINT.

22.  Rare homeostatic feedback mechanism  The response enhances the original  stimulus  Positive feedback promotes changes that are developing, so they become more extreme  Positive feedback causes action that a value is falling causing it to fall farther.  Positive feedback causes action that a value is rising causing it to rise higher.  Positive feedback in disease - ex. Hypothalamus increases set point. Development of a fever. Examples:.Hemorrhage.Childbirth.Lactation

23.  Unstable system  It is used to trigger a sudden event or phenomenon  Can not continue forever, always has a limit  Does not result in homeostasis  Beneficial only in special circumstances  Example in childbirth, stretching of uterus elicits production of hormones that stimulate contraction of uterine muscles; this leads to more stretching of uterus, more hormone secretion, more muscle contractions; loop is broken upon birth of a baby

24.  Stretch receptors in walls of uterus send signals to the brain  Brain induces release of hormone (oxytocin) into bloodstream  Uterine smooth muscle contracts more forcefully  More stretch, more hormone, more contraction etc.  Cycle ends with birth of the baby & decrease in stretch