Homeostasis

Homeostasis, mileu interior, constantly internal environmental, positive feedback, negative feedback, adaptation

1. HOMEOSTASIS BY: GROUP 7 (Roll No.76-88)

2. HOMEOSTASIS The term coined by American physiologist Walter Cannon homeo = same ; statis = standing Maintenance of a Nearly Constant Internal Environment Maintenance of a Nearly Constant Internal Environment

3. WHAT IF THERE IS CHANGE IN OUR INTERNAL ENVIRONMENT ? Depending upon the degree of change; Discomfort Disease Damage Death So any significant change in the environment is harmful to an organism. When the fish is sick Change the water

4. Extracellular Fluid – The “ Internal Environment ” In the ECF, there are the ions and nutrients needed by the cells to maintain life. Thus, all cells live in essentially the same environment – the ECF. Claude Bernard – The Father of Physiology introduced the term ‘milieu interieur ’ for the internal environment.

5. HOMEOSTATIC MECHANISMS The various physiological processes which serve to restore the normal state , once it has been disturbed. They maintain constant: Concentration of Oxygen and Carbon dioxide Concentration of nutrients and waste products Concentration of salts and other electrolytes Volume and pressure of ECF

6. ALL ORGANS AND ORGAN SYSTEMS OF BODY HELP IN MAINTENANCE OF HOMEOSTASIS Cardiovascular System Respiratory System Nervous System Endocrine System GI System Excretory System Skeletal System Integumentary System Reproductive System

7. FEEDBACK MECHANISMS A feedback mechanism is a cycle in which some proportion of output signal is “ fed back” to the input in order to control behaviour of some 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

8. COMPONENTS OF A FEEDBACK SYSTEM SENSOR (RECEPTOR) : Detects specific changes (stimuli) in the environment. INTEGRATOR : Act to direct impulses to the place where a response can be made EFFECTOR : Performs the appropriate responses. FEEDBACK LOOP

9. NEGATIVE FEEDBACK Mechanisms that maintain the factor at some mean value. Reverse a change. Restore abnormal values to normal.

10. NEGATIVE FEEDBACK LOOP

11. EXAMPLE: BLOOD PRESSURE HORMONE REGULATION (Growth Hormone Regulation)

12. POSITIVE FEEDBACK Strengthens or reinforces a change. Makes abnormal values more abnormal. Produces ‘Vicious Cycle’. But in the 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.

13. POSITIVE FEEDBACK LOOP

14. EXAMPLES: ACTION POTENTIAL BLOOD CLOTTING PARTURITION LACTATION LH SURGE

15. NEGATIVE vs POSITIVE FEEDBACK

16. EFFECTIVENESS OF FEEDBACK CONTROL- THE PRINCIPLE OF GAIN

17. APPLIED PHYSIOLOGY

18. TYPE 1 DIABETES MELLITUS Blood Glucose Homeostat ceases to function. Beta cells of the pancreatic islets are destroyed. Glucose sensor is absent and thus the Insulin level in the blood remains at zero. Results in gluconeogenesis by the liver. Fatal if not treated.

19. HYPERPARATHYROIDISM Plasma ionised Calcium homeostat ceases to function. Over production of parathyroid hormone ( Collipse Hormone). Leads to spontaneous fractures . Conformational changes in many cell surface proteins (Ion channels and hormone or Neurotransmitter receptors) Lethargy, muscle weakness, anorexia, constipation and labile emotions.

20. HYPERNATREMIA – HIGH LEVELS OF SODIUM IONS IN THE BLOOD ADH homeostat ceases to function. Body water homeostat is compromised. Daily water losses via exhaled air, feces and insensible sweating. Zero blood ADH signal. Kidneys produce huge unchanging volumes of very dilute urine, causing dehydration and death if not treated.

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