Homeostasis & Control Mechanisms of The Body

Homeostasis is the state of steady internal, physical, and chemical conditions maintained by living systems.

1. Homeostasis & Control Mechanisms of The Body “MohmmadRjab” S. Seder

2. Homeostasis Homeostasis is the state of steady internal, physical, and chemical conditions maintained by living systems. Maintenance of nearly constant conditions in the internal environment. The various physiologic arrangments which serve to restore the normal state once it has been distributed.

3. What needs to be mainteined constant in the internal environment? Concentration of O 2 and CO 2 pH of the internal environment Concentration of nutrients and waste products Concentration of salts and other electrolytes Volume and pressure of blood vessels

4. 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

5. How homeostatic control mechanisms work? Homeostatic control mechanisms work through ”Feedback Mechanisms” Status of a body condition is continually monitored, evaluated, changed, remonitored & reevaluated.

6. Feedback Mechanisms A feedback mechanism may operate at: Tissue level Organ level Organ system level Body level, integrating with other organ systems Feedback mechanisms can be: Positive Feedback Negative Feedback (more common)

7. A feedback system consists of three components Stimulus: A stimulus is something that disrupts the body’s homeostasis 1- SENSOR (RECEPTOR): detects specific changes (stimuli) in the environment. 2- INTEGRATOR (CONTROL CENTER): act to direct impulses to the place where a response can be made. 3- EFFECTOR: performs the appropriate response.

8. A Feedback Loop

9. Negative Feedback Mechanism Is a type of regulation in biological systems in which the end product of a process in turn reduces the stimulus of that same process. Mechanisms that maintain the factor at some mean value. Reverse a change. Restore abnormal values to normal.

10. Negative Feedback Mechanism

11. Negative Feedback Loop

12. Biological Negative Feedback in Body Temperature Blood Pressure Metabolism Regulation of Blood Suagr Production of RBCs

13. Example: Negative Feedback Blood Pressure Regulation

14. Example: Negative Feedback Body Tempereture Regulation

15. Positive Feedback Mechanism Positive feedback is a process in which the end products of an action cause more of that action to occur in a feedback loop. Strengthens and reinforces a change. Makes abnormal values more abnormal. Produces “Vicious Cycle” . A vicious cycle i s a negative series of events that build on and reinforce each other. If you can't you can't get a job without experience, but you can't get experience without a job, then you are in a vicious cycle.

16. Positive Feedback Loop

17. Positive Feedbacks in Body Action potential Clotting of blood Parturition Release of calcium from SR Sexual arousal LH surge

18. Example: Positive Feedback Membrane Depolarization

19. Example: Positive Feedback Childbirth A positive feedback loop comes into play during childbirth. In childbirth, the baby's head presses on the cervix—the bottom of the uterus, through which the baby must emerge—and activates neurons to the brain. The neurons send a signal that leads to release of the hormone oxytocin from the pituitary gland. Oxytocin increases uterine contractions, and thus pressure on the cervix. This causes the release of even more oxytocin and produces even stronger contractions. This positive feedback loop continues until the baby is born.

20. Negative Vs Positive Feedback

21. Effectiveness of a feedback control; the principle of GAIN GAIN = Correction/Error Higher the gain, more efficient is the system Example: 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

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