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 O2 and CO2
• 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 is 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
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

22. THANK
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