Homeostasis refers to the body's ability to regulate its internal environment to maintain a stable and constant condition. It involves various mechanisms to regulate key variables such as temperature, fluid balance, and pH levels. Homeostatic control systems use negative feedback loops to detect changes and counteract them to return conditions back to normal. Positive feedback mechanisms can also be involved to accelerate necessary responses like clotting, but these are tightly regulated to avoid harm. Multiple organ systems work in coordination through neural and hormonal signaling to maintain homeostasis.

1. HOMEOSTASIS

2. Introduction
• Definition:
– Homeostasis means condition in which internal
environment of body remains relatively constant despite
changes in external environment
– For this purpose, living membrane with varying
permeabilities such as vascular endothelium & cell
membrane play important role in exchange of fluid,
electrolyte, nutrient & metabolites across compartment of
body fluid
• Examples of Homeostatic mechanism:
– Kidney : Ion concentration
– Lungs : Removal of acid forming CO2
– GIT : Nutrients

3. Internal environment (IE)
Cells – are capable of living, growing, & performing
their special functions
• So, long as proper concentration of O2, Glucose,
different ion, AA, fatty substance & other
constituent available in IE
ECF – since all body cells essentially depend upon
ECF for maintenance of cellular life

4. Examples of IE changes
1. Carbohydrate rich diet : disturb blood sugar
level
2. Heavy sweating : decreases Na+ conc. of ECF
3. Violent exercise / expose to heat : elevates ECF
temperature
(Homeostasis is maintenance of IE (ECF) at a
constant)

5. The factors involved in maintenance of IE
(Homeostasis)
• Maintenance of pH of ECF (acid–base balance)
• Regulation of temperature
• Maintenance of water and electrolyte balance
• Supply of nutrients, oxygen, enzymes & hormones
• Removal of metabolic and other waste products,

6. System involved in Homeostasis
• Resp. system : PH & temperature
• GIT : Nutrients
• Liver : Modifying & storage
• Musculoskeletal : Movements & protection from
adverse environments.
• CNS : Control & interpretation.
• ANS : Vegetative functions
• CVS : Compensatory adjustment ( eg. fainting)
• Endocrine : Neuro-endocrine activity.
• Immune system : Interleukins & cytokines
• Kidney : Acid base balance

7. Components of Homeostasis control system

8. Homeostasis Using a Neural Pathway

9. Mechanism of regulation
• Control loops (sensory inputs )
– Open loop
– Closed loop
• Intrinsic
–Automatic response, involve one
organ/tissue/cell.
• Extrinsic
–Controlled by nervous & endocrine system.
–Feedback mechanism also included

10. Example- Intrinsic Mechanism

11. Example- Extrinsic Mechanism
Neural Hormonal

12. Mechanism of action of Homeostatic control
systems
• By ‘feedback’ mechanism (2 Types)
– Negative feedback mechanism
– Positive feedback mechanism
• Other control system
- feed-forward control
- Adaptive control system

13. Negative feedback mechanism
• Most control systems of body act by negative
feedback.
• If activity of a particular system is increased or
decreased, a control system initiates a negative
feedback, which return activity toward normal
Features :-
• Change in variable being regulated brings about
responses that tend to push variable in direction
opposite to original change
• Opposite effect is mainly ‘inhibitory’.
• This minimizes changes from set point of system
leading to stability.

14. Cont…Negative feedback Mechanism

15. Examples of negative feedback Mechanism

Cortisol by suprarenal glands

Blood cortisol concentration
Pituitary and Hypothalamus
ACTH output
Stimulation of suprarenal gland
Cortisol output
1. Cortisol

16. Cont…
2. Thyroxine secretion

17. Cont…
3. Maintenance of water balance

18. Cont…
4. Regulation of blood glucose

19. Other example of Negative feedback
mechanism
5. When BP suddenly rises or lowers, it initiates a
series of reactions that tries to bring blood
pressure to normal levels
6. Regulation of body temperature

20. Positive feedback mechanism
• Positive feedback is better known as a vicious circle
• Usually it is harmful & in some instances even
death can occur due to positive feedback…For e.g.
(Flowchart showing how +ve feedback mechanism can cause death)

21. Cont…
• A mild degree of feedback can be overcome by
negative feedback control mechanisms of body,
& vicious cycle fails to develop
For example
• when a patient bleeds 1 L of blood instead of 2 L,
-ve feedback mechanisms of controlling BP may
overcome +ve feedback, & BP will return to
normal
• So, Homeostatic systems utilizing +ve feedback
have two primary characteristics:-
- Time limitation
- Intensification

22. Cont…Positive feedback mechanism

23. Further, sometimes +ve feedback can serve useful
purposes
Examples of Positive feedback Mechanism
1. Clot formation followed by rupture of vessels is
accelerated by vicious cycle of thrombin formation
so stops bleeding.
2. Child birth during labour is facilitated by
progressively increasing uterine contractions due to
positive feedback from stretching of cervix by head
of baby
3. Generation of nerve signals by vicious cycle of
progressive leakage of Na+ ions from channels set
up following stimulation of membrane of nerve fibre
is due to +ve feedback

24. 1. Clot formation

25. 2. Child birth during labour

26. 3. Generation of nerve signals
Memb. of nerve fiber (stimulated)
Opening of Na++ channel
Changes memb. Potential
Opening of more Na++ channel
Nerve action potential generated
Process continues.

27. Harmful Effects of Positive Feedback
• Positive feedback can be harmful. Examples of these
harmful outcomes:
– Fever causes +ve feedback within homeostasis that
increases body temperature continually. If the
temperature > 45 degrees C (113 degrees F) cellular
proteins denature, metabolism stops & death.
– Chronic hypertension favors process of
atherosclerosis which causes narrowing of blood
vessel openings. Resulting in more damage to walls
of blood vessels.

28. Other control system
Feed forward:-
• A direct effect of stimulus on control system
before the action of feed back signals.
• Frequently used along with negative feedback
• Anticipate changes in the variable improves speed
of body’s homeostasis responses minimizes
fluctuations in level of variable

29. Cont…..

30. Adaptive control system
• Adaptive control system refers to a delayed type
of negative feedback mechanism
• This is seen in nervous system

31. For example---
• when some movements of body occur very rapidly, there is
not enough time for signal travel from peripheral parts of
body to brain & then back to periphery again to control
movements.
• Under such circumstances brain uses a principle called
feed-forward control to cause required muscle contraction
which retrospectively is conveyed to brain by sensory
nerve signals from moving part.
• If the movement performed is found incorrect, then brain
corrects the feed-forward signals that it sends to muscle
next time movement is required.
• Such a correction made by successive retrospective
feedback mechanism is called adaptive control.
Cont……

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