1. homeostasis
Prepared By
Dr. Sisara Bandara Gunaherath
(MBBS)

2. Definition of Homeostasis
homeo = same; stasis = standing
Homeostasis is the term we use to describe the constant state of the internal environment.
Homeostasis is a state of balance in the body.
The processes and activities that help to maintain homeostasis are referred to as homeostatic mechanisms.

3. Examples of Homeostasis
Body Temperature
Water Balance
Chemistry Balance of Blood

4. BASIC COMPONENTS OF A FEEDBACK SYSTEM
1. A RECEPTOR :DETECTS
CHANGES (STIMULI) IN THE BODY.
2. A CONTROL CENTER :
DETERMINES A SET POINT FOR A
NORMAL RANGE.
3. AN EFFECTOR : CAUSES THE
RESPONSE DETERMINED BY THE
CONTROL CENTER.

5. A Temperature Control System
To help us understand homeostasis in living organisms, let us first look at a non-living system. We will use a temperature control system for a room which has many similar features to homeostatic mechanisms…. Click on the thermostat.

7. A Review Example: thermostatic heating system in a home
Components of an automatic control system
Variable is the characteristic of the internal environment that is controlled by this mechanism (internal temp in this example).
Sensor (receptor) detects changes in variable and feeds that information back to the integrator (control center) (thermometer in this example).

8. Example Continued
Integrator (control center) integrates (puts together) data from sensor and stored "set point" data (thermostat in this example).
Set point is the "ideal" or "normal" value of the variable that is previously "set" or "stored" in memory.
Effector is the mechanism (furnace in this example) that has an "effect" on the variable (internal temperature in this example).

9. External stimuli Internal stimuli
Homeostasis is continually being challenged 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

10. Homeostatic Control Systems
Feed forward - 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

11. Feedback System A feedback system must have 3 parts:
1. Something to sense the environment—a sensor or the receptor 
2. Analyzes the input, determines the appropriate response – a control center / integrator   
3. A response mechanism that responds to the control center – a effector

13. The 2 types of responses are known as:  
   1. Negative feedback  
    2. Positive feedback 

14. NEGATIVE FEEDBACK A REGULATORY MECHANISM IN
WHICH A CHANGE IN A CONTROLLED
VARIABLE TRIGGERS A RESPONSE
THAT OPPOSES THE CHANGE.

15. NEGATIVE FEEDBACK

16. Negative Feedback Loop
Negative feed back loop consists of:
Receptor - structures that monitor a controlled condition and detect changes
Control center - determines next action
Effector
receives directions from the control center
produces a response that restores the controlled condition

17. NEGATIVE FEEDBACK

18. A REGULATORY MECHANISM IN WHICH THE RESPONSE TO A
POSITIVE FEEDBACK
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.

19. POSITIVE FEEDBACK USUALLY DOES NOT MAINTAIN HOMEOSTASIS.
IT IS CHARACTERIZES BY BEING
SHORT IN DURATION, AND
INFREQUENT.

20. POSITIVE FEEDBACK