1. Homeostasis

2. Homeostasis
Homeostasis is the maintenance of a stable internal environment.

3. Homeostasis
Homeostasis represents a state of DYNAMIC EQUILIBRIUM.

4. Homeostasis
Homeostasis represents a state of DYNAMIC EQUILIBRIUM. This means that adjustments are always being made to keep the variables within an acceptable range.

5. Homeostasis

6. Homeostasis
All homeostatic mechanisms involve three components:

7. Homeostasis All homeostatic mechanisms involve three components:
Receptors (sensors)
Monitors the environment & responds to a stimulus

8. Homeostasis All homeostatic mechanisms involve three components:
Receptors (sensors)
Monitors the environment & responds to a stimulus
Transmits the stimulus (information) to a control center along a afferent pathway

9. Homeostasis All homeostatic mechanisms involve three components:
Control Center
Determines the “set points” or range to be maintained

10. Homeostasis All homeostatic mechanisms involve three components:
Control Center
Determines the “set points” or range to be maintained
Establishes the type of response

11. Homeostasis All homeostatic mechanisms involve three components:
Control Center
Determines the “set points” or range to be maintained
Establishes the type of response
Sends this information though a Efferent Pathway

12. Homeostasis All homeostatic mechanisms involve three components:
Effector
Mechanism for controlling the variable or response

13. Homeostasis All homeostatic mechanisms involve three components:
Effector
Mechanism for controlling the variable or response
A reduced response is called a NEGATIVE FEEDBACK

14. Homeostasis All homeostatic mechanisms involve three components:
Effector
Mechanism for controlling the variable or response
A reduced response is called a NEGATIVE FEEDBACK
An increase in response is a POSITIVE FEEDBACK

15. Information sent along efferent pathway to effector.
Figure 1.4 Interaction among the elements of a homeostatic control system.
Output:
Information sent along
efferent pathway to
effector. 4
Input: Information
sent along afferent
pathway to control
center. 3
Control
Center
Afferent
pathway
Efferent
pathway 2
Receptor
Effector 5
Receptor
detects
change.
Response
of effector
feeds back
to reduce
the effect of
stimulus
and returns
variable to
homeostatic
level. 1
Stimulus
produces
change in
variable.
BALANCE

16. Homeostasis
Negative Feed Back is the major mechanism for controlling homeostatic responses.

17. Homeostasis
Negative Feed Back is the major mechanism for controlling homeostatic responses.
The stimulus is either turned off or reduced in its intensity

18. Homeostasis Consider body temperature:
Temperature change in the body is the variable

19. Homeostasis Consider body temperature:
Temperature change in the body is the variable
The change in temperature up or down is the response
Can you think of any other examples?

20. Temperature-sensitive Temperature-sensitive
Figure 1.5 Regulation of body temperature by a negative feedback mechanism.
Control Center
(thermoregulatory
center in brain)
Information sent
along the afferent
pathway to control
center
Information sent
along the efferent
pathway to
effectors
Afferent
pathway
Efferent
pathway
Receptors
Temperature-sensitive
cells in skin and brain
Effectors
Sweat glands
Sweat glands activated
Response
Evaporation of sweat
Body temperature falls;
stimulus ends
Stimulus
Body temperature
rises
BALANCE
Stimulus
Body temperature falls
Response
Body temperature rises;
stimulus ends
Receptors
Temperature-sensitive
cells in skin and brain
Effectors
Skeletal muscles
Efferent
pathway
Afferent
pathway
Shivering
begins
Information sent
along the efferent
pathway to effectors
Information sent
along the afferent
pathway to control
center
Control Center
(thermoregulatory
center in brain)

21. Can you think of any examples?
Homeostasis
Positive Feed Back is a minor mechanism for controlling homeostatic responses and is used for only occasional events.
The stimulus goes in the same direction as the response. One increases the other increases.
Can you think of any examples?

22. Homeostasis
Blood Clotting and Labor Contractions

23. Homeostasis

24. 1 occurs in blood vessel wall. Positive feedback cycle is initiated. 3
Figure 1.6 Summary of the positive feedback mechanism regulating formation of a platelet plug.
Break or tear
occurs in blood
vessel wall. 1
Positive feedback
cycle is initiated. 3
Released
chemicals
attract more
platelets. 2
Platelets
adhere to site
and release
chemicals.
Positive
feedback
loop
Feedback cycle ends
when plug is formed.
Platelet plug
forms. 4

25. Homeostasis
Disease occurs when the homeostatic mechanisms fail or are overwhelmed.
Examples include:
Heart Failure
Anaphylaxis
Diabetes
Hemophilia

26. Congested Heart Failure

27. Anaphylaxis

28. Anaphylaxis

29. Anaphylaxis

30. Diabetes

31. Homeostasis
How about a cold or flu? How about cancer?