1. Coordination & Regulation

2. Environments
A multicellular organism requires a relatively stable internal environment.

3. Word Work!
Stable Not likely to move or change. Synonym: constant

4. Word Work!
Chemical compounds which are not stable can be very dangerous.

5. Cellular Environments
Extracellular (intercellular) fluid surrounds our cells (eg. tissue fluid and blood plasma).
Intracellular fluids are the fluids within the cell (eg. Cytosol)

6. Pause and Think
What is it that separates extracellular fluids from intracellular fluids?

7. Homeostasis
Homeostasis is the maintenance of a relatively stable internal environment despite large swings in the external environment.
Homeostasis = same state

8. A Balancing Act!

9. Body systems & Homeostasis
ALL body systems (except the reproductive system) play a part in maintaining homeostasis. When a CHANGE is found, body systems REACT to bring back the balance.

10. Regulation
Regulation is the reaction to fluctuations around a set-point.
i.e. Variables are kept within narrow limits!
e.g. Core body temperature is kept within a narrow range from about 36–39 °C

11. Tight Regulation

12. Variables Some of the major variables:
Temperature (Temperature regulation)
Blood glucose (Blood glucose regulation)
Water (Osmoregulation)
Blood pressure (Blood pressure regulation)
Ion concentration
Blood pH
Urea in plasma

14. Stimuli
Cells must respond to a change in the internal or external environment (stimulus).

15. Monitor and Correct Homeostasis involves:
Monitoring levels of variables, and
Correcting changes in these levels. typically by negative feedback.

16. Monitor and Correct
Monitoring the conditions in the body
Receptors detecting a change (in a variable) from a stable state.
- Thermoreceptors
- Photoreceptors
- Chemoreceptors
Effectors are cells of various body systems reacting to restore the balance (action)

17. Stimulus-Response Model
SR CERN
A stimulus is detected by a receptor.
If the intensity of the stimulus is sufficient, messages are transferred to a control centre.
Messages are then passed to effectors, which produce a response.

18. Summary of Key Elements
Stimulus: A disturbance which starts the loop.
Receptor: detects the stimulus, is activated and sends a signal to the control centre.
Control Centre: The signal is received and compares this to the set-point.
Effector: The endocrine or nervous system responding.
Response: The action resulting from the effector.

19. Negative Feedback
System of control in which change in a variable is detected, for example a decrease, and action occurs to produce a change in the opposite direction, for example an increase.
The response COUNTERACTS the initial stimulus (change)

20. The principle of negative feedback

21. Negative Feedback Systems
The nervous and endocrine (hormonal) system do NOT work independently of each other. Instead, they interact with each other in coordinating the activities of the body.

22. A COMPARISON
The nervous system provides rapid responses to produce efficient coordinated movements. The endocrine system is generally a slower system, although some responses are still very quick.

23. Homeostasis in the Human Body
Maintenance of Blood Glucose Levels

24. Activity 1. 2. 6. 3. 4. 5.

25. Failure of Homeostasis
Factors that may affect restoration to ‘normal’ state:
Infection
Trauma
Exposure to toxic substances
Extreme conditions
Autoimmune diseases
Inherited disorders