1. Homeostasis
August 11,

2. Homeostasis The maintenance of relatively stable internal conditions
Dynamic process – the body is constantly regulating to keep conditions within acceptable ranges

3. Examples of Homeostasis
What are some variables maintained by homeostasis?

4. Examples of Homeostasis
Many variables are maintained by homeostasis.
Examples include:
Temperature
Blood pH
Blood sugar
Water balance
Blood pressure
Ion balance

5. Homeostatic Control Mechanisms

6. Homeostatic Control Mechanisms
Analogies
Thermostat
Cruise control
others?

8. What is the ...
Variable?
Stimulus?
Receptor?
Control center?
Effector?

9. What is the ...
Variable?
Stimulus?
Receptor?
Control center?
Effector?
Receptors aren’t shown on this picture, but there are two sets of thermoreceptors: some in the hypothalamus to measure internal temperature , and some in the skin to measure external temperature

10. You do: What is the ...
Variable? Stimulus? Receptor? Control center? Effector?

11. Receptors aren’t shown again, but there are two types of calcium receptors scattered throughout the body
You do: What is the ...
Variable? Stimulus? Receptor? Control center? Effector?

12. Negative Feedback Mechanisms
Most homeostatic mechanisms are examples of negative feedback. In negative feedback, the output acts to change the direction of the stimulus. Example: If the body is hot, the hypothalamus will activate the sweat glands and dilate the blood vessels (the two outputs) … both of which will act to reduce the body temperature.

13. Positive Feedback Mechanisms
Some processes in the body are positive feedback mechanisms. In positive feedback, the output enhances the stimulus

14. Positive or Negative Feedback?
Blood Clotting
Blood Pressure

15. Positive or Negative Feedback?
Blood Clotting
Blood Pressure
Positive –
The output (platelet adhering) increases the original stimulus (platelet-attracting chemical)
Negative–
The output (decreased heart rate / increased diameter) decreases the original stimulus (high blood pressure)

16. Positive and Negative Feedback
In pairs, write a Venn diagram comparing and contrasting positive and negative feedback. Also, identify other examples of positive and negative feedback and be prepared to justify why they are examples. ** may be in or out of the body** (5 minutes)

17. Homeostatic Imbalance
Most disease is caused by a disturbance of homeostatic mechanisms known as homeostatic imbalance.
Homeostatic imbalance can result from
Aging
Genetic mutations
Pathogens
Environmental factors

18. Congo Line review
- 10 minutes -

19. Homework
Quiz next class!

20. What were our objectives today and what did you learn?
Closure
What were our objectives today and what did you learn?

21. Exit Ticket Study this diagram. What is the stimulus?
What are the effectors?
Is this + or – feedback, and how can you tell?

22. Exit Ticket Identify the body system to which each organ belongs
Pancreas
Liver
Ex) Which system cleans and returns body fluids to the blood stream?