1. HOMEOSTASIS AND FEEDBACK CONTROL pp 1041-1042

2. HOMEOSTASIS REVIEW
Homeostasis: maintaining stable internal environment
Bringing body back to normal

3. FEEDBACK MECHANISMS
Process that uses the conditions of one component to regulate the function of the other
Part of a chain of cause-and-effect that forms a circuit or loop

5. Four Parts to A Feedback Loop
Stimulus: A change to the baseline condition (set point)
Receptor: an organ or structure that monitors a specific condition
Control Center: An organ that process the change or information from the receptor and determines next action.
Effector: Receives directions from the control center and produces a response that changes condition.

6. POSITIVE FEEDBACK
The product stimulates production (amplify) of the initial stimulating substance or action until the stimulus or change is gone (i.e. contractions during labor)

7. Negative feedback: the product (response) stops production of the initial stimulus to bring back to normal
NEGATIVE FEEDBACK

8. At the Molecule Level
In a series of enzyme mediated reactions, the last product (molecule) made will inhibit the activity of the first enzyme

9. At the Organ System Level
Many organs, chemical signals, and tissues work together to slow or stop the initial stimulus or change to the body
QUESTION: What does your body do when you are hot? When you are cold?

11. Integumentary system
The subcutaneous layer (fat cells) and body hair provide insulation against heat loss
The dermis (inner layer) contains blood vessels, nerves, hair follicles, oil glands, and sweat glands (for cooling)
Melanocytes in the epidermis produce melanin for protection from the sun

13. Muscular system
Shivering is the uncontrollable activity of muscles contracting
When the myosin “heads” walk along the actin ATP is required to walk and to release along the action
Using ATP generates heat

14. Figure 40.8 A nonliving example of temperature regulation: control of room temperature.14

15. NEGATIVE FEEDBACK cont
Most of the systems use negative feedback to bring the body back to the set point
Negative feedback consists of two loops to form a “figure 8”. This addresses both extremes away from a set point (ie. Thermoregulation, urine production)
NEGATIVE FEEDBACK cont