1. Homeostasis What is homeostasis?
What do we call the body when it is not in homeostasis?
What is a model for homeostasis? What is a stimulus? What is the afferent and efferent pathway?
What is a positive feedback loop?
What is a negative feedback loop?
What are examples of positive and negative feedback loops in the body?

2. Necessary Life Functions
Maintain boundaries
Movement
Locomotion
Movement of substances
Responsiveness
Ability to sense changes and react
Digestion
Break-down and absorption of nutrients

3. Necessary Life Functions
Metabolism—chemical reactions within the body
Produces energy
Makes body structures
Excretion
Eliminates waste from metabolic reactions
Reproduction
Produces future generation
Growth
Increases cell size and number of cells

4. Homeostasis is a coordinated effort to maintain balance!
Figure 1.3

5. Homeostasis Homeostasis—maintenance of a stable internal environment
A dynamic state of equilibrium
Homeostasis is necessary for normal body functioning and to sustain life
Homeostatic imbalance
A disturbance in homeostasis resulting in disease

6. Variable (in homeostasis)
Input: Information sent along afferent pathway to
Control center
Output: Information sent along efferent pathway to activate
Receptor (sensor)
Effector
Change detected by receptor
Response of effector feeds back to influence magnitude of stimulus and returns variable to homeostasis
Stimulus: Produces change in variable
Imbalance
Variable (in homeostasis)
Imbalance
Figure 1.4

7. Variable (in homeostasis)
Figure 1.4, step 1a

8. Variable (in homeostasis)
Stimulus: Produces change in variable
Imbalance
Variable (in homeostasis)
Imbalance
Figure 1.4, step 1b

9. Variable (in homeostasis)
Receptor (sensor)
Change detected by receptor
Stimulus: Produces change in variable
Imbalance
Variable (in homeostasis)
Imbalance
Figure 1.4, step 2

10. Variable (in homeostasis)
Input: Information sent along afferent pathway to
Control center
Receptor (sensor)
Change detected by receptor
Stimulus: Produces change in variable
Imbalance
Variable (in homeostasis)
Imbalance
Figure 1.4, step 3

11. Variable (in homeostasis)
Input: Information sent along afferent pathway to
Control center
Output: Information sent along efferent pathway to activate
Receptor (sensor)
Effector
Change detected by receptor
Stimulus: Produces change in variable
Imbalance
Variable (in homeostasis)
Imbalance
Figure 1.4, step 4

12. Variable (in homeostasis)
Input: Information sent along afferent pathway to
Control center
Output: Information sent along efferent pathway to activate
Receptor (sensor)
Effector
Change detected by receptor
Response of effector feeds back to influence magnitude of stimulus and returns variable to homeostasis
Stimulus: Produces change in variable
Imbalance
Variable (in homeostasis)
Imbalance
Figure 1.4, step 5

13. Maintaining Homeostasis
The body communicates through neural and hormonal control systems
Receptor
Responds to changes in the environment (stimuli)
Sends information to control center

14. Maintaining Homeostasis
Control center
Determines set point
Analyzes information
Determines appropriate response
Effector
Provides a means for response to the stimulus

15. Feedback Mechanisms Negative feedback
Includes most homeostatic control mechanisms
Shuts off the original stimulus, or reduces its intensity
Works like a household thermostat

16. Feedback Mechanisms Positive feedback
Increases the original stimulus to push the variable farther
In the body this only occurs in blood clotting and during the birth of a baby