1. Homeostasis
Chapter 1

2. Learner Outcome:
To discover and describe homeostatic regulation in the human body and predict the consequences of the failure to maintain homeostasis.

3. Defined
Homeostasis is the relative constancy of the body’s internal environment.
External (environmental) conditions may change drastically.
Dynamic Equalibrium
If internal conditions change to a large degree – the result is illness.

4. Terminology
Normal Range – a range of values for a variable that allow for normal function of the body and its tissues.
Set Point – the ideal value of a variable.
Sensor – the part of the body that detects an internal environmental change and signals the regulatory center.
Effector – the part of the body that receives the information from the regulatory center and reverses or amplifies the change.
Regulatory Center – part of the body that recognizes values outside of the normal range and activates the effector.

5. Negative Feedback
Homeostatic mechanism that keeps a variable close to a particular value or set point.

6. Fig. 1.7a
Negative Feedback

7. Fig. 1.7b
Mechanical Example

8. Fig. 1.8

9. Positive Feedback
Homeostatic mechanism that brings about an even greater deviation from the set point.
EX: Birth process
Baby  Cervix  stimulates secretion of oxytocin from pituitary  causes uterine contractions  etc.

10. Disease
The result of homeostatic failure and the malfunctioning of the structure due to that failure.
Local diseases are located in a specific area of the body whereas systemic diseases affect the entire body.
Acute diseases occur suddenly and usually last a short time whereas chronic disease tend to be severe and long term.