1. Homeostasis & The Nervous System
Biology 30 Unit 1
Homeostasis & The Nervous System

2. Homeostasis: Defined Homeostasis
maintaining a constant internal environment.
Temp = 37ºC
pH = 7.4
[Blood glucose] = 0.1%

3. Homeostasis: Homeostatic mechanisms
processes and activities that help to maintain homeostasis
three functional components
Receptor: detects change
Control center: process info and sends instructions for response
Effector: carries out response

4. Homeostatic mechanisms
Homeostasis is achieved through feedback regulation
There are two types of feedback systems
Positive Feedback (non-homeostatic)
Negative Feedback (homeostatic)

5. Feedback Regulation Positive Feedback Examples
Feedback that increases the initial fluctuation
Examples
Microphone picking up a sound then amplifying that sound and picking it up again...
Contractions during childbirth
Fever

6. Feedback Regulation Negative Feedback
Feedback that counteracts the initial fluctuation
tends to stabilize a system, correcting deviations from the setpoint
Examples
The action of heat on a thermostat
Thermoregulation
Blood glucose levels pH

7. Thermostat/Furnace

8. Thermoregulation
The expenditure of energy involves elaborate chemical reactions, most of which are sensitive to temperature.
In mammals the metabolic cost of maintaining endothermy is expensive, requiring at least 90% of total metabolism to be devoted to the regulation of body temperature.

9. Maintenance of a Constant Temperature 37o
Decrease body temp:
Vasodilatation
Sweat
Breathing
Decrease metabolism
Behavioral changes
Clothing
Basking
Increase Body temp:
Vasoconstriction
Increase metabolism
Insulation (fat layer)
Increase Muscle activity
Shivering
Goose flesh
Behavioral changes
Clothing
Huddling

10. Maintenance of a Constant Temperature 37o
Vasodilation
Vasoconstriction

11. Maintenance of a Constant Temperature 37o