Biology 30 Unit 1
Homeostasis & The
Nervous System
Homeostasis:
Defined
• Homeostasis
– maintaining a constant internal environment.
• Temp.
= 37ºC
• pH
= 7.4
• [Blood glucose] = 0.1%
Homeostasis:
•
Homeostatic mechanisms
– processes and activities that help to
maintain homeostasis
– three functional components
1. Receptor: detects change
2. Control center: process info and sends
instructions for response
3. Effector: carries out response
Homeostatic mechanisms
•
Homeostasis is achieved through
feedback regulation
•
There are two types of feedback systems
1. Positive Feedback (non-homeostatic)
2. Negative Feedback (homeostatic)
Feedback Regulation
• Positive Feedback
– 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
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
Thermostat/Furnace
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.
Maintenance of a Constant
Temperature 37o
• Decrease body temp: • Increase Body temp:
–
–
–
–
–
Vasodilatation
Sweat
Breathing
Decrease metabolism
Behavioral changes
• Clothing
• Basking
–
–
–
–
Vasoconstriction
Increase metabolism
Insulation (fat layer)
Increase Muscle activity
• Shivering
• Goose flesh
– Behavioral changes
• Clothing
• Huddling
Maintenance of a Constant
Temperature 37o
Vasodilation
Vasoconstriction
Maintenance of a Constant
Temperature 37o