1. KEY CONCEPT Homeostasis is the regulation and maintenance of the internal environment.

2. Conditions within the body must remain within a narrow range.
Homeostasis involves keeping the internal environment within set ranges.

3. Control systems help maintain homeostasis like ...
Sensors = gather data
senses
B. Control Center= receives data, interprets info, sends messages out.
 brain
C. Communication System= delivers messages to target organs, tissues
PNS (e.g. motor neurons)
D. Targets = respond to change.
muscles, glands (release hormones)
pore
sweat
glands
hair
follicle
muscle
goose
bump

4. Negative feedback loops are necessary for homeostasis.
Feedback compares current conditions to the body’s comfort levels (=Set Ranges).
Negative feedback counteracts change and brings the body back to homeostasis.
O2 / CO2 level returns to normal
Holding breath, CO2 levels rise,
Negative Feedback Loop
Control system forces exhale, inhale

5. Ex. #2 = Growth hormones stimulate cell division
Positive feedback: increases change away from the set points. Needed for rapid change in the body.
Ex. #1 = Torn blood vessels stimulates the release of clotting factors to stop blood flow.
platelets
fibrin
white blood cell
red blood cell
blood vessel
clot
Ex. #2 = Growth hormones stimulate cell division

6. Thermoregulation: The process of maintaining a steady
body temperature under a variety of conditions.
Systems Involved:
Muscular*
Integument (skin)*
Respiratory
Circulatory
Nervous (hypothalamus in brain)
Endocrine (hormones, feedback)

8. A disruption of homeostasis can be harmful.
Homeostasis can be disrupted for several reasons.
sensors fail (don’t detect changes)
targets do not receive messages (nerve issues)
injury (overwhelm homeostatic controls)
illness (viruses or bacteria)
*Disruption of homeostasis can begin in one organ and cause a chain reaction in the others therefore causing a major body disturbance.

9. Organ systems must also work together to keep the organism healthy.
Organ systems work together to produce Vitamin D.
Thermoregulation maintains a steady body temperature. 1 2 3 4
Skin absorbs UV light
Liver produces inactive vitamin D
Kidneys produce active vitamin D
Active vitamin D used in bones
UV light

10. Body Temperature Regulation
Stimulus: Body Temp. Sensors
Body Temperature Regulation
Target:
Muscles/Glands
Commun.Syst:
Nerve Receptors
Control Syst.
=Brain