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28.2 Mechanisms of Homeostasis
KEY CONCEPT Homeostasis is the regulation and maintenance of the internal environment.
28.2 Mechanisms of Homeostasis
Conditions within the body must remain within a narrow range.
• Homeostasis involves keeping the internal environment within set ranges.
28.2 Mechanisms of Homeostasis
Control systems help maintain homeostasis like ...
A. 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
hairfolliclemuscle
goosebump
28.2 Mechanisms of Homeostasis
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.
Negative Feedback Loop
Holding breath, CO2
levels rise,
Control system forces exhale, inhale
O2 / CO2 level returns to normal
28.2 Mechanisms of Homeostasis
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.
Ex. #2 = Growth hormones stimulate cell division
platelets
fibrin
white blood cellred blood cell
blood vessel
clot
28.2 Mechanisms of Homeostasis
Thermoregulation: The process of maintaining a steady
body temperature under a variety of conditions.
Systems Involved:
1. Muscular*
2. Integument (skin)*
3. Respiratory
4. Circulatory
5. Nervous (hypothalamus in brain)
6. Endocrine (hormones, feedback)
28.2 Mechanisms of Homeostasis
28.2 Mechanisms of Homeostasis
A disruption of homeostasis can be harmful.
• Homeostasis can be disrupted for several reasons.
1. sensors fail (don’t detect changes)
2. targets do not receive messages (nerve issues)
3. injury (overwhelm homeostatic controls)
4. 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.
28.2 Mechanisms of Homeostasis
• 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
28.2 Mechanisms of Homeostasis
Stimulus: Body Temp. Sensors
Commun.Syst:Nerve
Receptors
Control Syst.=Brain
Target:Muscles/Glands
Body Temperature Regulation
