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
pore
senses
sweat
B. Control Center= receives
glands
data, interprets info, sends
messages out.
hair
 brain
follicle
muscle
C. Communication System=
delivers messages to target
organs, tissues
PNS (e.g. motor neurons)
D. Targets = respond to change. goose
bump
muscles, glands (release
hormones)
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,
O2 / CO2 level returns to
normal
Control system forces
exhale, inhale
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.
platelets
blood vessel
fibrin
clot
white blood cell
red blood cell
Ex. #2 = Growth hormones stimulate cell division
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.
UV light
1
Skin absorbs UV light
2
Liver produces inactive vitamin D
3
Kidneys produce active vitamin D
4
Active vitamin D used in bones
28.2 Mechanisms of Homeostasis
Stimulus: Body
Temp. Sensors
Target:
Muscles/Glands
Body
Temperature
Regulation
Control Syst.
=Brain
Commun.Syst:
Nerve
Receptors