Section 28-2
“Homeostasis”
Write everything that is
underlined
28.2 Mechanisms of Homeostasis
KEY CONCEPT
Homeostasis is the regulation and
maintenance of the internal
environment of the body
28.2 Mechanisms of Homeostasis
I. Homeostasis
Conditions within the body must remain within
a narrow range – like your body temperature
a. Homeostasis involves keeping the
internal environment within set ranges
28.2 Mechanisms of Homeostasis
b. Control systems help maintain
homeostasis.
–sensors gather data
–control center receives
data, sends messages
–communication system
delivers messages to
target organs, tissues
–targets respond to
change
pore
sweat
glands
hair
follicle
muscle
goose
bump
28.2 Mechanisms of Homeostasis
II. Feedback Loops
a. Negative feedback loops are
necessary for homeostasis
• Feedback compares current
conditions to set ranges.
• Negative feedback stops the
change
28.2 Mechanisms of Homeostasis
b. Negative Feedback Loop Example:
Holding
breath,
CO2 levels
rise
O2 / CO2 level
returns to normal
Control system
forces exhale,
inhale
28.2 Mechanisms of Homeostasis
c. Positive feedback increases change
–Example: Torn blood vessel
stimulates release of clotting factors
platelets
blood vessel
fibrin
clot
white blood cell
red blood cell
–growth hormones stimulate cell
division