1. Homeostasis
SBI 4U

2. What is Homeostasis?
“… the process by which a constant internal environment is maintained despite changes in the external environment”
i.e. the body’s attempt to adjust to a fluctuating external environment

4. Homeostasis in the Human Body

5. Negative Feedback
process by which a mechanism is activated to restore conditions to their original state
prevents small changes from becoming too large
used more in the body than positive feedback
e.g. thermostat

6. Negative Feedback adjustment coordinating centre monitor normal range
regulator
adjustment

7. Positive Feedback the process by which a small effect is amplified
less common
reinforces change
e.g. contractions of uterus during birth (oxytocin)

8. Thermoregulation
thermoregulation = the maintenance of body temperature within a range that enables cells to function efficiently
hypothalamus = region of the vertebrate’s brain responsible for coordinating many nerve and hormone functions (“thermostat”)

9. Thermoregulation Response to heat stress: Response to cold stress:
Stimulus
Monitor
Coordinating Centre
Regulator
Adjustment
Response
heat
heat receptors in skin
brain (hypothalamus)
skin blood vessels dilate
sweating
-increased blood flow to skin & heat released
-evaporation
-body temperature decreases
Response to cold stress:
Stimulus
Monitor
Coordinating Centre
Regulator
Adjustment
Response
cold
cold receptors in skin
brain (hypothalamus)
skin blood vessels constrict
shivering
-hairs stand on end
-decreased blood flow to skin & heat conserved
-heat generation by increased metabolism
-body temperature increases

10. Research in Canada
When cells freeze, ice crystals destroy cell membranes BUT:
fish off the coast of Baffin Island in the Canadian Arctic have been found to contain a type of antifreeze [protein] in their blood that prevents ice crystals from forming (Scholander, 1957)
wood frogs found surviving in ice have high levels of glucose in their blood that act as an antifreeze (Storey, 2004)