1. HOMEOSTASIS

2. Homeostasis
Maintenance of a constant internal environment despite changes in external environment

3. WHAT ARE THE MAIN HOMEOSTATIC SYSTEMS DISCUSSED?
Blood pH
Oxygen/Carbon Dioxide
Body Temperature Control
Electrolytes (blood sugar)
Blood Pressure

4. HOW DOES HOMEOSTASIS WORK?
Homeostatic control systems detect stress or change and act to maintain EQUILLIBRIUM
They have 3 functional components:
Sensors/Monitors (senses stress compared to a SET POINT)
Coordinating centre
Regulator/ Effector (produces change)
 There are two main systems (Negative and Positive feedback)

5. Negative feedback mechanism:
Thermometer is the SENSOR that measures deviation from set point
Thermostat turns the regulator OFF when set point is achieved
Furnace and Air Conditioner are regulators which respond

6. Thermoregulation in the Body
The Hypothalamus is a gland in the brain which acts as our THERMOSTAT
It detects body temperatures outside the set range
It activates EFFECTORS using HORMONES to send the message

7. TEMPERATURE IN THE BODY
“Thermoregulation”
Coordinating
Centre
Sensors
Regulator
HYPOTHALAMUS (in brain) turns on COOLING system
FEEDBACK

8. TEMPERATURE IN THE BODY
“Thermoregulation”
Exercise:
We just looked at HEAT stress
What would happen if COLD stress occurred?
What would your sensors, coordinating centre and regulators be?
What result do you expect?
Explain how this is negative feedback
CHECK YOUR ANSWERS BY READING P338

9. TEMPERATURE IN THE BODY “Thermoregulation” in the COLD!
Sensor: Thermoreceptors in the skin detect dropping temperatures
Coordinating Center: Hypothalamus turns on warming system
Regulators:
Blood vessels in the skin constrict (shrink) decreasing blood flow to the skin, reducing heat loss from the skin
Muscle cells contract
Causes shivering
Smooth muscle surrounding hair follicles causes hair to stand on end (goosebumps!)
Result: Body temperature goes up!

10. Goosebumps!
Traps in warm air! Useful to animals that have thick coats of hair...

11. Net Result = Homeostasis

12. Weird Body Quirks Brain freeze
“Ice cream headaches” happen when something cold touches nerves in the roof of the mouth, triggering blood vessels in the front of your head to constrict -- producing pain. Try this quick pain relief trick: Press your tongue to the roof of your mouth to warm it up. 12

13. Less efficient homeostasis
“Ectotherms” (a.k.a. “cold-blooded” organisms must SEEK heat to be able to metabolize

14. Recall: Negative Feedback:
Brings fluctuating internal conditions back to NORMAL
Common for homeostasis
Positive Feedback:
sends messages to INDUCE a change
Not common

15. POSITIVE FEEDBACK AMPLIFICATION OF A SMALL EFFECT Rapid
Less common than negative feedback
e.g. hormones in birth ‘wake up’ the contraction process and stimulate other hormones to turn on

16. Feedback Loops
Figure 6-27: A positive feedback loop