HOMEOSTASIS

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

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

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)

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

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

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

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

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!

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

Net Result = Homeostasis

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

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

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

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

Feedback Loops Figure 6-27: A positive feedback loop