1. Homeostasis

2. Examples? Brainstorm levels in your body you should keep the same to for survival

3. Comparison Endocrine Nervous 1. stimulus 2. length of response
changes either _____for a long period of time or ____ for a short period of time that can results ______
Homeostasisis maintained through the action of 2 systems: endocrine system, nervous system
Comparison
Endocrine
Nervous
1. stimulus
2. length of response
3. location
4. time for response

4. Four Components of Homeostasis:
a quantity must be kept _________
a quantity has to _______ to be kept constant
something has to ______ the change (stimulus)
eg. receptor cells in the eye, skin (touch, pain, hot, cold, pressure), ears
something has to add or subtract—called a ______

5. Feedback Systems: 2 Types
Negative Feedback (more common)
Positive Feedback (less common)
response __________ or diminishes the original change
2 examples:
reaction to original change reinforces or ___________ the original change
3 examples:

7. FEEDBACK SYSTEMS STEPS
1.Stimulus—the change from the ideal condition; produces a response (which usually reduces the stimulus)
Eg. the thermostat in your house
A rise in temperaturethe furnace is turned off; a drop in temperature the furnace is turned on
2.Receptor (Sensor)—the sensory receptor cells or tissue which detects the change due to the stimulus and sends a signal to the control centre
3.Relay—the transmission of the message, via nerves, hormones or both, to the control centre

8. FEEDBACK SYSTEMS STEPS
4.Control Centre– receives information from the sensor and sends signals to the effector; decides what the response will be (usually located in an area of the brain)
5.Effector—the cells or tissue, usually a gland or muscle, which causes the response to happen
6.Response—an action (cell, tissue or organism level) that would not have occurred in the absence of the stimulus

9. HOMEWORK
Read P
Do P. 348 #6, 9, 10
Label the diagram on the handout
(Reference chapter 9 from textbook P. 390-)

10. Other Questions (if time) 1
Other Questions (if time) 1. What is the difference between positive and negative feedback?
NEGATIVE FEEDBACK:
make adjustments to bring the body back within an acceptable range
EXAMPLE: household thermostat is an example of such a system
an activity changes some condition in the internal environment that, in turn, triggers a response that reverses the changed condition.
Positive feedback:
less common in the body
Whereas negative feedback systems are designed to resist change, positive feedback systems reinforce change
Positive feedback systems move the controlled variable even further away from a steady state
EXAMPLE: Using the furnace and temperature example, the room would get progressively hotter.

11. #2. During lactation, the suckling by the baby stimulates the production of oxytocin, which in turn causes contraction of smooth muscle surrounding the milk duct, causing milk to flow. The flow of milk increases the suckling by the baby and more oxytocin is produced. A) Identify the feedback system described above. B) What would end the feedback loop?
ANSWER
(a) Positive feedback system
(b) The baby is full and stops suckling.

12. Why is exercise at high temperatures dangerous?
3. Every year some deaths of athletes are linked with extreme exercise in hot, humid conditions.
Why is exercise at high temperatures dangerous?
How could you help these athletes?
ANSWER
(a) Core body temperature increase, causing enzymes to denature. This shows enzyme- catalyzed reactions. If this occurs in too many cells, organ failure results.
(b) Possible suggestions include the following:
Increase the intake of water to cool the body
Periodically stop high intensity exercise to allow the body to cool
Monitor body temperature during exercise
Prohibit high- intensity exercise at very high ambient air temperatures

13. #4. Boxers have been known to take laxatives to help them meet the weight restrictions of lower fighting classes.
How would taking laxatives help them lose weight?
Why might this practice be dangerous?
#9. (a) Laxatives increase water loss. (Laxatives stimulate the bowel to empty after food and calories have been absorbed, therefore, only water is lost.) This loss is temporary because once the body rehydrates, the water weight loss comes back.
(b) There would be a decrease in body fluids (dehydration) and a decrease in blood pressure. The decrease in blood pressure also upsets the balance of electrolytes in the body. The disturbance in electrolyte balance can damage the tissues and muscles of the body, even those around the heart. Damages to the muscle around the heart can lead to death.

14. causes an increase in body temperature (hyperthermia)
#5. Drugs such as ecstasy interfere with the feedback mechanism that helps maintain a constant temperature. Explain why these drugs are dangerous.
causes an increase in body temperature (hyperthermia)
increase in body temperature with physical activity such as dancing and a warm environment, the situation can become worse.
increase in blood pressure and heart rate can lead to kidney or heart failure, strokes and seizures.