1. What would kill you first if your body’s homeostasis systems failed
What would kill you first if your body’s homeostasis systems failed? Think about which organ systems do what as you rank them.
A change in body temperature
An increase in the concentration of carbon dioxide
A change in the concentration of oxygen
A change in concentration of electrolytes
An increase in the concentration of waste
A change in concentration of blood sugar

2. The kidneys sense that the oxygen levels in the blood are low
The kidneys sense that the oxygen levels in the blood are low. The kidney sends a hormone signal to the bone marrow to make more red blood cells. The number of red blood cells increases, so more oxygen is carried in the blood. A.
This is a positive feedback loop B.
This is a negative feedback loop C.
This is not a feedback loop

3. 10. An example of feedback is seen in blood clotting
10. An example of feedback is seen in blood clotting. Part of the complex biochemical pathway of clotting is the production of an enzyme that forms the matrix of the blood clot, but also speeds up the production of still more thrombin. That is, it has a self- catalytic , self-accelerating effect, so that once the clotting process begins, it runs faster and faster until, ideally, bleeding stops. Thus, this positive feedback loop is part of a larger negative feedback loop, one that is activated by bleeding and ultimately works to stop the bleeding. A.
This is a positive feedback loop B.
This is a negative feedback loop C.
This is not a feedback loop

4. What type of feedback loop is this?
Feedback is seen in protein digestion, where the presence of partially digested protein in the stomach triggers the secretion of hydrochloric acid and pepsin, the enzyme that digests protein. Pepsin digests proteins, casing more HCl and pepsin to be released.

5. INTRODUCTION TO HOMEOSTASIS

6. Important variables within the body:
blood sugar
fluid balance
body temperature
oxygen levels
blood pressure pH
These variables must stay within certain ranges.
Changes in the external environment can cause these variables to change.

7. Homeostasis:
The process by which a constant internal environment is maintained despite changes in the external environment.

8. The hypothalamus Part of the brain
Often serves as the co-ordinating centre:
Receives messages from monitors
Initiates a hormonal/nervous response

9. Dynamic equilibrium Homeostasis is also called dynamic equilibrium:
Conditions do fluctuate, but within an acceptable range

10. How is dynamic equilibrium maintained? Feedback systems
Negative feedback
Positive feedback

11. Negative feedback
Negative feedback: Response triggered by changed conditions serves to reverse the change
E.g., Body temperature increases  Skin blood vessels dilate  Body temperature decreases

12. Normal body temperature
Body temperature increases
Hypothalamus sends a message to blood vessels
Skin blood vessels dilate
Body temperature decreases
Normal body temperature

13. Example: Blood Pressure Regulation

14. Positive feedback
Positive feedback: The response triggered by changing conditions serves to move the variable even further away from its steady state
E.g., uterine contractions are stimulated by oxytocin  baby moves towards cervix  more oxytocin is released

16. Maintaining body temperature
Thermoregulation
Maintaining body temperature

18. Body temperature Average human body temperature: 37°C
Core body temperature is slightly higher
Interindividual variation

19. Thermoregulation
Thermoregulation: The maintenance of body temperatures within a range that enables cells to function effectively
Recall: Enzymes have optimal temperatures
High temperatures can denature proteins

20. Types of temperature stress
Heat stress
Cold stress

21. Response to Heat Stress

22. Response to Heat Stress
Co-ordinating centre is the hypothalamus
Responses:
Skin blood vessels will dilate
Sweat glands will produce perspiration
Both responses serve to lower body temperature  Return to normal range

23. Response to Cold Stress

24. Response to Cold Stress
Co-ordinating centre is the hypothalamus
Responses:
Skin blood vessels will constrict
Skeletal muscle will contract rapidly (shivering), increasing metabolism
Smooth muscle around hair follicles will contract, producing goosebumps
Responses serve to raise body temperature  Return to normal range

25. Prolonged exposure to cold stress
May cause an increase in the rate of metabolism
Special fat cells called “brown fat”
Particularly important for babies

26. Hypothermia: Occurs when core body temperature drops below normal range.
Usually results in coma, then death 

27. Summary of thermoregulation
Stimulus
Physiological response
Adjustment
Cold
constriction of blood vessels in skin
hairs on body erect
shivering
heat is conserved
heat is generated by increasing metabolism
Heat
dilation of blood vessels in skin
sweating
heat is released

28. Homework
pg.111 Answer All Questions