1. Homeostasis and Water Balance
BIOL 1407

2. Homeostasis
Tendency to maintain a relatively constant internal environment despite changes in external environment
Crucial for survival

3. Why is Homeostasis Crucial?
Proper cell function depends on specific environmental conditions within internal environment:
Fluid that surrounds cells

4. Why is Homeostasis Crucial?
Membrane functions
Fluidity is affected by temperature
Membrane potential (charge) affected by chemical balance

5. Why is Homeostasis Crucial?
Proteins function within limited chemical range
Temperature pH

6. Response
Effector
Stimulus
Integration Center

7. Homeostatic Range Variable controlled within an acceptable range
Minimum and Maximum
Example of Temperature Fluctuations in Adult Male Mice (a) and Adult Male Humans (b):

10. Negative Feedback: Change in one direction  Change in opposite direction

11. Positive Feedback: Change in one direction  More change in same direction

13. Strategies: Conformers vs. Regulators

14. Water Balance
Regulates movement of water molecules between cells and internal environment

15. Osmoconformers Isoosmotic to surrounding seawater
As salinity of seawater changes  internal body fluid composition changes

16. Osmoregulators
Body fluids are not isoosmotic to surrounding environment
ATP must be used by organism to maintain the difference

17. Marine Bony Fish

18. Freshwater Fish

19. Terrestrial Animals
Water out through evaporation (most) and urine (little)
Water in through food (most) and drinking (little)
Photo Credit for Kangaroo Rat: Courtesy of Royal Alberta Museum, 2006, Wikimedia Commons

22. Marine Birds and Reptiles
Salt Glands
Marine Birds and Reptiles

23. Countercurrent Exchange

24. The End
Unless otherwise specified, all images in this presentation came from:
Campbell, et al Biology, 8th ed. Pearson Benjamin Cummings.