Homeostasis and Water Balance BIOL 1407

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

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

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

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

Response Effector Stimulus Integration Center

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): http://www.ehponline.org/members/2002/110p61-65frank/fig2.jpg

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

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

Strategies: Conformers vs. Regulators

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

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

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

Marine Bony Fish

Freshwater Fish

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

Marine Birds and Reptiles Salt Glands Marine Birds and Reptiles

Countercurrent Exchange

The End Unless otherwise specified, all images in this presentation came from: Campbell, et al. 2008. Biology, 8th ed. Pearson Benjamin Cummings.