Study Questions for Lecture 1 1. a. Define Homeostasis Homeostasis is the maintenance of certain key physiological variables within narrow limits despite changing conditions. b. Physiological variables are always regulated within a range. As the text puts it, they are kept “relatively constant”. Why is it good to have some “slack” in homeostasis? Some slack is useful, as more precise control requires greater energy expenditure, better sensors and better effectors (think of your parents’ role as controllers!). Some slack is also useful to allow for changing conditions without resetting a setpoint. The relative amount of “slack” (the “narrowness” of the limits) varies among systems– watch as we study various ones. 2. a. Because plasma and interstitial fluid mix readily with each other, physiologists often classify plasma volume plus interstitial fluid volume as ‘extracellular fluid volume’. What percentage of total body water is in ‘extracellular fluid’?
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