BIOL 219 Spring 2013

Lecture outline for “Homeostasis” What is Homeostasis?

Claude Bernard Walter Cannon

Homeostatically-controlled variables Feedback mechanisms

Negative Feedback Components of a negative feedback loop Examples

Positive Feedback Example - childbirth

Feedforward Mechanism Pavlov’s dogs

Homeostasis gone awry Objectives: (1) Define homeostasis. (2) Identify the major components of feedback loops and their functions. (3) Compare and contrast positive and negative feedback loops. (4) Do you think that it is more efficient to have antagonistic effectors or a single effector to “maintain” the set point of a homeostatically-controlled variable? (5) What is the major difference between feedforward mechanisms and feedback loops? (6) Given a specific scenario, you should be able to identify whether a variable is controlled by negative feedback, positive feedback, or a feedforward mechanism. You should also be able to identify the receptor, integrator, and/or effector organ(s) in this scenario as well. (7) Consider some of the homeostatically-controlled variables that we identified in class. What are some of the consequences if we are no longer able to maintain these variables within narrow limits?