Homeostasis PDF

Organ Systems? 2 Function and Mechanism • Both explored by physiologists • Function asks “why” questions • “Why do we breathe?” • “Why does blood flow from arteries to your organs?” • Mechanism explains “how” • “How do we breathe?” • “How does blood flow?” 3 Homeostasis • maintaining a relati...

Organ Systems? 2 Function and Mechanism • Both explored by physiologists • Function asks “why” questions • “Why do we breathe?” • “Why does blood flow from arteries to your organs?” • Mechanism explains “how” • “How do we breathe?” • “How does blood flow?” 3 Homeostasis • maintaining a relatively stable internal environment • what does the word “environment” mean? • …so what’s the “internal environment”? • ECF • a buffer between the living cells and the world outside the body 4 A Dynamic Steady State • not an equilibrium • a dynamic disequilibrium 5 Control Systems • regulated variables have set-points, or optimal values • variables are kept within ranges by control systems • local control systems regulate and affect tissues they are in • reflex control systems can be more long-distance (and may be more complex) 6 Reflex Pathways Involve 2 Loops • Response loop • starts with a stimulus • Feedback loop • influences the input • may increase or decrease the stimulus • may block the sensor or inhibit the input 7 Feedback May Be Negative or Positive • Negative feedback loops are homeostatic • stabilize the variable around the setpoint • Positive feedback loops are not • enhances or reinforces the originating stimulus 8