1. Homeostasis and Feedback Notes

2. Homeostasis Homeo = Similar Stasis = State Homeostasis is the maintenance of a stable internal environment. Necessary for proper function of enzymes that carry out all metabolic processes Involves all organ systems

3. Components The receptor monitors changes in the environment. A message is sent to the control center. The control center determines the set point. It analyzes information and determines a response. The set point is the level at which a variable needs to stay. For example, the temperature set point is: The control center then sends information to the effector. The effector performs the response.

5. Feedback The effector’s response creates a feedback to the variable. Feedback can be either positive or negative. Most feedback mechanisms are negative feedback. Negative feedback mechanisms work to reduce the stimulus or shut it off. Examples – body temperature, blood sugar Positive feedback mechanisms are rare and work to increase the stimulus. Two examples of positive feedback are blood clotting and contractions during childbirth.

6. Thermostat Analogy Body Receptors/Sensors = sensory nerves Control Center = Hypothalamus in brain send signals to muscles via nerves Effector = muscles Long term: endocrine system increases thyroid activity to raise metabolic rate to increase heat production from cellular respiration

7. Body Temperature Effectors Blood flow reduced to arms and legs, keeps blood in torso, Muscles at follicles raise hairs, Skeletal muscles contract (shiver) generate heat Heart rate slows to keep blood concentrated in core body Skeletal muscle adjust body curls up

9. Negative Feedback Your body gets too hot. Response: Your body sweats to cool down. Time Temperature

10. Positive feedback Reinforces the original stimulus – pushing conditions further from the normal Less common as it can get out of control and will not stop until stimulus is removed Increases chaos in body systems Examples – blood clotting and child birth

11. Clotting signals continue until clot is complete

12. Practice: Draw a graph for each situation. 1.You are too cold, so you start to shiver. 2.You drink too much water, so you pee it out. 3.You lose too much water, so your body slows down urine production.

13. Negative Feedback Loop Your body is too hot, so you sweat to cool down. (receptor) Temperature - + Sweat (effector)

14. Practice: Draw a negative feedback loop for each situation. 1.You are too cold, so you start to shiver. 2.You drink too much water, so you pee it out. 3.You lose too much water, so your body slows down urine production.