1. LT- Today, we will analyze how feedback mechanisms (loops) help to maintain homeostasis by applying our understanding to how glucose levels are controlled in the body. What is a feedback mechanism? What are the two feedback mechanisms? How do feedback mechanisms work in controlling homeostasis?

2. Homeostasis- in the body, is a stable internal environment. For example, a normal body temperature for a human is 98.6  F. This homeostasis. There is a range just above and just below this temperature that is safe BUT 95  F is too far below homeostasis and this is when hypothermia sets in. The person can loose limbs or die if the temperature is not brought back to homeostasis. 103  is too high above homeostasis and this is when the person’s temperature can cause organs to shut down and death.

3. To maintain homeostasis, your body has a diversity of feedback mechanisms that detect deviations in the body’s internal environment and make corrective actions. Feedback Mechanism- mechanisms that regulate changes to maintain a stable internal environment. They have three steps *1 st Receptor- (such as a nerve when you are touched or the cells of the pancreas that monitor glucose level) detects change in the internal environment. *2 nd Control Center- (such as the brain or an organ), selects a response to the information from the receptor. *3 rd Effector- (such as a muscle, gland, or an organ) carries out the response to bring the body back to homeostasis and this effect is detected by the receptor, and the process starts again.

4. The 2 Types of Feedback Mechanisms (Loops) Negative feedback- a change in one direction of a feedback mechanism that stops further change in that direction. Positive feedback- a feedback mechanism that continues further change in a direction.

5. Example: Speed limit Example: Heat from a thermostat example

6. Test Topics- Cellular Respiration Systems that work together in Cellular Respiration Biomolecules Transport through the cell membrane Proteins of the cell membrane (especially receptor proteins) Plant cells vs Animal Cells Photosynthesis Feedback mechanisms

7. Glucose ____ Receptor- Pancreas (detects high sugar/glucose) Control Center- Pancreas releases Insulin (a hormone that interacts with the liver (the shape fits with receptor proteins on the liver) ) Effector- Liver brings in glucose from the bloodstream as a reaction to the insulin and stores it as glycogen in the vacuoles. Blood sugar goes down towards homeostasis.

8. Glucose ____ Receptor- Pancreas (detects high sugar/glucose) Control Center- Pancreas releases Glucagon (a hormone that interacts with the liver (the shape fits with receptor proteins on the liver) ) Effector- Liver breaks down glycogen into glucose as a reaction to glucagon and releases glucose into the bloodstream. Blood sugar goes up back towards homeostasis.

9. Regulating Blood Sugar (Glucose) Levels in the Body- Negative Feedback Mechanism 1.A person eats an apple Pancreas- the organ that detects high glucose. Insulin- the hormone released by the pancreas to bring glucose levels down in the bloodstream. Liver- the organ that takes in glucose from the bloodstream in response to insulin. Glycogen- the carbohydrate that glucose is stored in in the vacuole until needed later.

10. 2. A person is hungry. Pancreas- the organ that detects low glucose. Glucagon- the hormone released by the pancreas to bring glucose levels up in the bloodstream. Liver- the organ that breaks down glycogen in response to the glucagon. Glycogen- the carbohydrate that is broken down into glucose and released into the bloodstream by the liver.

11. Blood Glucose Control Insulin- lowers blood glucose (tells liver to convert glucose into glycogen for future use) Glycogen- increases blood glucose (stimulates the liver to break down glycogen) HungryReceptors sense a change Glucose in the blood is low Control center secretes glucagon Pancreas releases the hormone glucagon into the blood Effector Glucagon signals the liver to breakdown glycogen and release the glucose into the blood