What do you think of when you hear the term “homeostasis”? Why is it important? What are some “real world” examples?

Homeostasis Learning Target: explain internal feedback mechanisms for maintaining homeostasis

What is Homeostasis? The body’s attempt to maintain “normal” levels within your body - STABILITY Homeostasis is often referred to as a dynamic equilibrium- which is a mechanism to ensure that all body systems function within an acceptable range to sustain life. http://balancewines.wordpress.com/2009/12/

Homeostatic control systems 3 components: Receptor Integration Center Effector Stimulus sends a signal to the Receptor that the normal levels have changed. The Receptor then messages the Integration (control) Center to tell the Effector to restore normal balance. Stimulus Receptor Integrating Center Effector Change in balance

Core Temperature Humans have a normal temperature of around 36.2 to 37.2 degrees Celsius (97.9 – 98.6 degrees Fahrenheit) If body temperature goes above normal temperature - likely suffering from an infection and your body had to raise its temperature to fight off the infection. If body goes below this range -indicates hypothermia, therefore if left untreated it could lead to cell damage and possibly death. http://news.bbc.co.uk/2/shared/spl/hi/health/03/travel_health/diseases/html/sars.stm http://asimplebutimpossibletask.blogspot.com/

Homeostasis Example: household thermostat Explain… http://gasfurnaceprices.co.cc/

Homeostasis Example: household thermostat Stimulus- Thermostat Detects increase in temperature Receptor- Thermostat switches on AC (or heater) Integrating Center- AC Unit Effector-Thermostat detects temperature change beyond “normal” AC turns off Whole control system is called a negative feedback loop

EXAMPLE: Glucose and Insulin Negative Feedback Loop Boy eating cake Increases Glucose Levels (-) CYCLE 1 Stimulates β cells of pancreas to secrete insulin Lowers Blood Glucose levels Insulin stimulates the cells to take up glucose from the blood.

CYCLE 2 Low Blood Glucose Levels Glucagon is released EXAMPLE (cont…) Glucose and Insulin Negative Feedback Loop CYCLE 2 Low Blood Glucose Levels (-) Stimulated Alpha Cells in Pancreas High blood glucose levels and Cycle 1 continues Glucagon is released Glucagon stimulates liver cells to release glucose into the blood

Think-Pair-Share Take a minute to think of some examples in your daily life that use a Negative Feedback Loop...BY YOURSELF (write down your ideas) Share your ideas with your table group Agree on the best example at your table…share some of your ideas with the class

Homeostasis INDEPENDENTLY: Using your example of homeostasis…create a flow map to show how this feedback loop functions: Provide: Stimulus Receptor Integration Center Effector

Positive Feedback Mechanisms Homeostatic systems utilizing positive feedback exhibit two primary characteristics: Time limitation – Processes in the body that must be completed within a constrained time frame are usually modified by positive feedback. Intensification of stress – During a positive feedback process, the initial imbalance or stress is intensified rather than reduced as it is in negative feedback. Typical Positive Feedback Process Stress Sensor Control Center Intensifies Effector

Harmful Effects of Positive Feedback Positive feedback can be harmful. Two specific examples of these harmful outcomes: Fever can cause a positive feedback within homeostasis that pushes the body temperature continually higher. If the temperature reaches 113 degrees Fahrenheit, cellular proteins denature bringing metabolism to a stop and death. Chronic hypertension can favor the process of atherosclerosis which causes the openings of blood vessels to narrow. This, in turn, will intensify the hypertension bring on more damage to the walls of blood vessels.

1. What is homeostasis? Why is it called a dynamic equilibrium? 2. Describe these components of a homeostasis loop: stress, receptor, control center, effector, response. Using an example, put them in order. 3. What are the benefits of a negative feedback response? In what direction does a variable change as a result of a negative feedback response to a stress? 4. What are the benefits of a positive feedback response? In what direction does a variable change as a result of a positive feedback response to a stress? 5. What are the risks associated with positive feedback responses? 6. Draw 2 graphs to show negative & positive feedback responses. 7. Explain how positive feedback events can be “built into” a negative feedback loop. 8. What is homeostasis failure? What has happened with this occurs?

NEGATIVE FEEDBACK LOOP :: POSITIVE FEEDBACK LOOP Negative feedback occurs when the rate of the process decreases as the concentration of the product increases. Negative feedback controls the rate of a process to avoid accumulation of a product. Positive feedback (aka: “viscous” cycle) occurs when the rate of a process increases as the concentration of the product increases (both increase). The rate of a process will continuously accelerate under positive feedback.