Homeostasis And how organisms react to stimuli

In your ISN, write these terms – fill in as we go Homeostasis StimulusResponseFight or Flight (Definitions) (picture/ example)

Stimulus An action or condition that provokes a response

Response Any behavior of a living organism that results from an external (outside the body) or internal (inside the body) stimulus

Example: Stimulus / Response Internal stimulus Scared Response Heart beats faster, breathing is faster (triggers the response of many systems) External stimulus Touching a hot stove Response Moving your hand

What is Homeostasis? The tendency of an organism or cell to maintain a balanced state so as to maintain health and functioning

Homeostasis involves keeping the internal environment within set ranges, such as internal temperature in mammals.

Steps involved in maintaining homeostasis: –sensors gather data –control center receives data, sends messages –communication system delivers messages to target organs, tissues –targets respond to change pore sweat glands hair follicle muscle goose bump

Feedback Loops Feedback compares current conditions to set ranges. Negative feedback loops stop the change; output reduces the original effect of the stimulus Positive feedback loops increase change; the output enhances the original stimulus

Your household thermostat

Positive Feedback A good example of a positive feedback mechanism is blood clotting. Once a vessel is damaged, platelets start to cling to the injured site and release chemicals that attract more platelets. The platelets continue to pile up and release chemicals until a clot is formed.

Fight of Flight The body’s reaction related to physiological changes in the body due to stress

Wired to survive….