9/2/2015
Adapted from “Homeostasis,” Liberty Senior High School, Mr. Knowles
 “Homeo”‐ same.
“‐stasis”‐ standing or status.
 To maintain a relatively constant internal environment (set point).
 External environment has many variables‐temp., pH, water, etc.
 Is a dynamic state of equilibrium (constantly adjusting)
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 Stimulus‐ an environmental change that signals the body in some way.
 Response‐ the change in cellular activity the body makes in order to maintain homeostasis. Photo: mediahex.com
 Two Mechanisms:
1. Autoregulation (intrinsic)‐ activities of a cell, tissue or organ change automatically when faced with environmental variation. Ex. Tissues experiencing oxygen deprivation during exercise release chemicals, which cause a local dilation of blood vessels
Often happen before nervous system even detects changes
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 Receptor‐ sensor that monitors and responds to changes in the environment (called “stimulus”).
 Control/Integrating Center‐ receives and processes the information supplied by the receptor and determines appropriate response.
 Effector‐ cell or organ that responds to the commands of the control center and either depresses or enhances the original stimulus.
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 Two Mechanisms:
2. Extrinsic Regulation‐activities of the nervous or endocrine systems affect many systems at the same time.
Ex. Exercise induces the nervous system to increase your heart rate and reduce blood flow to unessential organs
If we keep running for a long period of time, the extrinsic controls will kick in to also help regulate the changes going inside the body: Temp, glucose levels, etc.
 Chemical reactions within cells work most effectively within a certain range of conditions (temp., pH, salt, energy).
 Organ systems work together to maintain this stable internal environment.
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1.
Negative Feedback‐ when the effector(s) activated by the control center depress stimulus. Most common feedback systems: thermoregulation, salt, water, pH, blood sugar.
2.
Positive Feedback‐ initial stimulus produces a response that exaggerates or enhances its effects. Less common.
Ex. Labor contractions, Blood clotting
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1. A disturbance in homeostasis (a disease or illness)
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