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Homeostasis and Feedback

Homeostasis and Feedback. Homeostasis: processes that maintain the relatively stable internal environment that keeps an organism alive Feedback: process that allows the body to sense changing internal conditions and respond to them. How Feedback Works. A STIMULUS occurs

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Homeostasis and Feedback

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  1. Homeostasis and Feedback Homeostasis: processes that maintain the relatively stable internal environment that keeps an organism alive Feedback: process that allows the body to sense changing internal conditions and respond to them

  2. How Feedback Works • A STIMULUS occurs Examples are: A change in blood pressure A change in body temperature An injury to the body Etc……………

  3. A RECEPTOR picks up the stimulus Examples:Receptors in blood vessels that sense being stretchedReceptors in the brain that sense blood temp., CO2 level, sugar level….Damage to cells that release proteins that are normally in the cell.

  4. A message is sent to the CONTROL CENTER (the brain) or directly to an EFFECTOR. The control center will send a response message to an Effector.

  5. EFFECTOR: A tissue or organ in the body that produces some type of action in response to the message from the receptor or the control center.Examples: A gland that begins to release a hormoneor stops releasing a hormone. A muscle that begins to contract faster or slower.

  6. RESPONSE – maintains homeostasis

  7. Two Types of Feedback Positive Feedback Negative Feedback Definition: Change away from initial conditions When does this happen? Corrects a situation that has moved away from homeostasis. • Definition: Change toward initial conditions • When does this happen? When some critical process must be completed

  8. Example of Positive FeedbackBlood Clotting

  9. Watch an animation of blood clotting:http://www.mhhe.com/biosci/esp/2002_general/Esp/folder_structure/tr/m1/s7/trm1s7_3.htm

  10. Example of Negative FeedbackLow Blood Pressure • Dehydration leads to low blood pressure • Low blood pressure detected by baroreceptors on the heart • Those baroreceptors send message to brain • The brain sends a message to both the blood vessels and the heart • Arteries constrict and heart rate increases • Result: Normal blood pressure

  11. Fill in a chart over negative feed back and watch an animation over low blood pressure http://www.johnwiley.net.au/highered/interactions/media/Foundations/content/Foundations/homeo2c/bot.htm

  12. Identify the following examples as positive or negative feedback and answer the questions on the Homeostasis Worksheet

  13. The control of sugar levels in the blood:

  14. Childbirth As a baby moves towards the birth canal, it presses against the .pressure receptors in the muscular part of the uterus. These receptors evoke a release of oxytocin from the brain (and maybe also the placenta). When the oxytocin reaches responsive receptors in the muscles of the uterus it will increase muscular tension thus increasing stimuli to the pressure receptors. This goes on as "labor" until the pressure is relieved: the baby is born -- oxytocin is no longer evoked and labor contractions cease. Baby’s head presses Message sent to Oxytocin released Contractions pressure receptors the brain. from pituitary Increase in the uterus wall “time for baby to glandbe born” More pressure from baby on uterus wall.

  15. The Control of Body TemperatureCooling mechanisms – External blood vessels dilate and more blood flows to the skin losing heat, sweating beginsWarming Mechanisms – External blood vessels constrict and more blood stays in the internal part of the body keeping internal organs warm, shivering begins

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