Positive Feedback and Rapid Change

Positive feedback is a self-amplifying cycle in which a physiological change leads to even greater change in the same direction, rather than producing the corrective effects of negative feedback. Positive feedback is often a normal way of producing rapid change. When a woman is giving birth, for example, the head of the baby pushes against her cervix (the neck of the uterus) and stimulates its nerve endings (fig. 1.13). Nerve signals travel to the brain, which, in turn, stimulates the pituitary gland to secrete the hormone oxytocin. Oxytocin travels in the blood and stimulates the uterus to contract. This pushes the baby downward, stimulating the cervix still more and causing the positive feedback loop to be repeated. Labor contractions therefore become more and more intense until the baby is expelled. Other cases of beneficial positive feedback are seen later in the book; for example, in blood clotting, protein digestion, and the generation of nerve signals.

Frequently, however, positive feedback is a harmful or even life-threatening process. This is because its self-amplifying nature can quickly change the internal state of the body to something far from its homeostatic set point. Consider a high fever, for example. A fever triggered by infection is beneficial up to a point, but if the body temperature rises much above 42°C (108°F), it may create a dangerous positive feedback loop (fig. 1.14). This high temperature raises the metabolic rate, which makes the body produce heat faster than it can get rid of it. Thus, temperature rises still further, increasing the metabolic rate and heat production still more. This "vicious circle" becomes fatal at approximately 45°C (113°F). Thus, positive feedback loops often create dangerously out-of-control situations that require emergency medical treatment.

Before You Go On

Answer the following questions to test your understanding of the preceding section:

  1. List four biological criteria of life and one clinical criterion. Explain how a person could be clinically dead but biologically alive.
  2. What is meant by dynamic equilibrium? Why would it be wrong to say homeostasis prevents internal change?
  3. Explain why stabilizing mechanisms are called negative feedback.
  4. Explain why positive feedback is more likely than negative feedback to disturb homeostasis.

Saladin: Anatomy & 1. Major Themes of Text © The McGraw-Hill

Physiology: The Unity of Anatomy and Physiology Companies, 2003

Form and Function, Third Edition

Chapter 1 Major Themes of Anatomy and Physiology 19

Oxytocin carried in bloodstream to uterus

  • LOxytocin stimulates uterine contractions and pushes fetus toward cervix
  • 3) Brain stimulates pituitary gland to secrete oxytocin
  • 3) Brain stimulates pituitary gland to secrete oxytocin
(1 Head of fetus pushes against cervix
  • Nerve impulses from cervix transmitted to brain
  • Nerve impulses from cervix transmitted to brain

Figure 1.13 Positive Feedback in Childbirth. This is one of several cases in which positive feedback produces beneficial rapid change.

Positive Feedback Fever
Figure 1.14 Positive Feedback in Fever. In such cases as this, positive feedback can produce a life-threatening loss of homeostatic control.
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  • Gualtiero
    What is rapid change in positve feedback?
    5 years ago
  • anne gersten
    Why positive feedback is more likely than negative feedback to disturb homeostasis?
    3 years ago
  • Ciro
    Is positive feedback is life threat?
    3 years ago
  • petros
    Is fever an example of positive feedback?
    3 years ago
  • eetu
    Is high fever positive feedback?
    3 years ago
  • jaakko
    How high fever is associated with positive feed back?
    3 years ago
  • ashlyn
    How fever is classified as positive feedback system?
    3 years ago
  • primrose
    Does homeostasis prevent internal change?
    3 years ago
  • ky
    How positive feedback increase fever?
    3 years ago
  • esko
    Why positive feedback is harmful?
    3 years ago
  • geronima
    Can a positive feedback vicious cycle set in when the body is 45°C?
    3 years ago
  • harrison
    Is generation of nerve impulse an examples of negative feedback?
    3 years ago
  • Sophia Oster
    Is a fever a positive feedback loop?
    3 years ago
  • Marko
    Is transmission of nerve signals an example of positive feeddback?
    3 years ago
  • tullio
    How positive feedback can be dangerous?
    3 years ago
  • hiwet elias
    How progression of fever is harmful positive feedback mechanism?
    3 years ago
  • jonas
    Why are some positive feedback mechanisms often harmful or even lifethreatening?
    2 years ago
  • eden fethawi
    Is a fever a positive or negative feedback?
    2 years ago
  • dawit
    How does a fever cause positive feedbacl?
    2 years ago
  • kirk
    Does a positive or negative feedback mechanism cause the body to have a fever?
    2 years ago
  • Gundahar
    What is positive feedback in physiology?
    2 years ago
  • poppy
    Why would it be wrong to say homeostasis prevents internal change?
    2 years ago
  • Adaldrida
    What are harmful effect positive feedback?
    2 years ago
  • Tom
    Why is positive feedback important in homeostasis?
    2 years ago
  • felix
    What effect does positive feedback have on homeostasis?
    2 years ago
  • suvi
    How positive feedback can be harmfull at time?
    2 years ago
  • callan ritchie
    What is the beneficial positive feedback in the system?
    2 years ago
  • eero
    Why is positive feedback mechanism is more likely than positive to disturb homeostasis?
    2 years ago
  • abi
    What kind of feedback is fever?
    2 years ago
  • LEO
    When does body undergo positive feedback mechanism?
    2 years ago
    Why is positive feedback harmful in homeostasis?
    2 years ago
  • duccio derose
    What is positive feed back concerning temperature?
    2 years ago
  • fastolph boffin
    How positive feedback can be harmful at times?
    2 years ago
  • pedro
    Is negative feedback likely to cause disease?
    2 years ago
  • ralf theissen
    What positive feedback in homeostasisi?
    2 years ago
  • kaj
    How fever becomes a life threatening process?
    2 years ago
  • Rezene Hamid
    Why is positive feedback system in homeostasis called as vicious cycle?
    2 years ago
  • mentha
    Why positive feedback system in human body called vicious cycle?
    2 years ago
  • Beatrice
    Why is positive feedback vicious and fatal?
    2 years ago
  • mckenzie
    Why is positive feedback mechanismst harmful?
    2 years ago
  • fatimah asfaha
    What happens with nerve in positive feedback loop in homeostasis?
    2 years ago
  • Nora
    Is fever a positive feedback on temperature?
    2 years ago
  • virginia
    What are the examples of positive feed back mechanism in physiology?
    2 years ago
  • KIM
    Why are positive feedback mechanisms generally harmful?
    2 years ago
  • Essi Autio
    How can positive feedback be detrimental?
    2 years ago
  • eberardo
    What is positive feedback in biology?
    2 years ago
  • Sanna
    Can positive feedback explain homeostasis?
    1 year ago
  • yohannes
    Why is cancer a positive feedback?
    1 year ago
    Is cancer positive or negative feedback?
    1 year ago
  • taimi
    How postive feedback can be harmfull at time?
    1 year ago
  • sinit
    Why are some positive feedback mechanisms dangerous?
    1 year ago
  • ANN
    Is cancer postive or negative feedback?
    12 months ago
  • lillian wheeler
    Why are positive feedback mechanism generally harmful?
    9 months ago
  • Herbert
    Why is positive feedback life threatening?
    8 months ago
  • kevin
    What is postive feedback mechanism?
    7 months ago
  • iiro
    What is positive feed bake related to homeostasis?
    6 months ago
  • laura
    How can positive feedback to the body be deadly?
    5 months ago
  • anthony
    Are postive feedback mambranes alwasy damaging to the body?
    4 months ago
  • eberardo
    Is a fever a positive feeback?
    4 months ago
    Is postive feedback beneficial in most cases?
    4 months ago
  • scott
    Is sex a positive feedback loop in the body?
    4 months ago
  • sointu salo
    Why positive feedback is likely to cause a loss of homeostasis?
    4 months ago
  • Fnan
    Why is positive feedback related to disease?
    4 months ago
  • zufan
    Which feedback cycle is more likely to PREVENT homeostasis?
    4 months ago
    Why is cancer a positive feedback in homeostasis?
    4 months ago
  • alberto
    How is transmission of nerve impulses a positive feedback?
    4 months ago
  • prisca
    Is generation of nerve signal positive feedback?
    3 months ago
  • hailey
    Is gaining weight a positive feedback mechanism?
    2 months ago
  • Saare
    What is positive feedback in cardiovascular disease?
    2 months ago
  • asmara
    How does positive feedback mechanism affects a person suffering from heart attack?
    2 months ago
    Why positive feedback is disastrous?
    2 months ago
  • melilot
    Which feedback loop is more likely to cause disease and death?
    5 days ago
  • Berylla Hayward
    Why do you think positivefeedback mechanisms have the potential to be harmful?
    2 days ago
  • giovanni
    Does positive feedback occur with only life threatening issues?
    1 day ago
  • Jai
    Is a high fever a positive or negative feedback mechanism?
    1 day ago
  • winta gabriel
    Why is thirst not a positive feedback mechanism?
    1 day ago
  • medhanie
    How can positive feedback loop be harmful with fevers?
    1 day ago

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