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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Responses

  • Gualtiero
    What is rapid change in positve feedback?
    4 years ago
  • anne gersten
    Why positive feedback is more likely than negative feedback to disturb homeostasis?
    2 years ago
  • Ciro
    Is positive feedback is life threat?
    2 years ago
  • petros
    Is fever an example of positive feedback?
    2 years ago
  • eetu
    Is high fever positive feedback?
    2 years ago
  • jaakko
    How high fever is associated with positive feed back?
    2 years ago
  • ashlyn
    How fever is classified as positive feedback system?
    2 years ago
  • primrose
    Does homeostasis prevent internal change?
    1 year ago
  • ky
    How positive feedback increase fever?
    1 year ago
  • esko
    Why positive feedback is harmful?
    1 year ago
  • geronima
    Can a positive feedback vicious cycle set in when the body is 45°C?
    1 year ago
  • harrison
    Is generation of nerve impulse an examples of negative feedback?
    1 year ago
  • Sophia Oster
    Is a fever a positive feedback loop?
    1 year ago
  • Marko
    Is transmission of nerve signals an example of positive feeddback?
    1 year ago
  • tullio
    How positive feedback can be dangerous?
    1 year ago
  • hiwet elias
    How progression of fever is harmful positive feedback mechanism?
    10 months ago
  • jonas
    Why are some positive feedback mechanisms often harmful or even lifethreatening?
    10 months ago
  • eden fethawi
    Is a fever a positive or negative feedback?
    10 months ago
  • dawit
    How does a fever cause positive feedbacl?
    9 months ago
  • kirk
    Does a positive or negative feedback mechanism cause the body to have a fever?
    9 months ago
  • Gundahar
    What is positive feedback in physiology?
    8 months ago
  • poppy
    Why would it be wrong to say homeostasis prevents internal change?
    8 months ago
  • Adaldrida
    What are harmful effect positive feedback?
    8 months ago
  • Tom
    Why is positive feedback important in homeostasis?
    8 months ago
  • felix
    What effect does positive feedback have on homeostasis?
    8 months ago
  • suvi
    How positive feedback can be harmfull at time?
    8 months ago
  • callan ritchie
    What is the beneficial positive feedback in the system?
    7 months ago
  • eero
    Why is positive feedback mechanism is more likely than positive to disturb homeostasis?
    7 months ago
  • abi
    What kind of feedback is fever?
    7 months ago
  • LEO
    When does body undergo positive feedback mechanism?
    7 months ago
  • TAIMI
    Why is positive feedback harmful in homeostasis?
    6 months ago
  • duccio derose
    What is positive feed back concerning temperature?
    6 months ago
  • fastolph boffin
    How positive feedback can be harmful at times?
    6 months ago
  • pedro
    Is negative feedback likely to cause disease?
    6 months ago
  • ralf theissen
    What positive feedback in homeostasisi?
    6 months ago
  • kaj
    How fever becomes a life threatening process?
    6 months ago
  • Rezene Hamid
    Why is positive feedback system in homeostasis called as vicious cycle?
    4 months ago
  • mentha
    Why positive feedback system in human body called vicious cycle?
    4 months ago
  • Beatrice
    Why is positive feedback vicious and fatal?
    4 months ago
  • mckenzie
    Why is positive feedback mechanismst harmful?
    3 months ago
  • fatimah asfaha
    What happens with nerve in positive feedback loop in homeostasis?
    3 months ago
  • Nora
    Is fever a positive feedback on temperature?
    2 months ago
  • virginia
    What are the examples of positive feed back mechanism in physiology?
    2 months ago
  • KIM
    Why are positive feedback mechanisms generally harmful?
    2 months ago
  • Essi Autio
    How can positive feedback be detrimental?
    1 month ago
  • eberardo
    What is positive feedback in biology?
    8 days ago

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