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Difference Between Positive Feedback and Negative Feedback

Regarding biological mechanisms, positive and negative feedback are known products of molecular and physiological processes. Both are control systems that are involved in the body’s homeostasis or the propensity of organisms to maintain balance and regulate their internal environment. Without these feedbacks, an organism would lose its capacity to self-regulate. Basically, positive feedback amplifies the original stimulus while negative feedback slows it down. The following concepts expound on their differences.

 

What is Positive Feedback?

In positive feedback, there is a direct positive correlation between the concentration and the process rate. One good example is how the endocrine system regulates the release of its hormones. Particularly, oxytocin is a hormone released by the pituitary gland during child birth. It is crucial in labor and normal delivery. As the contractions increase, more oxytocin is being produced until the child is born. Also, this chemical has been associated with social bonding. For instance, hugging someone stimulates the release of oxytocin. Someone who gets (and gives) lots of hugs also experiences an enhanced production of the said hormone.

The following enumeration outlines the phases involved in a negative feedback:

  1. A stimulus disturbs the originally controlled variables.
  2. Receptors detect the change.
  3. The information travels through the system’s pathway towards the control center.
  4. The control center determines the appropriate action and sends information to effector cells.
  5. The initial deviation is intensified.

What is Negative Feedback?

Negative feedback controls the process rate to prevent substance accumulation. Contrary to positive feedback, it reflects a negative correlation between the concentration and process rate. Most homeostatic procedures involve negative feedback as most mechanisms achieve equilibrium by going back to their original states. When the brain detects an internal disruption, it sends messages via the nervous system that activate pertinent organs to return the values within normal range.

This mechanism is often likened to a heating system which gets turned up if the perceived temperature is too low and vice versa. For example, the pancreas releases two hormones with opposite functions. Insulin lowers down blood sugar levels while glucagon raises it up. When the body detects that it has too much sugar, the pancreas is prompted to release insulin and only stops when balance is achieved; hence, negative feedback. Likewise, the pancreas is prompted to release glucagon when it senses that the body has very low sugar and only stops when the body has returned to its usual state.

The following enumeration outlines the phases involved in a negative feedback:

  1. The original state is disturbed.
  2. Receptors detect the change.
  3. The information travels through the system’s pathway towards the control center.
  4. The control center determines the appropriate action.
  5. Equilibrium is restored by counteracting the excessive production rate.

 

Difference between Positive and Negative Feedback

  1. Frequency of Positive and Negative Feedback

As compared to positive feedback, negative feedback occurs more frequently among the body’s homeostatic mechanisms as many diseases is caused by the disruption of the original systemic state. It is then more familiar while positive feedback is less observed as it is less intuitive.

  1. Mechanism involved in Positive and Negative Feedback

The mechanism of positive feedback supports a higher rate of production or process as an action likewise increases. Thus, the result of a reaction is magnified. On the other hand, negative feedback inhibits the rate as a certain state is enhanced. Hence, the result of a reaction is inhibited.

  1. Stability of Positive and Negative Feedback

As compared to positive feedback, negative feedback is more closely associated with stability as it lessens the effects of agitations. On the contrary, positive feedback supports exponential growth which may lean towards instability.

  1. Change in Positive and Negative Feedback

Negative feedback generally resists changes as it makes adjustments to bring back the system to its original state. On the other hand, positive feedback usually supports change as a small effect is enhanced.

  1. Range of Positive and Negative Feedback

As compared to negative feedback, positive feedback has a wider range as the process rate could get exponentially multiplied. Similarly, the range is reflected when positive feedback results to more products such as more hormones, platelets, and the like. On the contrary, negative feedback leads to less products.

  1. Vicious Cycle in Positive and Negative Feedback

Since positive feedback amplifies the disturbance, it is related with vicious cycles which could even lead to death. For instance, a positive feedback loop occurs during fever which continually fires up metabolic changes. A vicious cycle is also observed when an inflammation leads to more damage which likewise causes inflammation. However, negative feedback is most often associated with maintaining good health by restoring homeostasis.

  1. External Interruption in Positive and Negative Feedback

A positive feedback often requires an external interruption for its mechanism to stop whereas a negative feedback merely stops on its own when the original state is actualized.  For example, numerous positive feedback mechanisms occur during a progressive circulatory shock. This is characterized by declining blood pressure that can lead to heart failure. In this case, medical intervention is needed for the positive feedback to stop.

Positive Feedback vs Negative Feedback: Comparison chart

Summary of Positive vs Negative Feedback

  • Positive and negative feedbacks are control systems that help regulate process rates and homeostasis in the body.
  • Both feedbacks are important for an organism to regulate its internal processes.
  • In positive feedback, there is a direct positive correlation between the concentration and the process rate.
  • Negative feedback controls the process rate to prevent substance accumulation.
  • As compared to negative feedback, positive feedback is less frequent, stable, and intuitive.
  • Negative feedback resists change but positive feedback enhances it.
  • Generally, positive feedback has a wider range than negative feedback.
  • Positive feedback may be associated with vicious cycles and illnesses while negative feedback is closely related with maintaining good health.
  • Unlike negative feedback, positive feedback may require external interruption.

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References :


[0]Abdel-Sater, Khaled A. “Physiological Positive Feedback Mechanisms”. American Journal of Bio medical Sciences.  3.2(2011): 145-155. NWPII. Web. 28 April 2018. 

[1]Marieb, Elaine and Hoehn, Katja. Human Anatomy and Physiology. New York: Pearson, 2012. Print. 

[2]Paradise, Christopher and Campbell, Malcolm. Original Homeostasis. New York: Momentum Press, 2016. Print.

[3]Image credit: https://upload.wikimedia.org/wikipedia/commons/2/22/105_Negative_Feedback_Loops.jpg

[4]Image credit: https://upload.wikimedia.org/wikipedia/commons/thumb/a/a9/PositiveFeedbackVicious.png/549px-PositiveFeedbackVicious.png

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