Difference Between Positive and Negative Feedback Loops

Positive vs Negative Feedback Loops

Positive and negative feedback loops are controlled by organized feedback mechanisms which are involved in maintaining a state of homeostasis of vertebrates. Homeostasis is known as the dynamic constancy of the internal environment of an animal. There are two basic mechanisms that are involved in maintaining the dynamic constancy; they are Negative feedback mechanism and Positive feedback mechanism. Here, if conditions deviate from a defined value or a set point, biochemical reactions are initiated to get the conditions back toward the set point.

What is Positive Feedback Loop?

Positive feedback loops are involved in very few cases, in vertebrate body. They basically accentuate a change, which eventually drives the value of the controlled variable even further from the set point. As a result, positive feedback sometimes results in highly unstable system, in the body. Though these systems are unstable, they can be important components of some physiological mechanisms. For example, positive feedback loops play a major role in blood clotting and contraction of the uterus during childbirth. In the case of blood clotting, one clotting factor activates another in a cascade which ultimately accelerates the formation of clot whereas, in the uterus contractions, each contraction stimulates further stretching, hence enhance the contractions and stretching of uterus until it expels the fetus during the childbirth.

What is Negative Feedback Loop?

Negative feedback loops mainly keep internal variables within a range in order to maintain homeostasis. In negative feedback loop, special sensors are involved to detect the changes and conditions within the body as well as outside it. Sensors can be specialized cells or membrane receptors. Negative feedback mechanisms are involved to control body temperature, blood glucose concentration, electrolyte (ion) concentration, tension on a tendon etc. When a deviation of a variable exists, integration center initiates a signal, which in turn increases or decreases the activity of a particular target to get the variable back to the set point. Effectors involved in negative feedback mechanism are usually muscles or glands and integration center is often a particular region of the brain or spinal cord.

What are the differences between Positive and Negative Feedback Loops?

• Negative feedback loop is used more commonly than positive feedback loop. 

• Negative feedback loops are involved to correct deviations of temperature, pH and many more internal variables, whereas positive feedback loops are involved to maintain specialized changes.

• Negative feedback loops involve in maintaining body temperature, pH, ion concentration etc., whereas positive feedback loops involve in blood clotting and uterus contractions, in childbirth.

• Negative feedback loops always help to maintain homeostasis, whereas positive feedback usually destabilizes the systems in the body; hence do not help to maintain homeostasis more often.