Positive Feedback: Definition, Mechanism, and Examples (2023)

To work effectively, each bodily mechanism, such as temperature, blood pressure, and quantities of particular nutrients, must be in the optimum range. A normal value around which the standard range fluctuates is called an optimal value. The body remains healthy and stable when the standard or optimal range is maintained. Various biological systems act on the body’s input and output as a result of certain stimuli.

In order to maintain homeostasis, feedback loops are critical. Homeostasis is the protection of the body’s internal environment from the effects and fluctuations of the external environment, and it aids in body stability.

Homeostasis is determined by two key factors:

1. Organismal classification

2. The organism’s habitat

A cold-blooded species, such as a fish, maintains a lower body temperature in response to its surroundings, whereas a warm-blooded animal, such as a whale, maintains a greater body temperature to maintain internal stability. A favourable response or a self-reinforcing response to external or internal stimuli is known as positive feedback. In this case, the effector increases the stimulus, which improves product creation and maintains body stability. Instead of correcting a physiological change, positive feedback encourages it.

A physiological system that supports the change is called positive feedback (works to reinforce or intensify the change). The receptor detects the variation, and the effector then tries to create the same result, enhancing the physiological change. The positive feedback loop will continue to increase the real change until the stimulus is eliminated.

Consider the following scenarios: clot formation, delivery, fruit ripening, and the menstrual cycle. Each one shows the operation of a positive feedback mechanism:

• To seal a wound, clotting factors are released.

• When a baby is born, the uterus’s walls dilate, causing a contraction that stimulates the uterus to stretch even more (this continues until birth).

• When fruits ripen, ethylene is released, which helps to keep the ripening process going.

• The oestrogen hormone stimulates the release of other hormones that lead to ovulation throughout the menstrual cycle.

1. The Ferguson reflex is the start of contractions during delivery.

2. In the case of childbirth, the uterine walls ultimately expand due to the baby’s development, which is represented by the stretch receptors.

3. This stretching will promote the release of oxytocin hormones, which will engage the uterine muscles and reduce the uterine gap.

4. It causes the uterus to expand more, resulting in additional contractions until the initial trigger (the foetus) is gone (i.e., birth).

Homeostasis is achieved by the interaction of four fundamental components.

1. Stimulus

2. Sensor (Receptor)

3. Control Centre

4. Effector

The control centre is a component of the feedback system that compares the magnitude of variation to the average value. Not only does it receive signals from sensors, but it also analyses them. The brain’s control centre notices the alterations and compares them to normal levels. If the value is not within the optimal range, the control centre sends an instantaneous signal to the effector to preserve bodily balance.

The pituitary gland is positioned near the brain, which is the command centre for a variety of responses. In reaction to the stimulation, it releases hormones such as oxytocin, antidiuretic hormone, and growth hormone.

The effector can be any muscle, organ, gland, or other tissue that responds to the stimuli in accordance with the control centre’s signal. The stimulus is either opposed or enhanced by the effector. The effector’s reaction is determined by the command received by a control centre. The effector’s objective is to keep the variable close to the standard point in order to preserve stability.

The contraction of the uterus, for example, is the outcome of positive feedback in labour. The uterus is the effector organ in this case.

Feedback loops are biological processes that aid in the body’s maintenance of homeostasis. This happens when a product or event occurs that changes the body’s reaction.

A positive feedback loop keeps the stimulus in the same direction and presumably speeds up the action. An explosion of chemical events that lead to blood clotting, also known as coagulation, is an example of positive feedback loops seen in the animal body. As one clotting factor activates, it will prompt the activation of others in a chain reaction until a clot, fibrin, is produced. This method maintains the event’s course rather than changing it, thus it has positive feedback.

Positive feedback includes contractions during delivery and fruit ripening. The transformation is slowed by a negative feedback loop. To return the system to a stable condition, the response impact is reduced.

Negative feedback occurs when a change or output is minimised. To return the system to an even and stable state, the response’s influence is decreased. In every homeostatic process, changing the direction of the stimulus creates a negative feedback loop. Negative feedback alters the stimulus’s magnitude but does not allow it to continue its action. In other words, when the levels are high, the body exerts effort to reduce them, and when the levels are low, the body exerts effort to raise them.

Regulating blood glucose levels and osmoregulation are two examples of negative feedback. Thermoregulation is another. When the body temperature deviates from its usual range, the system kicks in to bring it back to normal. In homeostatic physiological processes, the negative reaction happens more frequently than the positive response. A disruption in the natural bodily system is the root of many diseases. As productivity rises, so does the amount of action in positive feedback. As a result, the reaction impact is magnified in the end.

Bad feedback, on the other hand, slows down the rate at which a condition develops, which can have either positive or negative repercussions. As a result, the reaction response is stifled.

Negative feedback, as opposed to positive feedback, is closely linked to stability since it reduces the impact of stimuli. Positive responses, on the other hand, lead to production, which might lead to unpredictability. Negative feedback demonstrates resistance to changes by working to restore the body’s system to its original condition and reverse the change. Positive feedback, on the other hand, tends to encourage transformation and change.

External intervention is usually required to stop a good reaction from working. When the body is under circulatory shock, for example, it receives positive feedback in order to deal with the situation. The blood pressure continues to decrease in this situation, which might lead to heart failure. To halt positive feedback in such instances, medical therapy is necessary. Negative feedback, on the other hand, is completely self-contained. It will come to an end once stability has been attained.

The internal mechanism of the body cannot establish equilibrium if it is deprived of feedback. It indicates that the body’s ability to manage its systems is deteriorating. While negative input is frequent in sustaining stability, good feedback is equally important.

Hormonal response pattern: hormone concentration in plasma is influenced by factors such as secretion rate and serum hormone concentration.

Corticotropin hormone is secreted by the hypothalamus, which stimulates the pituitary gland to release adrenocorticotropic hormone (ACTH). The adrenal gland is stimulated to produce cortisol by ACTH. When ACTH levels in the blood begin to rise, the hypothalamus receives a signal to halt CRH production. Cortisol also “returns” to the pituitary gland and brain when plasma levels rise, preventing the production of adrenocorticotropic and corticotropin hormones, respectively. As a result, a small change in the defined region triggers a corrective action on the opposite side. Negative feedback helps to avoid excessive hormone release in this way.

Because of breast sucking, there is a neural reaction in the spinal cord during lactation. The pituitary gland is stimulated as a result of this reaction ascending to the hypothalamus. As a result, more prolactin is generated, which encourages the production of milk.

Another significant aspect of positive feedback is that it causes ovulation by increasing oestrogen levels throughout the menstrual cycle phase. Positive reactions are also influenced by the generation of sensory nerve impulses, which is an essential physiologic component.

The membrane produces a modest leak of sodium ions through sodium channels in the nerve fibre. This causes a shift in membrane potential, which in turn causes numerous sodium channels to activate (Hodgkin cycle). The first tiny leak triggers a cascade of sodium leaks, which are necessary for the propagation of the nerve action potential.

Positive feedback is also useful for sustaining other cell signalling systems, such as enzyme kinetics and physiological mechanisms. Positive feedback can be utilised to boost B cell activity. When a B cell’s antibodies attach to an antigen, it triggers an immunological response in which additional antibodies are generated and released.

Apoptosis is a type of planned cell death that attempts to rid the body of damaged and undesirable cells. If this mechanism does not function properly, severe repercussions, such as cancer, will result. The auto-activation of caspases lies at the heart of this process, which may be followed by a positive feedback loop.

Positive feedback is a type of feedback that reacts to a disturbance in the same way as the perturbation does. It has a tendency to start or speed up a biological process. The perturbation signal is magnified in this system, and the output might rise exponentially or even hyperbolically. The beginning of contractions during delivery is an example of biological positive feedback.

When a contraction occurs, the hormone oxytocin is released into the body, which causes the body to contract even more. As a result, the amplitude and frequency of contractions increase. Another example occurs during the coagulation of blood. Signal molecules are produced when a tissue is damaged. These chemicals cause circulating platelets to release additional chemicals, causing more platelets to be activated, which is necessary for the development of a blood clot. Nerve signal production and gene regulation are two more instances of positive feedback.

Zygote: Definition, Stages, and Diagram

• Positive feedback in cellular control systems. Bioessays . 2008 Jun;30(6):542-55.
• A model for positive feedback control of the transformation of fibroblasts to myofibroblasts. Prog Biophys Mol Biol . 2019 Jul;144:30-40.
• Autoactivation of small GTPases by the GEF-effector positive feedback modules. F1000Res . 2019 Sep 23;8:F1000 Faculty Rev-1676.
• Positive Feedback Loops in Alzheimer’s Disease: The Alzheimer’s Feedback Hypothesis. J Alzheimers Dis . 2018;66(1):25-36.