Feedback Mechanism Definition

• The feedback mechanism is the bodily regulatory system that helps maintain homeostasis, or the natural interior state of the body.
• These processes may be observed in a variety of natural environments and animal species.
• The feedback mechanism in a biological system adopts the form of a loop, which aids in maintaining homeostasis.
• The system alteration that produces an output triggers the feedback process.
• Molecules, genes, and the regulatory interactions between these components make up the biochemical control system in living things.
• When the activation of one component leads to the stimulation of the other, the relationship between the elements is deemed positive. Negative components are those in which the stimulation of one component leads to the inactivation of another.
• Cybernetics was the first discipline to adopt the word “feedback mechanism” to describe a control system’s ability to modify its output in accordance with input.
• Among living systems, feedback mechanisms, also referred to as feedback loops, assist the body in maintaining homeostasis by amplifying or inhibiting a certain biological pathway or activity.
• Bringing the status of the body into a stable condition is the primary goal of the feedback mechanism in every system.
• The feedback system consists of three distinct components: the control centre, detector, and effector. 
• The control centre serves as the “brain” of the system, determining the ranges in which the variable factors should fall.
• In order to transfer the data to the control centre, the detector or sensor must first accept the input and integrate the incoming data.
• The control centre decides if an adjustment is required based on the received signals and delivers the signal to the effector accordingly.
• After receiving the output, the effector modifies the variable factor to maintain it within its allowed range.
• The feedback mechanism is a dynamic process that modifies a variety of physiological properties throughout time.

Feedback mechanism types

Based on the modification in input or the departure of physiological parameters from their limits, there are two different types of feedback processes. The elements of the loop are identical even though the responses of these processes to changes in variables vary.

Positive Feedback Mechanism Loop

Definition of a Positive Feedback Mechanism

• As the name implies, a positive feedback mechanism describes a process which, in response to an output deviation, induces the output to deviate in the opposite direction.
• A mechanism that produces positive feedback increases deviations and induces changes in the output state.
• Because it pulls the body out of equilibrium, positive feedback systems are far less common than their negative counterparts.
• Positive feedback steadily strengthens the reaction as long as the trigger is present.
• The positive feedback loop may consist of a single unit that initiates its own action or many elements that interact directly or indirectly.
• Positive feedback loops are frequently seen in biological processes that must move fast and toward completion since the output tends to magnify the stimulus’s influence.
• Although there aren’t many positive processes in living systems like the human body, there are several that may be seen in the environment, as when fruit ripens.

Steps/Process/Mechanism of the Positive Feedback Mechanism

A control system made up of multiple parts that operate in a circular pattern to either stimulate or inhibit one another constitutes a positive feedback loop. The system’s parts can be used to define the whole procedure.

1. Stimulation

• The stimulus that initiates the loop in order to finish a process is the first step in the positive feedback loop.
• The bulk of triggers in the human organs are hormones generated by diverse organs in response to the initiation of a process.
• The contraction experienced during labour is an illustration of a stimulus that starts a positive feedback process.

2. Reception

• Receiving inputs through various sensors and transmitting that information to the control unit is the second phase of the loop.
• The majority of these receptors are nerves that transmit signals from the stimulus location to the managing unit, which is the brain in humans.

3. Processing

• Processing the data that the receptors deliver to the control unit is the following phase in the loop.
• The control unit totals the data to determine whether the stimulus is beyond the expected range of the value before displaying an output.
• When a woman is giving birth, the brain learns about the uterine wall contractions and prompts the pituitary gland to release the hormone oxytocin.

Further activation of the stimuli

• To produce an output in response to the stimuli, the brain’s information is transmitted to the location of activity via several nerves.
• When there is a positive feedback loop, the brain’s messages have a tendency to make the stimulus more active in the offending direction.
• The stimulation of the pituitary gland to create oxytocin, which further enhances the muscular contractions of the uterine wall in delivery, is one example of this mechanism.

Examples of Positive Feedback Mechanisms

1. Menstrual cycle

• At the onset of the menstrual cycle, the ovaries secrete the hormone oestrogen. Oestrogen is what stimulates the positive feedback loop.
• The signal is transmitted to the brain, which in turn triggers the production of luteinizing hormone from the pituitary and gonadotrophin-releasing hormone from the hypothalamus.
• These hormones are released by the control unit in response to stimulus. The cycle repeats until the concentrations of these hormones are sufficient to stimulate the synthesis of follicle-stimulating hormone. These hormones further promote the release of oestrogen by the ovaries.
• Once ovulation occurs as a result of follicle-stimulating hormone production, the menstrual cycle will ultimately start.
• Because the output travels in the same direction as it does while one element is raised, this serves as an example of a positive feedback system.

2. Childbirth

• A similar positive feedback loop is observed in humans during childbirth while the baby pushes on the ovary wall.
• Multiple nerves transmit the pressing feeling to the brain, which then prompts the pituitary to release oxytocin in response.
• The uterine muscles’ contractions, which result in the foetus moving toward the cervix and amplifying the stimulation, are brought on by oxytocin.
• Until the baby is delivered, the positive feedback loop remains in place.

Negative Feedback Mechanism Loop

Definition of Negative Feedback Mechanism

• A route that is sparked by an output deviation and that results in changes in output that are in the direction opposite to the original deviation is known as a negative feedback mechanism or loop.
• The variable components are driven toward a stable state or homeostasis by the negative feedback mechanism after the control unit has grasped the extent of the divergence.
• Because negative feedback loops work to stabilise the system, positive feedback loops are more uncommon than negative ones.
• Once the output changes, the loop reacts in the opposite way to cancel out the stimulus that caused it.
• These loops are initiated in two situations: when the variable’s value must be increased because it is below its normal range, and when it is above the normal values and needs to be brought down.
• As a component of homeostasis, negative feedback processes take place to counteract the stimulus that initially caused the deviation in order to return the variables to their normal values.
• Similar to a positive feedback mechanism, a negative feedback mechanism has many parts that work together to keep the system in a stable condition.

Steps / Process / Mechanism of Negative Feedback Mechanism

The negative feedback mechanism, like the positive feedback loop, is triggered by stimuli and subsequently leads to alterations that essentially cancel out those impulses.

The general procedure may be summarised as follows:

1. Stimulation

• The negative feedback loop is started when a physiological parameter deviates from its usual value and produces stimuli as a result. For physiological parameter variation, both extremes are possible.
• Many physiological processes may need to be either activated or inhibited to restore the body to its normal state after the deviation.
• The most prevalent and simple to comprehend stimulus is a shift in body temperature outside of the typical range.

2. Reception

• The control unit receives the changes in the physiological parameters through various sensors located in various body regions.
• Nerves and other thermoreceptors are a handful of the widespread receptors engaged in the stimulation’s transmission.

3. Processing

• The brain serves as the loop’s control unit, and it first decides whether a change in a physiological parameter calls for activating or inhibiting the loop.
• The brain sends messages to various systems to reverse the alterations based on the direction of deviation.
• The set of cells in the brain’s hypothalamus function as the control system for variations in body temperature.

4. Counteract on the stimulus

• The control unit sends out signals to cancel out the impacts that are changing the physiological parameters in the last phase of the loop.
• Different sorts of alterations can be made, and they can target various bodily sections. The nervous system transmits information to many organs.
• The hypothalamus transmits signals that cause shivering, blood vessel constriction, and behavioural changes like curling up as the body temperature drops.
• These actions raise body temperature. This blocks the feedback loop, stopping the cycle until the body temperature falls again.

Examples of Negative Feedback Mechanisms

1. Regulation of blood glucose levels

• Negative feedback is the process that regulates blood glucose levels.
• In the intestines, much glucose is ingested, and the liver stores it as glycogen if the blood glucose level rises above the usual range.
• Insulin released by the pancreas regulates conversion and conservation. The hormone insulin encourages the liver and muscles to absorb glucose.
• The release of insulin is blocked when blood glucose levels drop and more glucose is needed in the circulation, which lowers blood glucose absorption.

2. Temperature regulation

• Another well-known example of a negative feedback system in the human body is endotherms, which control body temperature.
• While the body temperature goes above normal, the brain transmits signals to numerous physical organs, such as the skin, to emit heat in the form of sweat.
• These physiological processes finally cause the temperature to decrease to a level where the channels of the negative feedback system are made to shut down.
• A similar procedure takes place if the body temperature rises over the usual range in order to preserve homeostasis.

Applications of the Feedback mechanism

Applications for feedback mechanisms may be found in a variety of systems and fields.

1. In biology, feedback mechanisms play a role in preserving homeostasis in both individual organisms and whole ecosystems. Both positive and negative feedback mechanisms are involved in homeostasis, but the latter is more common.
2. The feedback mechanism is utilised in mathematics and dynamic systems to alter the behaviour of diverse systems in accordance with the requirements of the application.
3. Positive and negative feedback processes have been used in a variety of climate science research to track the impact on the atmosphere, ocean, and land.
4. The mechanism is employed in electronic engineering components, including amplifiers, oscillators, and logic circuits, where it is most frequently used.

References

• Waugh A and Grant A. (2004) Anatomy and Physiology. Ninth Edition. Churchill Livingstone.
• Mitrophanov, Alexander Y, and Eduardo A Groisman. “Positive feedback in cellular control systems.” BioEssays: news and reviews in molecular, cellular and developmental biology vol. 30,6 (2008): 542-55. doi:10.1002/bies.20769
• Fagerlund, Riku et al. “Anatomy of a negative feedback loop: the case of IκBα.” Journal of the Royal Society, Interface vol. 12,110 (2015): 0262. doi:10.1098/rsif.2015.0262
• Libretti S, Puckett Y. Physiology, Homeostasis. [Updated 2020 Jun 21]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK559138/
• Torday, John S. “Homeostasis as the Mechanism of Evolution.” Biology vol. 4,3 573-90. 15 Sep. 2015, doi:10.3390/biology4030573
• APPLICATIONS OF FEEDBACK SYSTEMS. In The Commonwealth and International Library: Applied Electricity and Electronics Division. Electronic Engineering Applications of Two-Port Networks. Pergamon. 1976. Pages 171-207. https://doi.org/10.1016/B978-0-08-018069-4.50015-1.
• Lehrer, Paul, and David Eddie. “Dynamic processes in regulation and some implications for biofeedback and biobehavioral interventions.” Applied psychophysiology and biofeedback vol. 38,2 (2013): 143-55. doi:10.1007/s10484-013-9217-6
• Liu, Wang et al. “Application of Feedback System Control Optimization Technique in Combined Use of Dual Antiplatelet Therapy and Herbal Medicines.” Frontiers in physiology vol. 9 491. 4 May. 2018, doi:10.3389/fphys.2018.00491
• Rahman, Anisur et al. “Importance of Feedback and Feedforward Loops to Adaptive Immune Response Modeling.” CPT: pharmacometrics & systems pharmacology vol. 7,10 (2018): 621-628. doi:10.1002/psp4.12352

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