Feedback mechanism

Feedback mechanism
n., plural: feedback mechanisms
[ˈfiːdˌbæk ˈmɛkəˌnɪzəm]
Definition: a loop system wherein the system responds to a perturbation

Feedback Mechanism Definition

What is a feedback mechanism? A feedback mechanism is a physiological regulation system in a living body that works to return the body to its normal internal state, or commonly known as homeostasis. In nature, feedback mechanisms can be found in a variety of environments and animal types. In a living system, the feedback mechanism takes the shape of a loop, which aids in maintaining homeostasis.

The feedback mechanism is triggered when the system undergoes a change that causes an output. The biochemical control system in living beings is made up of a variety of components, including chemicals, genes, and their regulatory connections.

When the activation of one component leads to the activation of another, the interaction between the components is said to be positive. If the activation of one component results in the inactivation of another, it is labeled as negative.

The term “feedback mechanism” was first used in cybernetics to characterize a control system’s ability to change its output in response to an input.

There are two types of feedback mechanisms; these are positive and negative feedback mechanisms.

Open and Closed-Loop Feedback Mechanisms

Homeostasis is often achieved in the body through the use of feedback loops that regulate the body’s internal circumstances. A feedback loop is a system that uses an identified receptor (sensor), the control center (integrator or comparator), effectors, and communication means to control the level of a variable.

Communication methods between the components of a feedback loop are required for it to function. This is usually accomplished through nerves or hormones, but in some circumstances, receptors and control centers are the same structures; therefore, these signaling mechanisms are not required in that phase of the loop.

The three common components of a feedback loop are the receptor (sensor), the control center (integrator or comparator), and effectors. A sensor, or commonly known as a receptor, detects and transmits a physiological value to the control center. The value is compared to the typical range by the control center. If the value deviates significantly from the setpoint, the control system stimulates an effector. A change is caused by an effector, which causes the situation to be reversed and the value to return to its normal range.

Feedback loops are commonly divided into two main types; opened-loop mechanism and closed-loop mechanism.

1. Positive feedback loops occur when a change in one direction is followed by another change in the same direction. A sensor, or commonly known as a receptor, detects and transmits a physiological value to the control center. Positive feedback loop examples can result in uncontrolled conditions since a change in an input generates reactions that cause further modifications in the same manner. Even if the components of a loop (receptor, control center, and effector) are not immediately recognizable, the term “positive feedback” is widely accepted when a variable has the ability to increase itself. Positive feedback is often damaging, however, there are a few occasions where it can help people function normally when used in moderation.

2. Negative feedback loops occur when a change in one direction produces a change in the other. For instance, a rise in a substance’s concentrations produces feedback, which causes the substance’s content to reduce. Negative feedback loops are mechanisms that seem to be naturally stable. When combined with the many stimuli that can affect a variable, negative feedback loops usually result in the value oscillating about the set point. Negative feedback loop examples include temperature and blood glucose level regulation.

READ: Sugar Homeostasis – Biology Tutorial

Feedback Mechanism Types

There are two types of feedback mechanisms, depending on whether the input changes or the physiological parameters deviate from their limits. Although the reactions of various processes to changes in variables varied, the loop’s components are similar.

I. Positive feedback mechanism

A positive feedback mechanism involves more stimulation or the acceleration of the process. Let’s find more about it below.

Positive feedback mechanism definition

What is a positive feedback mechanism? As the name implies, a positive feedback mechanism or positive feedback homeostasis is a pathway that, in response to an output variation, causes the output to vary even more in the direction of the initial deviation. A positive feedback system amplifies deviations and causes output state changes. Because it moves the body away from homeostasis, positive feedback mechanisms are significantly less common than negative feedback mechanisms. As long as the stimulus (example: the presence of the stimulant) is maintained, the positive feedback system gradually increases the reaction. A single component that activates its own activity or numerous components with direct and indirect interactions might make up a positive feedback loop. Positive feedback loops in biological processes are common in processes that need to happen fast and efficiently, as the output tends to magnify the stimulus’ influence. Positive mechanisms are rare in living systems such as the human body, but they can be found in the environment, such as in the instance of fruit ripening.

Steps / Process / Mechanism of positive feedback mechanism

The process of a positive feedback loop consists of a control system that consists of various components, working in a circular pathway to stimulate or inhibit one another. The overall process can be described in terms of the components of the system.

1. Stimulation. The stimulation that initiates the positive feedback loop in order to complete a process is the initial step. Hormones released by various organs as a result of the start of a process are the most common stimuli in the human body.
2. Reception. The second step in the loop is the reception of stimuli via various sensors, which provide data to the control unit. These receptors are mostly nerves that transmit signals from the stimulus location to the control unit, which is the brain in humans.
3. Processing. The processing of information supplied to the control unit by the receptors is the next phase in the loop. The control unit tallies the data and displays an output if the stimulus is outside the typical range of the value.
4. Stimuli are activated even more. In order to induce an output in response to the stimulus, information from the brain is conveyed to the location of action via several nerves. The brain’s messages tend to activate the stimulus even more in the direction of deviation in the case of a positive feedback loop.

Positive feedback mechanism examples

• Blood Clotting

When a wound creates bleeding, the body responds by clotting the blood and preventing blood loss through a positive feedback loop. The wounded blood vessel wall releases substances that start the clotting process. Platelets in the blood begin to adhere to the wounded area and produce substances that attract more platelets. As the platelets continue to accumulate, more chemicals are released, and more platelets are drawn to the clot location. The clotting process is accelerated by the positive feedback until the clot is large enough to halt the bleeding.

• Childbirth

In humans, a positive feedback mechanism is noticed during childbirth, which is caused by the baby pressing against the ovary wall. The brain receives the pushing feeling via several nerves, and the pituitary is stimulated to generate oxytocin in response. The oxytocin feedback loop is responsible for uterine muscle contractions, which cause the fetus to come closer to the cervix, thereby increasing the stimulation. Until the baby is born, the positive feedback loop continues.

The positive feedback loop that regulates childbirth is seen in the diagram above. When the infant’s head bumps up against the cervix, the procedure usually starts. Nerve impulses flow from the cervix to the hypothalamus in the brain as a result of this stimulation. The hypothalamus responds by sending the hormone oxytocin to the pituitary gland, which secretes it into the bloodstream to reach the uterus. Oxytocin causes uterine contractions to increase, pushing the baby closer to the cervix. As a result, the cervix begins to dilate in preparation for the baby’s passage. Increased levels of oxytocin, stronger uterine contractions, and wider cervix dilatation continue this cycle of positive feedback until the baby is pushed through the delivery canal and out of the body. The cervix is no longer stimulated to send nerve impulses to the brain at this stage, and the entire process comes to a halt.

• Menstrual cycle

The hormone estrogen is released by the ovaries at the start of the menstrual cycle. The estrogen operates as a positive feedback loop stimulation. The information is delivered to the brain, which prompts the hypothalamus to release gonadotrophin-releasing hormone and the pituitary to release luteinizing hormone. The control unit releases these hormones in response to the stimulation. These hormones then cause the ovaries to release estrogen, and the cycle repeats itself until the levels of these hormones are high enough to trigger the release of follicle-stimulating hormone. After the release of follicle-stimulating hormone, ovulation occurs, and the menstrual cycle begins. The rise in one element causes the output to move in the same direction until the task is done, which is an example of a positive feedback process.

• Fruit Ripening

A tree or bush will suddenly ripen all of its fruit or vegetables without any visible warning, which is a startling event in nature. This is the first time a positive biological feedback loop has been observed in action. In the flash of an eye, an apple tree with many apples appears to go from unripe to ripe to overripe. This will start with the very first ripe apple. When fully ripe, it emits the gas ethylene (C2H4) via its skin. When apples are exposed to this gas, they ripen as well. They, too, generate ethylene once ripe, which continues to ripen the rest of the tree in a wave-like action. This feedback loop is commonly utilized in the fruit industry, with apples being exposed to ethylene gas to increase ripening.

II. Negative feedback mechanism

Let’s take a look now at the negative feedback mechanism, particularly its steps (mechanisms) and examples.

Negative feedback mechanism definition

What is a negative feedback mechanism? A negative feedback mechanism, often known as negative feedback homeostasis, is a pathway that is triggered by a deviation in output and produces changes in output in the opposite direction of the initial deviation. After the control unit analyzes the magnitude of the deviation, the negative feedback mechanism drives the variable factors towards a stable state or homeostasis. Positive feedback loops are less prevalent than negative feedback loops because negative feedback loops tend to stabilize the system.

Steps in a negative feedback mechanism

The negative feedback system works in a similar way to the positive feedback loop in that it is activated by stimuli and eventually leads to modifications that tend to cancel out those impulses. The following is a summary of the overall procedure:

1. Stimulation. The development of stimuli as a result of physiological parameter deviations from the normal value is the initial stage in the negative feedback loop. Physiological parameters can deviate from the norm in either direction.
2. Reception. The control unit receives changes in physiological parameters through a variety of receptors located throughout the body. Nerves and other thermoreceptors are examples of common receptors engaged in stimulus transmission.
3. Processing. The brain serves as the loop’s control unit, determining whether a change in a physiological parameter necessitates loop activation or inhibition. The brain sends out signals to erase the alterations in different ways depending on the direction of departure.
4. Counteract on the stimulus. The control unit sends out signals at the end of the loop to cancel out the impacts that cause changes in physiological variables. Changes can take several forms and be directed at different sections of the body.

Examples of negative feedback

• Regulating Temperature

A typical example of a negative feedback mechanism in the human body is the regulation of body temperature via endotherms. When the body’s temperature rises above normal, the brain sends signals to various organs, including the skin, to release heat in the form of sweat. These physiological actions cause the temperature to drop to the point where the negative feedback mechanism’s pathways are shut down. When the body temperature rises above its typical level in order to preserve homeostasis, a similar mechanism happens.

• Regulating Blood Glucose Level

A negative feedback mechanism regulates the concentration of glucose in the blood. More glucose is absorbed in the gut and stored in the form of glycogen in the liver when blood glucose levels rise above the usual range. Insulin secretion from the pancreas is in charge of conversion and conservation. Insulin encourages glucose absorption in the muscles and liver. When blood glucose levels drop and more glucose is needed in the blood, insulin release is suppressed, which reduces blood glucose absorption.

Positive vs. Negative Feedback Mechanism

Here is a summary of the differences between a positive feedback mechanism and a negative feedback mechanism.

Try to answer the quiz below to check what you have learned so far about the feedback mechanisms.

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References

• Biga, L.,Dawson, S.,Harwell A.,Hopkins, R.,Kaufmann J.,LeMaster, M.,Matern, P.,Graham K., Quick, D. and Runyeon, J. (2021). Anatomy and Physiology. Retrieved from https://open.oregonstate.education/aandp/chapter/1-3-homeostasis/
• Lumen Learning. (2019). Homeostasis from Boundless Anatomy and Physiology. Retrieved from https://courses.lumenlearning.com/boundless-ap/chapter/homeostasis/
• Kahn Academy (2019) Homeostasis. In Human Body Systems. Retrieved from https://www.khanacademy.org/science/high-school-biology/hs-human-body-systems/hs-body-structure-and-homeostasis/a/homeostasis
• Torday, J. S. (2021). “Homeostasis as the Mechanism of Evolution.” Biology vol. 4,3 573-90.  doi:10.3390/biology4030573
• Wakim, S. and Grewal, M. (2021). Homeostasis and Feedback. Retrieved from https://bio.libretexts.org/Bookshelves/Human_Biology/Book%3A_Human_Biology_(Wakim_and_Grewal)/10%3A_Introduction_to_the_Human_Body/10.7%3A_Homeostasis_and_Feedback

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