Biological Sciences
Negative Feedback
Negative feedback is a regulatory mechanism in biological systems that helps maintain stability and homeostasis. It involves the response to a change in a system that counteracts the initial change, effectively dampening or reducing the magnitude of the change. This process helps to keep physiological variables within a normal range and prevent excessive fluctuations.
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8 Key excerpts on "Negative Feedback"
eBook - PDF- Jonathan Bubb(Author)
- 2021(Publication Date)
- Cengage Learning EMEA(Publisher)
Once we respond to a change in our environ- ment, we have to ensure that we can turn off this response. Therefore, our body has a built-in mechanism known as Negative Feedback. Negative Feedback occurs when the product of a stimulus leads to the decrease or inhibition of the original stimulus that caused it. As a result, the original stimulus in Negative Feedback loops leads to the creation of its own inhibitor (Figure 7-6). THERMOREGULATION Thermoregulation is a classic example of how Negative Feedback mechanisms work to inhibit the original stimulus. Copyright 2021 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Chapter 7 The Endocrine System 435 When body temperature levels rise above 37°C (98.6°F) due to exercise, fever, or hot climates, the hypothalamus becomes activated. Through a series of upregu- lation of specific hormones (discussed later), the hypothalamic regulatory cen- ters can cause sweat glands to begin to secrete perspiration onto the surface of the skin. This will begin to cool the body and release heat. A reduction in body temperature and return to the normal 37°C benchmark will effectively shut off the hypothalamic regulatory center. Think of the body as a giant thermostat in a home heating system. Sensors in the thermostat can detect temperature changes in the home. If the temperature drops below the set point that you have entered into the thermostat, the heating system is activated. Hot air begins to enter the room until the temperature in the room has reached the set point you determined.
eBook - PDF- George Spilich(Author)
- 2023(Publication Date)
- Wiley(Publisher)
Negative Feedback systems occur throughout our everyday life, and you can practice identifying them in this Try It Out: Negative Feedback Systems in Nature and Technology. Effector: The compressor and fan in the AC unit run until the room has cooled to the set point. Sensor: The thermocouple in the thermostat is constantly monitoring the room temperature. Return to set point Control: When the sensor indicates that the temperature has exceeded the set point, the air conditioning switches on. 68°F The room temperature exceeds the set point. Stimulus: FIGURE 7.2 A Negative Feedback system When the sensor detects that the system is out of equilibrium, it activates a control system that engages the effector to bring the system back into balance. When the sensor detects that the system is back in balance, it signals the control system to deactivate the effector. Try It Out Negative Feedback Systems in Nature and Technology As you learn how the brain and body work together, you see time and again that Negative Feedback loops are an efficient mechanism for maintaining equilibrium. A regulatory system that is dormant unless some aspect veers out of limits is so useful that we see them in many situations. Download the worksheet Negative Feedback Systems in Nature and Technol- ogy and explain how a Negative Feedback loop functions to maintain an equilibrium in each situation. AlexMax/Getty Images 178 C H A P T E R 7 Homeostatic Regulation of the Internal Environment 7.1 Before You Go On Section Summary Our nervous system works to maintains homeostatic levels of basic functions such as temperature, fluids, and calories. It does so through Negative Feedback systems that sense when a system deviates suffi- ciently from the set point and then returns the system to homeostasis or equilibrium. Comprehension Check 1. Which is the best definition of homeostasis? a. maintaining a positive attitude b. breathing in oxygen and releasing carbon dioxide c.
eBook - PDF- Carlo Cosentino, Declan Bates(Authors)
- 2011(Publication Date)
- CRC Press(Publisher)
4 Negative Feedback systems 4.1 Introduction Negative Feedback is a powerful mechanism for changing and controlling the dynamics of a system. Through the expert use of this type of feedback, control engineers are able to manipulate the dynamics of a huge variety of different systems, so that they behave in a way that is desirable and efficient from the point of view of the user, [1, 2, 3]. In biological systems, evolutionary pres-sures have led to the use of Negative Feedback for a wide variety of purposes, including homeostasis, chemotaxis, adaptation and signal transduction. As shown in Fig. 4.1, the principle of Negative Feedback is extremely simple: a feedback loop is closed around a system G and the measured output of the system y is compared to its desired value r . The resulting error signal e is acted on by a controller K , which generates an input signal u for the system which causes its output to move towards its desired value. Note that, depend-ing on the type of system, and the level of control required, the controller K could be as simple as a unity gain or as complex as a high-order nonlinear dynamical system. Consider, for example, a simple first-order system G ( s ) K G + -Σ r(t) u(t) y(t) e(t) FIGURE 4.1: Negative Feedback control scheme. which has a time constant of 3 seconds and a system gain of 10: Y ( s ) = G ( s ) U ( s ); G ( s ) = 10 3 s + 1 (4.1) 115 116 Feedback Control in Systems Biology The response of this system to a step input U ( s ) = 1 /s is shown in Fig. 4.2, and as expected, the system takes 3 seconds to reach 63% of its final value. Suppose the response of the system is now required to be much faster than 0 5 10 15 0 5 10 Step response of G(s) Amplitude 0 0.5 1 1.5 2 2.5 3 0 0.5 1 Closed-loop step response Amplitude Time (s) FIGURE 4.2: Step responses of G ( s ) = 10 / (3 s +1) with and without feedback control.
eBook - PDF- Bryan H. Derrickson(Author)
- 2019(Publication Date)
- Wiley(Publisher)
If dis- ruption is extreme, regulation of homeostasis may fail. 6. Most often, the nervous and endocrine systems, acting together or separately, regulate homeostasis. The nervous system detects body changes and sends action potentials to counteract the changes. The endocrine system regulates homeostasis by secreting hormones. 7. Feedback systems include three components: (1) Receptors monitor changes in a controlled variable and send input to a control center; (2) the control center determines the set point at which a controlled variable should be maintained, evaluates the input it receives from receptors, and generates output commands when they are needed; and (3) effectors receive output from the control center and produce a response (effect) that alters the controlled variable. 8. If a response reverses the original stimulus, the system is operat- ing by Negative Feedback. One example of Negative Feedback is the regulation of blood pressure. If a response enhances the original stimulus, the system is operating by positive feedback. One exam- ple of positive feedback is uterine contractions during the birth of a baby. 9. In addition to feedback systems, homeostasis may also involve feed- forward control. In feedforward control, events occur in anticipation of a change in a controlled variable. An example of feedback control occurs when the sight, smell, or thought of food causes your mouth to salivate and your stomach to produce gastric juice. 10. Disruptions of homeostasis—homeostatic imbalances—can lead to disorders, diseases, and even death. 1.5 Physiology as a Science 1. The term physiology is derived from the physiologoi, a group of ancient Greek philosophers who speculated about the existence and purpose of all things in nature. 2. Over time, the scope of physiology began to focus on how living things in nature function. Hippocrates, Aristotle, Erasistratus, and Galen (all Greek) were among the first to study body function.
eBook - PDF- Claire Leader, Ian Peate(Authors)
- 2024(Publication Date)
- Wiley-Blackwell(Publisher)
An example of this might be the regulation of blood glucose, where an increase or decrease in blood TABLE 6.1 Changes that receptors can initiate. Blood pressure Blood glucose levels Oxygen and carbon dioxide levels within tissues and blood Body fluid pH levels Concentration levels of water and electrolytes Feedback Mechanisms 107 glucose levels outside of the homeostatic range sets in motion processes that will either reduce or increase glucose levels so that blood glucose levels remain constant over time. Positive Feedback Mechanisms Positive feedback mechanisms play a much smaller role in the body’s homeostatic control and there are only a few of these ‘amplifier’ systems in the body (Waugh and Grant 2018). In positive feedback mechanisms, the disturbance is allowed to increase in its direction and resultant loss of homeostasis. While this homeostatic disturbance can be detrimental and lead to ill health, positive feedback is desirable when rapid change is required. An example of this is lactation. A suckling action of the baby at its mother’s breast leads to the production of prolactin, which leads to milk production. The more the baby suckles, the more prolactin and ultimately breast milk is produced. When the demand for breastfeeding stops, prolactin levels decrease and breast milk production stops. The body’s nervous and endocrine systems are the two main systems that are involved in the maintenance of homeostasis. While each of the body’s individual systems works independently and is to a certain degree self-regulating, they are also reliant on one another to maintain homeostasis, as a disturbance in one body system can affect the functioning of another. Therefore, there is a need for systems to interrelate and work together to maintain a constant and balanced, stable internal environment that maintains health. Table 6.2 outlines the functions that individual body systems perform that maintain homeostasis.
eBook - PDFFoundations of Mathematical Biology
Supercellular Systems
- Robert J. Rosen(Author)
- 2013(Publication Date)
- Academic Press(Publisher)
Such a deviation would typically be caused by disturbances or pathogenic factors. Homeostasis thus produces a continual readjustment of vital physiological values as a result of uninterrupted monitoring by means of sensing elements. Occasionally, it also involves resetting the physiological value, as exemplified in the change of thermoregulatory homeostasis from the normal warm-blooded mam-malian condition to the torporific condition of hibernation. Homeostatic mechanisms and physiological control systems in general can be described in terms of the typical feedback system configuration of Fig. 10. Receptors are readily recognized as elements which provide con-tinuous information about the actual state of the system and, therefore, constitute the feedback portion of the system. The comparator can usually be viewed as a center of nervous integration receiving signals from the receptors, from the integrative centers of other control systems (Fig. 1) and also from higher nervous centers. Its function may be reasonably inferred as one of comparison between a desired state of the system determined by the activity supplied by the higher centers and the actual state of the systems as described by the receptor signals. However, this idea is not necessary in practice, although it is useful conceptually. Thus, in detail the condition of zero error may in fact merely be the condition of equilibrium for the system.
eBook - PDF- Srinivas Aluru(Author)
- 2005(Publication Date)
- Chapman and Hall/CRC(Publisher)
basic idea of feedback is simply to use the current state of a system to make decisions about the course of action for its future. Such a scheme is called “closed loop”, while a scheme where no information on the state of the system is used to influence its future operation is called “open loop”. An important form of feedback is Negative Feedback which we illus-trate through a common example: Heat Regulation. A simplified block diagram scheme of temperature regulation in a house is shown in Figure 28.4. In this scheme, it is desired to keep the temperature of a house (plant or process) at a certain reference temperature (set point). For this purpose, temperature is measured (sensor) and its deviation from the desired temperature is assessed (error signal). The error signal is then fed to the thermostat (controller) that devises that appropriate control action. The output of the controller is used to operate the heat fuel valve (actuator), therefore generating appropriate actuation signal (fuel to furnace). Errors or deviations from temperature setpoint are hence corrected through the action of this Negative Feedback. 28.6 Feedback Loops and Their Dynamic Role in Gene Reg-ulatory Networks Much like technological systems, gene regulatory networks need to operate robustly. Hence, it does not come much as a surprise that regulatory feedback loops are ubiquitously used in gene networks to tackle this robustness demand. In addition to robustness, feedback influences many other dynamical properties in these networks. We review some of these features in the following sections. 28.6.1 Feedback and Steady State Behavior Often times, the feedback structure in a system dictates its steady state behavior. Here, we focus on the role of feedback in creating monostability, multistability and periodic behavior.
eBook - PDFModels of Life
Dynamics and Regulation in Biological Systems
- Kim Sneppen(Author)
- 2014(Publication Date)
- Cambridge University Press(Publisher)
(B) If the Negative Feedback is delayed, the protein concentrations may oscillate in time. (C) Two types of indirect Negative Feedback, emphasizing, respectively, feedback through transcriptional repression, and the common feedback acting through protein–protein binding to a transcriptional activator. straightforward modification of Eq. (3.20) [389]: dR dt = leak + capacity 1 + (R/K) h − R τ (8.1) In a steady state, this results in an R that grows slower than linearly with increased capacity. Therefore the steady-state R is buffered against changes in cellular factors that affect capacity, a feature that makes a negative FL good for homeostasis. In addition, the 154 8 Feedback circuits Time R S S S E 0 1 E E R R R Figure 8.5 Negative Feedback in regulation of a metabolite “s” that is degraded/converted to another metabolite by an enzyme E [392]. The right-hand panel shows the response to a change in the source terms for s, from K s to 100 K s , at time > 0, where γ = 100 and R = 10. Time is counted in units of the exponential decay rate for the enzyme E, whereas the regulator is assumed to maintain constant total concentration throughout the simulation. The gray shaded area is “s” and the red curve shows 10 · E. The black line follows the concentration of free R. steady state is reached faster than in the absence of feedback [116, 390], as illustrated by Fig. 3.6 in Chapter 3. Negative Feedback systems are often seen between a metabolite and the regulatory system that controls its metabolism [392, 393, 394, 395, 396] (see Fig. 8.1A,B). The feedback is mediated by the binding of the small metabolite to a transcription regulator that subsequently changes properties, for example by making the regulator unable to bind to the operator. In that case, a Negative Feedback system involving regulator R, enzyme E and the metabolite s illustrated in Fig.
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