Biological Sciences
Positive Feedback
Positive feedback is a process in which the output of a system amplifies the system's response, leading to an increase in the original stimulus. In biological systems, positive feedback loops are involved in processes such as blood clotting, childbirth, and the release of certain hormones. This amplifying effect can lead to rapid and sometimes dramatic changes within the system.
Written by Perlego with AI-assistance
Related key terms
1 of 5
4 Key excerpts on "Positive Feedback"
eBook - PDFFundamentals of Natural Computing
Basic Concepts, Algorithms, and Applications
- Leandro Nunes de Castro(Author)
- 2006(Publication Date)
- Chapman and Hall/CRC(Publisher)
Beneath all that apparent diversity, certain circuits repeat themselves over and over again. All these feedback and reverberating loops are believed to be neces-sary for learning, and are consequences of the high interconnectivity of the brain. Positive Feedback Positive Feedback is a sort of self-reinforcing (growth) process in which the more an event occurs, the more it tends to occur. Take the case of the immune system as an example. When a bacterium invades our organism, it starts repro-ducing and causing damage to our cells. One way the immune systems find to cope with these reproducing agents is by reproducing the immune cells capable of recognizing these agents. And the more cells are generated, the more cells can be generated. Furthermore, the immune cells and molecules release chemicals that stimulate other immune cells and molecules to fight against the disease-causing agent. Therefore, the response of some immune cells provides some sort of Positive Feedback to other immune cells reproduce and join the pool of cells involved in this immune response. The termite mound building behavior discussed previously is another example of a Positive Feedback mechanism. The more soil pellets are deposited in a given portion of the space, the more pellets tend to be deposited in that portion be-cause there is more pheromone attracting the termites (Figure 2.3). But these self-reinforcing (Positive Feedback) processes have to be regulated by negative feedback processes, otherwise the systems would go unstable or the resources would be depleted. Conceptualization 39 More termites More pheromone Figure 2.3: Example of Positive Feedback. There are several other examples of Positive Feedback in nature: • Human breeding : the more humans reproduce, the more humans exist to reproduce. • Feeding the baby : a baby begins to suckle her mother’s nipple and a few drops of milk are released, stimulating the production and release of more milk.
eBook - PDFFeedback Systems
An Introduction for Scientists and Engineers, Second Edition
- Karl Johan Åström, Richard Murray, Richard M. Murray(Authors)
- 2021(Publication Date)
- Princeton University Press(Publisher)
The examples given so far all deal with negative feedback , in which we attempt to react to disturbances in such a way that their effects decrease. Positive Feedback is the opposite, where the increase in some variable or signal leads to a situation in which that quantity is further increased through feedback. This has a destabilizing effect and is usually accompanied by a saturation that limits the growth of the quantity. Although often considered undesirable, this behavior is used in biological (and engineering) systems to obtain a very fast response to a condition or signal. Encouragement is a type of Positive Feedback that is very useful in both industry and academia. Another common use of Positive Feedback is in the design of systems with oscillatory dynamics. Feedback has many interesting properties that can be exploited in designing systems. As in the case of glucose regulation or the flyball governor, feedback can make a system resilient to external influences. It can also be used to create linear behavior out of nonlinear components, a common approach in electronics. More generally, feedback allows a system to be insensitive both to external disturbances and to variations in its individual elements. Feedback has potential disadvantages as well. It can create dynamic instabilities in a system, causing oscillations or even runaway behavior. Another drawback, especially in engineering systems, is that feedback can introduce unwanted sensor noise into the system, requiring careful filtering of signals. It is for these reasons that a substantial portion of the study of feedback systems is devoted to developing an understanding of dynamics and a mastery of techniques in dynamical systems. Feedback systems are ubiquitous in both natural and engineered systems.
eBook - PDF- Carlo Cosentino, Declan Bates(Authors)
- 2011(Publication Date)
- CRC Press(Publisher)
5 Positive Feedback systems 5.1 Introduction As seen in the previous chapter, negative feedback control loops play an im-portant role in enabling many different types of biological functionality, from homeostasis to chemotaxis. When evolutionary pressures cause negative feed-back to be supplemented with or replaced by Positive Feedback, other dynami-cal behaviours can be produced which have been used by biological systems for a variety of purposes, including the generation of hysteretic switches and oscil-lations, and the suppression of noise. Indeed, it has recently been argued that intracellular regulatory networks contain far more positive “sign-consistent” feedback and feed-forward loops than negative loops, due to the presence of hubs that are enriched with either negative or positive links, as well as to the non-uniform connectivity distribution of such networks, [1]. In the case studies at the end of this chapter we consider some of the types of biological functionality which may be achieved by Positive Feedback. First, however, we provide an introduction to some of the tools which are available to analyse these types of complex feedback control systems. 5.2 Bifurcations, bistability and limit cycles 5.2.1 Bifurcations and bistability In Chapter 3, we have seen that nonlinear systems can exhibit multiple equi-libria, each one being (either simply or asymptotically) stable or unstable. As can clearly be seen in Fig. 3.10, for example, the position of the equilibrium points, along with their stability properties and regions of attraction, deter-mine in large part the trajectories in the state-space, i.e. the behaviour of the system. On the other hand, nonlinearity also implies that the number and location of the equilibrium points, as well as their stability properties, vary with the parameter values. Therefore, it comes as no surprise that the behaviour of a 151
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.
Index pages curate the most relevant extracts from our library of academic textbooks. They’ve been created using an in-house natural language model (NLM), each adding context and meaning to key research topics.
