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An effector is the target acted on, to bring about the change back to the normal state. At the cellular level, effectors include nuclear receptors that bring about changes in gene expression through up-regulation or down-regulation and act in negative feedback mechanisms. An example of this is in the control of bile acids in the liver. [4]
This is an example of a locally acting (negative feedback) mechanism. An example of upregulation is the response of liver cells exposed to such xenobiotic molecules as dioxin . In this situation, the cells increase their production of cytochrome P450 enzymes , which in turn increases degradation of these dioxin molecules.
Neuroendocrinology is the branch of biology (specifically of physiology) which studies the interaction between the nervous system and the endocrine system; i.e. how the brain regulates the hormonal activity in the body. [1]
It is therefore the plasma ionized calcium level which is tightly regulated to remain within very narrow limits by homeostatic negative feedback systems. Between 35 and 50% of the calcium in plasma is protein-bound, and 5–10% is in the form of complexes with organic acids and phosphates. The remainder (50–60%) is ionized.
The ECF composition is therefore crucial for their normal functions, and is maintained by a number of homeostatic mechanisms involving negative feedback. Homeostasis regulates, among others, the pH , sodium , potassium , and calcium concentrations in the ECF.
An example is a thermostat. In a living organism, reference values for controlled perceptual variables are endogenously maintained. Biological homeostasis and reflexes are simple, low-level examples. The discovery of mathematical principles of control introduced a way to model a negative feedback loop closed through the environment (circular ...
An implication of this is that transcription factors can regulate themselves. For example, in a negative feedback loop, the transcription factor acts as its own repressor: If the transcription factor protein binds the DNA of its own gene, it down-regulates the production of more of itself. This is one mechanism to maintain low levels of a ...
A simple negative feedback system is descriptive, for example, of some electronic amplifiers. The feedback is negative if the loop gain AB is negative.. Negative feedback (or balancing feedback) occurs when some function of the output of a system, process, or mechanism is fed back in a manner that tends to reduce the fluctuations in the output, whether caused by changes in the input or by ...