Negative feedback refers to a control loop in which the output variable has an inhibitory effect on the input variable. In the human body, negative feedback is particularly crucial for hormonal homeostasis. In hormonal function testing, the control loops are examined for errors.
What is negative feedback?
In the human body, negative feedback is especially crucial for hormone homeostasis. Medical feedback is also called feedback and corresponds to a biological control loop. In these control loops, the output variable acts back on the input variable. Feedbacks are predominantly negative in human organisms. Negative feedbacks are also called negative feedbacks. In these control loops, the output variable has an inhibiting effect on the input variable. Because of this, the output variable of negative feedback loops is also called a regulator. The opposite of negative feedback is positive feedback, where the output variable amplifies the input variable. In medicine, cybernetic systems theory is used for the mathematical analysis of feedback loops. The negative feedbacks in the human organism are either subtractive inhibition or divisive feedback with quotient inhibition. Both types of negative feedback, together with the positive feedback systems, perform regulatory tasks in the human body, controlling, for example, glandular secretion or hormone balance. In the field of technology, negative feedback is used in the sense of a control loop, for example, for temperature regulation by a thermostat.
Function and task
Negative feedbacks establish homeostasis. They thus maintain equilibrium in various systems within permissible limits. The first step of a negative feedback is always the measurement of a certain quantity. In the second step, the results of the measurement are each used to lower the respective quantities. Negative feedbacks are thus regulators, such as those that play a role in maintaining a constant body temperature in the organism of warm-blooded animals. However, negative feedbacks are also crucial for processes of gene activity. Equally important are the negative feedback control circuits for hormone balance, the equilibrium of which is crucial for many bodily functions. For example, to keep hormone secretion from glands in balance, some hormones inhibit their own synthesis after release. These hormones are also known as autocrine. The secreting cells of autocrine hormones are themselves equipped with receptors to which the respective hormone can bind and trigger a signaling cascade inside. Countercoupling plays a role primarily in the activity of glandotropic cells within the adenohypophysis. Hormone synthesis is also influenced here by the current concentration of hormones in the blood. Synthesis of the blood hormones stimulates the control hormone of the adenohypophysis and thus throttles further hormone production either directly at the pituitary or via the hypothalamus. For example, the synthesis of the two hormones CRH and ACTH experiences a stronger inhibition the higher the concentration of glucocorticoids in the blood. Similarly, the higher the level of thyroid hormones in the blood, the less the hormones TRH and TSH are synthesized. The synthesis of FSH, GnRH and LH is also negatively feedback regulated. In males, high blood levels of FSH, LH and GnRH inhibit synthesis. In women, on the other hand, a high concentration of estrogens, FSH and LH has an inhibitory effect on the synthesis of these hormones. As a feedback control system and thus the highest point of all feedbacks, the central nervous system comes into action, where the feedback systems are connected in a basic way. Specifically, the hormonal control circuits of the thyroid gland act directly on this control center and inhibit the release of hormone-stimulating substances in the hypothalamus.
Diseases and disorders
Various events and diseases damage the hormonal control circuits and thus many negative feedback mechanisms in the human body. The hormonal function test checks whether the hormonal control circuits are intact. The patient is injected with control hormones during these inhibition and stimulation tests. If the administration of control hormones shows corresponding effects on the hormonal balance, then the control circuits and also the negative feedback mechanisms in the organism are probably intact.If hormonal feedback circuits are not intact, in a majority of cases there is a failure of the endocrine glands themselves. On the other hand, the higher-level control center may also be affected by loss of function and thus, for example, no longer secrete organ-specific control hormones. If negative feedback mechanisms in the hormone system are not associated with organ diseases, but hormone production can nevertheless no longer be regulated via the control circuits, degenerated hormone cells may be the cause of the regulatory problems. However, the degeneration of hormone cells, such as those in the thyroid gland, is rather rare. The hormones themselves can also degenerate under certain circumstances and thus disable the negative feedback control circuits. However, this phenomenon is also very rare. Theoretically, a mutation of the regulatory substances in negative feedback systems is also a possibility for disturbed regulatory circuits. In the endocrine system, the mutation of leptin has recently been associated with obesity in young children, for example. Because biological control circuits are tightly meshed networks, a feedback error in just one of the systems can also cause errors in the other systems. Therefore, the symptoms of feedback errors are extremely broad. This is especially true for the endocrine system, since its regulatory circuits are in particularly close interaction. In addition to hormonal complaints, problems with the body’s thermoregulation can also result from errors in negative feedback.
