Negative feedback

Under the negative feedback a control loop is understood in which the output variable has an inhibiting effect on the input variable. In the human body, negative feedback is particularly important for the homeostasis of the hormonal balance. During the hormonal function test, the control loops are examined for errors.

What is the negative feedback?

The medical feedback is also called feedback and corresponds to a biological control loop. The output variable affects the input variable in these control loops. Feedback is predominantly negative in the human organism.

Negative feedback will be too Negative feedback called. In these control loops, the output variable has an inhibiting effect on the input variable. Because of this connection, the output variable of negative feedback loops is also referred to as a controller. The opposite of negative feedback is positive feedback, where the output amplifies the input.

The cybernetic system theory is used in medicine for the mathematical analysis of feedback loops.The negative feedback in the human organism is either subtractive inhibitions or divisive feedback with quotient inhibition. Both types of negative feedback, together with the positive feedback systems, take on regulatory tasks in the human body and thus control, for example, glandular secretion or the 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 & task

Negative feedback creates homeostasis. In this way you maintain the equilibrium in various systems within the permissible limits. The first step in negative feedback is always to measure a certain quantity. In the second step, the measurement results are used to reduce the respective values. Negative feedback is thus a regulator, as it plays a role, for example, in maintaining a constant body temperature in the organism of warm-blooded animals.

However, negative feedback is also crucial for processes of gene activity. The negative feedback control loops are just as important for the hormonal balance, the balance of which is crucial for many body functions. To keep the hormone secretion from the glands in balance, some hormones, for example, inhibit their own synthesis after they are released. 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 signal cascade inside.

The negative feedback mainly plays a role for the activity of the glandotropic cells within the adenohypophysis. Here, too, hormone synthesis is influenced by the current concentration of hormones in the blood. The synthesis of the blood hormones stimulates the control hormone of the adenohypophysis and thus throttles further hormone production either directly at the pituitary gland or via the hypothalamus.

The synthesis of the two hormones CRH and ACTH, for example, is more inhibited the higher the concentration of glucocorticoids in the blood. Similarly, the hormones TRH and TSH are synthesized less, the higher the thyroid hormone level in the blood.

The synthesis of FSH, GnRH and LH also has negative feedback. In men, a high blood level of FSH, LH and GnRH inhibits 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.

The central nervous system comes into action as a feedback control system and thus the top priority of all feedback, where the feedback systems are basically interconnected. In particular, the hormonal control circuits of the thyroid act directly on this control center and inhibit the release of hormone-stimulating substances in the hypothalamus.

Illnesses & ailments

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. During these inhibition and stimulation tests, the patient is injected with control hormones. If the administration of control hormones shows corresponding effects on the hormonal balance, then the control circuits and also the negative feedback in the organism are probably intact.

If hormonal feedback loops are not intact, then in the majority of cases there is a failure of the hormonal glands themselves. On the other hand, the higher-level control center can also be affected by functional losses and so, for example, no longer release organ-specific control hormones.

If negative feedback mechanisms in the hormonal system are not associated with organ diseases, but hormone production can no longer be regulated via the control loops, then degenerate 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, under certain circumstances, degenerate and thus disable the negative feedback control loops. However, this phenomenon is also very rare.

For disturbed control loops, a mutation of the control substances in negative feedback systems is theoretically possible. In the endocrine system, the mutation of leptin has recently been linked, for example, to obesity in young children.

Since biological control loops represent closely meshed networks, a feedback error in just one of the systems can also cause errors in the other systems. Hence, the symptoms of feedback error are extremely diverse. This is especially true for the hormonal system, since its control loops are in particularly close interaction. In addition to hormonal complaints, problems with the body's own thermoregulation can also be due to errors in the negative feedback.