Feedback

In biology and medicine, feedback mechanisms are used to maintain various states of equilibrium within a system. This is also referred to as homeostasis. Such Feedback can be found in the body, for example, in maintaining body temperature and in the endocrine system. Feedback is also known as Feedback.

What is the feedback?

An example of positive feedback is milk production in women who have recently given birth. The suckling of the baby on the mother's breast stimulates the production of the hormone oxytocin.

When it comes to feedback, a distinction is made between negative and positive feedback processes. Negative feedback is mostly negative feedback. Here the output variable in the system has an inhibiting effect on the input variable. The positive feedback, on the other hand, belongs to the positive feedback processes.

The feedback mechanism is exactly the opposite of the negative feedback mechanism. The output variable here amplifies the input variable. An example of positive feedback is the so-called vicious circle.

Function & task

Feedback mechanisms are essential for maintaining balance within different body systems. Homeostasis (balance), on the other hand, is important so that all body processes can take place in a physiological way. For example, even small fluctuations in the blood pH value can have life-threatening consequences for the human body.

Negative feedback, a form of negative feedback, is an important element of the homeostatic control loop. The aim of negative feedback is to stabilize a certain variable within the control loop. A negative feedback always occurs when the end product in the control loop has an inhibitory, i.e. inhibiting, effect on the product which is at the beginning of the reaction chain.

So negative feedback is a self-reducing mechanism. This is one of the basic reactions in metabolic regulation and is therefore part of many processes in the body. An example of a negative feedback mechanism is the thyroid's hormonal control loop, also known as the thyroid control loop. The thyroid produces and stores the hormones triiodothyronine (T3) and tetraiodothyronine (T4). When and in what concentration the hormones are introduced into the blood is determined by the hormonal control circuit.

The hypothalamus and the pituitary gland play an important role in this control system. The pituitary gland measures the thyroid hormone level in the blood and releases the thyroid stimulating hormone (TSH) when there is a lack of T3 and T4. TSH, also known as thyrotropin, has a growth-stimulating effect on the thyroid gland and also stimulates the production of hormones. Conversely, too many thyroid hormones in the blood inhibit the release of TSH, so that the thyroid gland subsequently reduces its production of thyroid hormones.

In addition to this main control loop, there are other feedback loops in the thyroid control loop such as the Brokken-Wiersinga-Prummel control loop or regulation through feedback with the hypothalamus and the thyrotropin releasing hormone (TRH) produced there.

There is always positive feedback when the output variable has a reinforcing effect on itself in a system. It is part of the positive feedback. There are very few physiological positive feedback mechanisms in the body. An example of positive feedback is milk production in women who have recently given birth. The suckling of the baby on the mother's breast stimulates the production of the hormone oxytocin. This in turn stimulates the production of milk in the breast. As a result, the child drinks more, consequently more oxytocin is released and milk production increases again. If the child is no longer placed on the breast to drink, the oxytocin level drops and milk production decreases.

Pathological positive feedback processes in the form of a vicious circle are more common in the body.

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Illnesses & ailments

An example of a positive feedback mechanism in the course of a disease is heart failure. Heart failure is when the heart is no longer able to provide the blood volume required by the body. As a result, there is a reduced physical resilience. Common causes of heart failure are heart attacks, high blood pressure or atrial fibrillation. Heart valve defects can also result in heart failure.

The body tries to compensate for this heart failure by lowering the resistance of the blood vessels so that the heart has to exert less force when pumping. In addition, the heart's pumping capacity increases per minute, which means that the heart beats faster. However, due to the widening of the vessels, too little blood arrives in the peripheral blood vessels, for example in the kidney. In the kidney vessels, specialized cells register the blood pressure and, if the blood pressure is too low, use a hormonal control circuit, the renin-angiotensin-aldosterone system, to raise the blood pressure. To do this, more water is recovered from the urine, so that the blood volume and thus the pressure within the blood vessels increases. In order to pump the increased blood volume through the body, the damaged heart now has to exert even more force than before. The condition of the heart worsens, and heart failure increases.

However, illnesses in the body can also arise from disturbances in negative feedback loops. In the thyroid control loop, disturbances in the feedback lead to either an overactive thyroid or an underactive thyroid. With thyroid autonomy, the thyroid works completely independently of the control loop.

A disturbance in the control loop can also be triggered by an autoimmune disease. In Graves' disease, for example, the body produces so-called TSH receptor autoantibodies. These have the same effect on the thyroid gland as TSH in the pituitary gland, so that these TSH receptor autoantibodies lead to an increased production of thyroid hormones. The pituitary then no longer has any influence on the activities of the thyroid gland, the entire negative feedback mechanism remains completely ineffective. The result is hyperthyroidism with symptoms such as hair loss, diarrhea, heat intolerance, weight loss and osteoporosis.