In biology and medicine, feedback mechanisms serve to maintain various states of equilibrium within a system. This is also referred to as homeostasis. Such feedbacks are found in the body, for example, in the maintenance of body temperature and in the hormonal system. Feedback is also referred to as feedback.
What is feedback?
An example of positive feedback is milk production in women who have recently given birth. The infant’s sucking on the mother’s breast stimulates the production of the hormone oxytocin. In feedback, a distinction is made between counter- and co-feedback processes. In the case of negative feedback, this is usually negative feedback. Here, the output variable in the system has an inhibitory effect on the input variable. The positive feedbacks, on the other hand, belong to the positive feedback processes. The feedback mechanism is exactly opposite to the negative feedback mechanism. Here, the output variable amplifies the input variable. An example of a positive feedback is the so-called Circulus vitiosus.
Function and task
Feedback mechanisms are essential for maintaining equilibrium within various body systems. Homeostasis (balance), in turn, is important for all bodily processes to occur in a physiological manner. For example, even minor fluctuations in blood pH 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. Negative feedback always occurs when the end product in the control loop has an inhibitory effect on the product at the beginning of the reaction chain. Negative feedback is therefore a self-reducing mechanism. This belongs to the basic reactions in metabolic regulation and is thus part of many processes in the body. An example of a negative feedback mechanism is the hormonal control loop of the thyroid gland, also called the thyrotropic control loop. The thyroid gland produces and stores the hormones triiodothyronine (T3) and tetraiodothyronine (T4). When and in what concentration the hormones are released into the blood is determined by the hormonal control loop. The hypothalamus and the pituitary gland play an important role in this control loop. The pituitary gland measures thyroid hormone levels in the blood and releases Thyroid Stimulating Hormone (TSH) when T3 and T4 are deficient. TSH, also known as thyrotropin, has a growth-stimulating effect on the thyroid gland and also stimulates hormone production. Conversely, too many thyroid hormones in the blood inhibit the release of TSH, so that the thyroid gland consequently 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 with the thyrotropin releasing hormone (TRH) produced there. Positive feedback is always present when the output variable in a system has a reinforcing effect on itself. 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 in childbirth. The infant’s sucking on the mother’s breast stimulates the production of the hormone oxytocin. This in turn stimulates milk production in the breast. As a result, the baby drinks more, more oxytocin is consequently released and milk production increases again. If the child is no longer placed at 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.
Diseases and ailments
An example of a positive feedback mechanism in the course of a disease is heart failure. Heart failure is said to occur when the heart is no longer able to provide the volume of blood needed by the body. As a result, there is a reduced physical capacity. Common causes of heart failure are heart attack, high blood pressure or atrial fibrillation. Heart valve defects can also result in heart failure.The body now 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 per minute is increased, which means that the heart beats faster. However, as a result of the widening of the vessels, too little blood arrives in the peripheral blood vessels, for example in the kidneys. In the kidney vessels, specialized cells register the blood pressure and, if the blood pressure is too low, cause it to increase via a hormonal control circuit, the renin-angiotensin-aldosterone system. To achieve this, more water is recovered from the urine, so that the blood volume increases and with it the pressure within the blood vessels. To pump the increased blood volume through the body, the damaged heart must now exert even more force than before. The condition of the heart deteriorates and heart failure increases. However, diseases in the body can also result from disturbances in negative feedback loops. In the thyroid control circuit, disturbances in the feedback loop lead to either hyperthyroidism or hypothyroidism. In thyroid autonomy, the thyroid gland operates 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 the TSH of the pituitary gland, so that these TSH receptor autoantibodies lead to an increased production of thyroid hormones. The pituitary gland then no longer has any influence on the activities of the thyroid gland, and 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.