Body processes

Long Feedback Mechanism – Function, Task and Diseases

Long feedback mechanism

The long feedback mechanism is a principle of feedback that is relevant to hormone balance in the human body . One of the best-known long-feedback mechanisms is the control circuit between thyroid hormones and TSH ( thyrotropin ). Disorders within this control loop occur, among other things, in Graves’ disease .

What is the long feedback mechanism?

Feedback mechanisms in the sense of a self-regulating feedback play a role in the human body, especially for the hormone system. Hormones regulate their own release during self-adjustment. Different types of feedback exist. One of them is the long feedback mechanism, which corresponds to a physiological self-adaptation principle.

For example, long feedback plays a role in thyroid hormones and their effect on the release of thyrotropin-releasing hormone . In addition, the long feedback mechanism is a fundamental principle in the central control of the endocrine system. The hypothalamus is at the center of this control. The part of the brain belongs to the diencephalon and corresponds to the highest regulatory center of all vegetative and endocrine processes.

Essentially, two circuits play a role in the hormonal control processes through the hypothalamus. In addition to the short feedback mechanism , the hypothalamic adenopituitary loop or pituitary loop, this includes the adenopituitary or pituitary end organ loop, which corresponds to a long feedback mechanism.

function & task

In the human body there are different regulatory principles with feedback mechanisms, especially within the hormonal regulation. Different feedback levels are involved in this regulation. The hypothalamus is the supreme center of all hormonal feedback processes.

The brain area contains receptive areas that receive information from the environment, from the central nervous system and from the hormonal periphery of the body. The information from the body periphery usually corresponds to changes in hormone concentration. All of the above information is registered by the receptive fields of the hypothalamus.

The connection between the periphery and the hypothalamus represents a long-feedback mechanism. Ultimately, information from the hypothalamus reaches the pituitary gland . This can occur either neurogenic via the tuberohypophyseal tract or via the portal vascular system via hypophyseotropic hormones.

The latter is the case with the releasing hormones and inhibiting hormones of the hypothalamus. These hormones are control hormones that have a specific effect on the anterior pituitary gland. Examples of releasing hormones are the hormones GHRH, GnRH, CRH and THR. The hypothalamus does not receive feedback from the pituitary gland via a long, but rather a short feedback mechanism.

The long-feedback mechanism between the hypothalamus and the periphery also plays a role for the glandotropic hormones, which themselves represent an important regulatory principle within the endocrine feedback loop. Since the pituitary gland also receives feedback from the body’s periphery through a long-feedback mechanism, the gland can use this information to regulate the release of glandotropic hormones and thus influence the secretion of peripheral endocrine organs .

The hypothalamic-pituitary system is therefore subject to multiple feedback and determines the activity of all glands by using the regulatory principle of the glandotropic hormones. All regulatory levels of the system are controlled in terms of negative feedback. In short, the hormonal balance is organized in control circuits that continuously adapt to the body’s current hormone requirements. The hypothalamus-pituitary axis is the prime example of this principle.

The long feedback mechanism thus ultimately plays a role for all hormones and is ultimately also relevant for ovulation , for example. The long feedback effect of estrogens and progesterone is again in retroactive connection with the hypothalamus-pituitary system.

The female cycle thus has two important control components. In addition to the long-loop feedback of estrogens and progesterone to the system between the hypothalamus and pituitary gland, the pulsatile release of the hormones GnRH, LH and FSH plays a role in ovulation.

Diseases & Ailments

The disruption of a single hormone control circuit usually leads to disruption of the entire hormone balance and the associated bodily functions due to the close connections between individual control circuits. Hyperthyroidism or hypothyroidism ( hypero- and hypothyroidism) can result from a lack or excess of TSH, for example, and thus indicate a pituitary dysfunction .

The long-feedback mechanism between thyroid hormones and thyrotropin-releasing hormones establishes this connection. Likewise, TSH-producing tumors can cause an excess of TRH, which in turn disrupts the thyrotropic feedback loop.

Effects on the long-feedback mechanism between thyroid hormones and TRH are also shown by diseases such as Graves’ disease. The disease is associated with an overactive thyroid gland associated with autoimmune reactions. The patient’s immune system attacks the TSH receptors within the thyroid follicles . IgG-type antibodies bind to the receptors and permanently stimulate them, mimicking the action of TRH.

Due to the control circuits, this results in increased activity of the thyroid gland. There is an oversupply of thyroid hormones. In addition, the gland becomes larger and larger due to growth stimuli. Since the TSH present in the body is not effective due to its inability to bind to receptors, various bodily functions ultimately become unbalanced.

Due to the increased thyroid hormone concentration, the general TSH concentration decreases via the long feedback mechanism. At the same time, autoantibodies at the pituitary interfere with TSH secretion. Although the TSH concentration falls continuously, hyperthyroidism is present in the context of the disease.

Cushing ‘s syndrome also leads to disorders of the entire endocrine system. The disease is a disease of the hypothalamic-pituitary-adrenal axis. Tumors of the anterior pituitary often secrete ACTH, which stimulates high plasma levels of cortisol . Patients suffer from elevated blood sugar levels , which can be associated with type II diabetes mellitus .

Osteoporotic changes and muscle weakness can also occur. Trunk obesity with bull neck and full moon face are characteristic signs of Cushing’s syndrome.

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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.