As a complex system, the hormone system controls the coordination of the functions of all organs of the organism. In humans, over thirty different hormones (messenger substances) are responsible for this. The medical specialty of endocrinology deals with the disorders within the endocrine system.
What is the endocrine system?
The endocrine system includes both endocrine glands and isolated groups of cells in other organs that produce what are called hormones (messenger substances). These hormones are either delivered endocrine via the bloodstream to the target organs or already have a paracrine effect on neighboring cells. Within the endocrine system, the production of the individual hormones is well coordinated. Thus, there are messenger substances that act directly on the target organs. Other hormones have regulatory functions. They control the production of other hormones. The hormone system is linked to the central nervous system via the hypothalamus. The hypothalamus is considered the superior control organ of all endocrine glands and produces releasing and inhibiting factors (hormones that promote or inhibit downstream hormone production). The basis of its function is the conversion of processed sensory impressions into physical reactions via the endocrine system. The close coupling of the nervous system with the endocrine system is summarized under the term neuroendocrine system.
Anatomy and structure
The endocrine system consists of various endocrine glands distributed throughout the body and isolated hormone-producing cell groups from other organs. Endocrine glands include the pituitary gland, thyroid gland, parathyroid gland, pineal gland, adrenal gland, or islets of Langerhans from the pancreas. Corpus luteum, ovarian follicles in the ovary and Leydig’s intermediate cells in the testis are also part of the endocrine system, as are the paraganglia, which, as a collection of nerve cell bodies, link the endocrine system and the nervous system together to form the neuroendocrine system as a result of their partial endocrine function. Furthermore, all epithelia contain endocrine cells, but their hormones mostly act paracrine (on the neighboring tissue). The pituitary gland (hypophysis) represents the link between the hypothalamus and the subordinate endocrine glands. While the hypothalamus, as part of the cerebellum, still belongs to the central nervous system, the pituitary gland is already an endocrine gland. It can thus be considered a link between the nervous system and the endocrine system. The pituitary gland produces a number of hormones that control or act directly on the target organ. As a central endocrine organ, it controls the functions of the other endocrine glands. The production of the individual hormones is controlled via a regulatory circuit. For example, if there are too few thyroid hormones, the pituitary gland is stimulated to produce the thyroid-stimulating hormone TSH. The same is true in reverse. For example, in addition to the thyroid gland, the adrenal glands or gonads are also subject to this regulatory mechanism within the hormonal system.
Function and tasks
The messenger substances produced within the endocrine system each exert individual functions on the target organs. For example, the pancreatic islets of Langerhans are responsible for the production of insulin. Insulin regulates blood glucose levels. A deficiency of insulin results in diabetes. The thyroid gland, in turn, produces thyroid hormones that stimulate metabolism. Thus, metabolism slows down when there is a thyroid hormone deficiency. Conversely, when there is an excess of thyroid hormones, metabolism speeds up. The sex hormones in turn regulate the primary and secondary formation of sexual characteristics and significantly influence sexual behavior. Various glucocorticoids are produced in the adrenal glands. These are steroid hormones whose basic building block is cholesterol. Glucocorticoids fulfill different tasks. They affect the metabolism, are responsible for mineral balance, influence the cardiovascular system and have an anti-inflammatory and immunosuppressive effect. Cortisol as a representative of the glucocorticoids controls, for example, gluconeogenesis (conversion of proteins into carbohydrates). The hormones produced (anterior pituitary) or stored (posterior pituitary) in the pituitary gland have different functions. For example, STH (somatotropin, growth hormone), prolactin or melanotropin act directly on the organs of success. Somatropin regulates growth.Prolactin is responsible for milk production during lactation and melanotropin stimulates the growth of melanocytes. The hormones TSH, ACTH, FSH and LH stimulate the thyroid gland, the adrenal cortex or the gonads, in that order. In the neurohypophysis (posterior lobe of the pituitary gland), the hormones vasopressin and oxytocin, which originate from the hypothalamus, are stored and released when needed. While vasopressin (antidiuretic hormone) regulates water reabsorption in the kidneys, oxytocin is responsible for the contraction of uterine smooth muscle during labor. Various scattered endocrine cells of the endocrine system in the heart, kidneys, liver, gastrointestinal tract, thymus, central nervous system, and other organs each exert specific functions.
Diseases
Diseases within the endocrine system manifest in different ways. If specific organs are affected, there may be deficiency, failure, or excess of individual hormones with the corresponding health disorders. An insulin deficiency, for example, causes diabetes. In the case of hypothyroidism, metabolism slows down and with it all bodily functions. Hypothyroidism is manifested by severe weight loss, nervousness, higher heart rate and diarrhea. An overproduction of cortisol causes the so-called Cushing’s syndrome with truncal obesity and increased susceptibility to infections. Loss of adrenal function results in potentially life-threatening Addison’s disease due to cortisol deficiency as well as mineral corticoid deficiency. If the anterior pituitary gland fails, a whole series of hormones are affected at once. The functional failure of the adenohypophysis, known as Sheehan’s syndrome, manifests itself as a combination of symptoms of various hormone deficiencies. Often, lifelong hormone replacement is required. If the sex hormones are affected by hormone imbalances, hypogonadism, sexual dysfunction, or infertility often result. Because the endocrine system and nervous system are closely linked, psychological disorders can also affect the endocrine system.
