Endocrine secretion refers to the release of hormones or mediators (messengers) into the blood. The endocrine glands are responsible for secretion. The released agents are effective even at the lowest concentrations.
What is endocrine secretion?
Endocrine secretion refers to the release of hormones or mediators (messengers) into the blood. The endocrine glands, such as the adrenal glands, are responsible for secretion. Endocrine secretion represents the secretion of hormone-like agents or mediators by endocrine glands into the blood or lymph. Even very low concentrations of active substances exert major effects in the organism. The terms “endocrine gland” or “hormone gland” are used synonymously. Endocrine glands include specialized hormone glands, tissues with hormone-producing cells, specialized neurons and other organs involved in hormonal control function. Specialized endocrine glands secrete one or more hormones. In turn, there are hormones that act directly on the target organ or that control and regulate the formation of other hormones as part of a regulatory mechanism. In this way, regulatory circuits are formed in the organism that guarantee hormonal balance. Specialized hormone glands include the pituitary gland, the pineal gland, the thyroid gland, the parathyroid gland, the adrenal glands and the islet cells of the pancreas. Tissues with hormone-producing cells are found, for example, in the skin, heart, liver, gastrointestinal tract, and gonads (testes and ovaries). The hormones secreted by these tissues are tissue hormones that often act locally. The neurohormones secreted by the neurons are responsible for linking the nervous system to the endocrine system. The central neuroendocrine organ is the hypothalamus, which belongs to the brain and is the most important control center, controlling the autonomic nervous system while also regulating the endocrine system through important neurohormones.
Function and task
With the help of hormones and mediators, endocrine secretion controls all bodily processes in their entirety. It is subject to a regulatory circuit that ensures hormonal balance. Many hormones have their counterparts. For example, the hormone insulin lowers blood glucose levels. The counterpart is glycogen, which is also formed in the pancreas. Glucagon releases glucose under the breakdown of glucagon stored in the liver to keep blood glucose levels constant. The central endocrine organ is the pituitary gland. Several hormones with different functions are produced in the pituitary gland. The pituitary gland secretes hormones that act directly on organs, gonadotropic hormones, and non-gonadotropic hormones, among others. Direct-acting hormones secreted by the pituitary gland include growth hormone and prolactin. Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) function as gonadotropic hormones. Both hormones regulate ovulation in women and sperm maturation in men. Still other pituitary hormones stimulate the adrenal glands and thyroid to produce hormones. The glucocorticoid hormones cortisol, aldosterone, and small amounts of sex hormones are produced in the adrenal glands. While cortisol is responsible for catabolic metabolism, aldosterone regulates mineral balance. The thyroid gland in turn produces the thyroid hormones thyroxine and triiodothyronine. The hypothalamus functions as the central organ of the neuroendocrine regulatory mechanism. In addition to controlling the autonomic nervous system, the hypothalamus secretes various releasing and inhibiting hormones that regulate the formation of other hormones. In addition to the major hormonal regulatory circuits, there are other smaller regulatory circuits through which the formation and inhibition of tissue hormones are regulated. At the same time, however, all regulatory circuits are interconnected. Overall, hormonal processes are subject to very complicated regulatory mechanisms, the details of which are not yet known. New hormones are still being discovered on a regular basis. Also, more and more organs have to be counted at least partially among the endocrine organs. According to recent findings, adipose tissue, for example, represents the largest endocrine organ. For example, changes in the volume of fat cells due to fat intake or fat breakdown have a major impact on the effectiveness of insulin.
Diseases and ailments
In connection with endocrine secretion, there are various clinical pictures that are often not recognized as hormonal disorders. Already insulin resistance can also be explained by hormonal processes according to recent findings. For example, if existing fat cells become larger and larger due to fat intake, the concentration of the peptide hormone adiponectin decreases more and more. The exact mode of action of this hormone is not yet known. However, it has been established that adiponectin reduces insulin resistance. Since more adiponectin is produced as the cell volume of the fat cells decreases, this also increases the effectiveness of insulin again. Classic examples of hormone disorders are Cushing’s syndrome or adrenocortical insufficiency (Addison’s disease). In Cushing’s syndrome, too much cortisol is produced. Cortisol is a stress hormone secreted in the adrenal cortex. Overproduction can be caused primarily by a tumor of the adrenal cortex or secondarily by hormonal dysregulation. Symptoms of Cushing’s syndrome include weakening of the immune system, susceptibility to infections, increase in blood glucose levels, and development of truncal obesity with a full moon face. Addison’s disease is characterized by an underactivity of the adrenal cortex. The hormones of the adrenal cortex (cortisol, aldosterone) and the sex hormones are no longer produced in sufficient quantities. As a result, there is a lack of strength, weakness and hyperpigmentation of the skin. The skin becomes bronze colored. The missing hormones must be substituted for life. Addison’s disease can also be caused by primary or secondary adrenal insufficiency. The secondary form of the disease is caused by an insufficiency of the pituitary gland, when the hormone ACTH, which stimulates the adrenal cortex, is no longer sufficiently produced. Furthermore, many forms of hyperthyroidism or hypothyroidism occur. Here, too, there may be primary and secondary causes for the respective disorder.
