Through the secretion of hormones, the endocrine system comprehensively regulates the functional activities closely related to the basis of individual survival, such as maintaining the metabolism of tissue cells, regulating the growth, development, reproduction and aging process of the body, etc. Therefore, it is the body's regulatory system, interacting with the regulatory functions of the nervous system and the immune system to regulate and maintain the balance of the body from different aspects.


Endocrine and Endocrine System


Endocrine refers to a form of secretion in which gland cells secrete substances directly into body fluids such as blood or extracellular fluid, and regulate target cells with them as the medium. Cells with this function are called endocrine cells. Typical endocrine cells are concentrated in the pituitary gland, thyroid gland, parathyroid gland, adrenal gland and pancreatic islets, forming the endocrine glands. Studies have shown that atypical endocrine cells, such as neurons, heart muscle, vascular endothelium, liver, kidney, fat, and immune cells also produce hormones. Endocrine is not only a form of secretory expression, but an integrated functional activity of the body to release regulatory information by secreting hormones. 


 Endocrine system


The endocrine system consists of the classical endocrine glands and the organs and tissues that produce hormone. It is a regulatory system that releases information and integrates the function of the body. The endocrine system can feel the stimulation of internal and external environment, and finally produce regulatory effects through hormones as chemical messengers.


The endocrine system not only performs its functions independently, but also interacts with the nervous and immune systems to form a complex neuro-endocrino-immune regulatory network, which jointly plays a holistic regulatory function to maintain the stability of the body's internal environment. These three systems perform their functions, regulate each other and complement each other. By sensing various changes in the internal and external environment, they comprehensively process and store information, to integrate the functions of the body and ensure the operation of life activities of the body.




Hormones are highly potent bioactive substances synthesized and secreted by endocrine cells in endocrine glands or organs. They transmit regulatory information between cells through body fluids. According to the classical concept, hormones transmit their regulatory information to distant target cells through blood flow to achieve long-distance communication. Therefore, endocrine is also called telecrine or hemocrine. Modern research has shown that hormones can also be released into the body cavity and nearby cells through paracrine, neuroendocrine and autocrine and be used to transmit information.



Epinephrine -- one of the catecholamine hormones


Sources of Hormones


Hormones mainly come from the following aspects: classical endocrine glands, such as pituitary, thyroid, parathyroid, islet, adrenal gland, gonad, etc.; secretion of non-endocrine gland organs, including brain, heart, liver, kidney, gastrointestinal tract and other organs, some cells have endocrine functions in addition to their specific functions. For example, cardiac cells can generate natriuretics in some tissues and organs, angiotensin II and 1, 25-dihydroxyvitamin D3 are converted into bioactive hormones in lung and kidney tissues, respectively.


Regulating the Effect of Hormones on the Overall Function of the Body


1. Maintain body homeostasis. Hormones participate in the regulation of water, electrolytes and acid-base balance and maintain the relative stability of body temperature, blood pressure and other processes, and directly participate in stress, coordinate and complement the nervous system and immune system, comprehensively regulate body functions, and adapt to environmental changes.

2. Regulate metabolism. Most hormones regulate the intermediate metabolism and energy metabolism of tissue cells, maintain the balance of nutrition and energy, and lay the foundation for various life activities of the body.

3. Promote growth and development. It can promote the growth, proliferation and differentiation of tissues and cells in the whole body, participate in the process of cell apoptosis, and regulate the normal growth, development and functional activities of various systems and organs.

4. Regulate the reproductive process. Promote the normal development and maturation of reproductive organs and the whole process of reproduction, maintain the generation of germ cells until the process of pregnancy and lactation, to ensure the continuity of individual life and germline reproduction.


Chemical Nature of Hormones


Hormone molecules are diverse and complex. The chemistry of a hormone determines its mode of action on target cells. According to the chemical structure of hormones, they can be divided into three categories: amines, peptides or proteins, and lipid hormones. Peptide or protein hormones and most amine hormones belong to nitrogenous hydrophilic hormones. They bind to target cell membrane receptors and have regulatory effects on target cells. Lipophilic hormones such as steroid hormones and thyroid hormones can directly enter the target cells to their roles.


Mechanism of Action of Hormones


The regulatory effect of hormones on target cells mainly goes through the following steps:

1. Receptor recognition. Target-cell receptors recognize hormones that bind to them from a wide range of chemicals in body fluids.

2. Signal transduction. The hormone binds to specific receptors in target cells and initiates intracellular signal transduction systems.

3. Cell response. Hormone-induced terminal signals change the intrinsic function of cells, that is, produce regulatory effects.

4. Effect terminates. The cellular biological responses induced by hormones are terminated by a variety of mechanisms.

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