Human endocrine system: anatomical and physiological reference

Humanism is a complex self-regulating system, each function in which only at first glance may seem autonomous. In fact, any process that occurs at the cellular level is well regulated, ensuring the maintenance of internal homeostasis and optimal balance. One of these regulatory mechanisms is hormonal status, which is provided by the endocrine system – a complex of cells, tissues and organs responsible for the transmission of “information” by changing the level of hormones. How does this system work? How does it fulfill the functions assigned to it? And how is endocrine activity regulated? Let’s try to figure it out!

The human endocrine system: briefly about the main

The endocrine system is a complex multicomponent structure that includes individual organs, as well as cells and groups of cells that are able to synthesize hormones, thereby regulating the activity of other internal organs. The endocrine glands do not have excretory ducts. They are surrounded by numerous nerve fibers and blood capillaries, thanks to which the transfer of synthesized hormones is carried out. Released, these substances penetrate into the blood, intercellular space and adjacent tissues, affecting the functionality of the body.

This feature is key in the classification of glands. The organs that carry out external secretion have excretory ducts on the surface and inside the body, and mixed secretion implies the spread of hormones in both ways. Thus, adaptation to constantly changing external conditions and maintenance of the relative constancy of the internal environment of the human body is carried out.

Endocrine system: structure and function

The functionality of the endocrine system is clearly divided between organs that are not interchangeable. Each of them synthesizes its own hormone or several, performing strictly defined actions. Based on this, the entire endocrine system is easier to consider, classifying into groups:

  • Glandular – the group is represented by formed glands that produce steroid, thyroid and some peptide hormones.
  • Diffuse – a feature of this group is the spread of individual endocrine cells throughout the body. They synthesize aglandular hormones (peptides).

If the glandular organs have a clear localization and structure, then diffuse cells are scattered in almost all tissues and organs. This means that the endocrine system covers the entire body as a whole, precisely and thoroughly regulating its functions by changing the level of hormones.

endocrine system anatomy

Functions of the human endocrine system

The functionality of the endocrine system is largely determined by the properties of the hormones that it produces. So, the following directly depends on the normal activity of the glands:

  • adaptation of organs and systems to constantly changing environmental conditions;
  • chemical regulation of the functions of organs through the coordination of their activity;
  • preservation of homeostasis;
  • interaction with the nervous and immune systems in matters related to the growth and development of a person, his gender differentiation and the ability to reproduce;
  • regulation of energy exchange, starting with the formation of energy resources from the available kilocalories and ending with the formation of the body’s energy reserves;
  • correction of the emotional and mental sphere (together with the nervous system).

Organs of the human endocrine system

As mentioned above, the human endocrine system is represented by both individual organs and cells and groups of cells localized throughout the body. Full-fledged isolated glands include:

  • hypothalamic-pituitary complex,
  • thyroid and parathyroid glands,
  • adrenal glands,
  • pineal gland,
  • pancreas,
  • genital gonads (ovaries and testes),
  • thymus.

In addition, endocrine cells can be found in the central nervous system, heart, kidneys, lungs, prostate and dozens of other organs, which together form a diffuse compartment.

endocrine system

Glandular endocrine system

The endocrine glandular glands are formed by a complex of endocrine cells capable of producing hormones, thereby regulating the activity of the human body. Each of them synthesizes its own hormones or a group of hormones, the composition of which determines the function performed. Let’s consider in more detail each of their endocrine glands.

Hypothalamic-pituitary system


The hypothalamus and pituitary gland in anatomy are usually considered together, since both of these glands perform joint activities, regulating vital processes. Despite the extremely small size of the pituitary gland, which usually weighs no more than 1 gram, it is the most important coordinating center for the entire human body. It is here that hormones are produced, on the concentration of which the activity of almost all other glands depends.

Anatomically, the pituitary gland consists of three microscopic lobes: the adenohypophysis located in front, the neurohypophysis located in the back, and the median lobe, which, unlike the other two, is practically undeveloped. The most significant role is played by the adenohypophysis, synthesizing 6 key dominant hormones:

  • thyrotropin – affects the activity of the thyroid gland,
  • adrenocorticotropic hormone – responsible for the functionality of the adrenal glands,
  • 4 gonadotropic hormones – regulate fertility and sexual function.

In addition, the anterior lobe of the pituitary gland produces somatotropin, a growth hormone, the concentration of which directly affects the harmonious development of the skeletal system, cartilage and muscle tissue, and hence the proportionality of the body. An excess of somatotropin caused by excessive activity of the pituitary gland can lead to acromegaly – abnormal growth of limbs and facial structures.

The posterior lobe of the pituitary gland does not produce hormones on its own. Its function is to influence the pineal gland and its hormonal activity. The hydrobalance in the cells and the contractile ability of smooth muscle tissues directly depend on how developed the posterior lobe is.

In turn, the pituitary gland is an irreplaceable ally of the hypothalamus, providing communication between the brain, nervous system and blood vessels. This functionality is due to the activity of neurosecretory cells that synthesize special chemicals.



The thyroid gland, or thyroid gland, is located in front of the trachea (right and left) and is represented by two lobes and a small isthmus at the level of the 2nd to 4th cartilaginous ring of the windpipe. Normally, iron is very small in size and weighs no more than 20-30 grams, however, in the presence of endocrine diseases, it can increase 2 or more times – it all depends on the degree and characteristics of the pathology.

The thyroid gland is quite sensitive to mechanical stress, therefore it needs additional protection. In front, it is surrounded by strong muscle fibers, in the back – the trachea and larynx, to which it is attached by a fascial bursa. The body of the gland consists of connective tissue and numerous rounded vesicles filled with a colloidal substance rich in protein and iodine compounds. This substance also includes the most important thyroid hormones – triiodothyronine and thyroxine. The intensity and rate of metabolism, susceptibility to sugars and glucose, the degree of lipid breakdown and, as a result, the presence of fat deposits and excess body weight directly depend on their concentration.

Another thyroid hormone is calcitonin, which normalizes calcium and phosphate levels in cells. The action of this substance is antagonistic to the parathyroid hormone – parathyroidin, which, in turn, increases the flow of calcium from the skeletal system into the blood.

Parathyroid gland

A complex of 4 small glands located behind the thyroid gland forms the parathyroid gland. This endocrine organ is responsible for the calcium status of the body, which is necessary for the full development of the body, the functioning of the motor and nervous systems. Regulation of the level of calcium in the blood is achieved by hypersensitive cells of the parathyroid gland. As soon as the calcium status decreases, beyond the permissible level, the iron begins to produce parathyroid hormone, which triggers the release of mineral molecules from bone cells, replenishing the deficiency.

Adrenal glands

Each of the kidneys has a peculiar “cap” of a triangular shape – the adrenal gland, consisting of a cortical layer and a small amount (about 10% of the total mass) of the medulla. The cortex of each adrenal gland produces the following steroid substances:

  • mineralocorticoids (aldosterone, etc.), which regulate cellular ion exchange to ensure electrolyte balance;
  • glycocorticoids (cortisol, etc.), which are responsible for the formation of carbohydrates and the breakdown of proteins.

In addition, the cortical substance partially synthesizes androgens – male sex hormones, which are present in different concentrations in the organisms of both sexes. However, this function of the adrenal glands is rather secondary and does not play a key role, since the main part of sex hormones is produced by other glands.

kidneys and adrenal glands

The adrenal medulla has a completely different function. It optimizes the sympathetic nervous system by producing a certain level of adrenaline in response to external and internal stimuli. This substance is often referred to as the stress hormone. Under its influence, a person’s pulse quickens, blood vessels narrow, pupils dilate and muscles contract. Unlike the cortex, the activity of which is regulated by the central nervous system, the adrenal medulla is activated under the influence of peripheral nerve nodes.


The study of the epiphyseal region of the endocrine system is carried out by anatomical scientists to this day, since the full range of functions that this gland can perform has not yet been determined. It is only known that melatonin and norepinephrine are synthesized in the pineal gland. The first regulates the sequence of sleep phases, indirectly influencing the wakefulness and rest of the body, physiological resources and the possibility of restoring energy reserves. And the second affects the activity of the nervous and circulatory systems.

pineal gland


In the upper part of the abdominal cavity, there is another endocrine gland – the pancreas. This gland is an oblong organ located between the spleen and the duodenal part of the intestine, an average length of 12 to 30 centimeters, depending on the age and individual characteristics of the person. Unlike most endocrine organs, the pancreas produces more than just hormones. It also synthesizes pancreatic juice, which is necessary for the breakdown of food and normal metabolism. Thanks to this, the pancreas belongs to a mixed group that secretes synthesized substances into the blood and into the digestive tract.

Round epithelial cells (islets of Langengars), localized in the pancreas, provide the body with two peptide hormones – glucagon and insulin. These substances perform antagonistic functions: getting into the blood, insulin reduces the level of glucose contained in it, and glucagon, on the contrary, increases it.


Sex glands

The gonads, or sex endocrine glands, in women are represented by the ovaries, and in men, respectively, by the testes, which produce most of the sex hormones. In childhood, the function of the gonads is insignificant, since the levels of sex hormones in the organisms of babies are not so high. However, already by adolescence, the picture changes dramatically: the level of androgens and estrogens increases several times, due to which secondary sexual characteristics are formed. As we grow older, the hormonal status gradually levels out, determining the reproductive functions of a person.

sex glands


This endocrine gland plays a certain role only until the moment of puberty of the child, after which it gradually decreases the level of functionality, giving way to more developed and differentiated organs. The function of the thymus is the synthesis of thymopoietins – soluble hormones, on which the quality and activity of immune cells, their growth and an adequate response to pathogenic processes depend. However, with age, the tissues of the thymus are replaced by connective fibers, and the gland itself is gradually reduced.

Thymus, thymus gland

Diffuse endocrine system

The diffuse part of the human endocrine system is unevenly dispersed throughout the body. Revealed a huge amount of hormones produced by the glandular cells of the organs. However, the most important in physiology are the following:

  • liver endocrine cells, which produce insulin-like growth factor and somatomedin, which accelerates protein synthesis and promotes muscle gain;
  • the renal region, which produces erythropoietin for normal production of red blood cells;
  • gastric cells – gastrin is produced here, which is necessary for normal digestion;
  • intestinal glands, where vasoactive interstinal peptide is formed;
  • endocrine cells of the spleen, which are responsible for the production of splenins – hormones necessary for the regulation of the immune response.

This list can be continued for a very long time. Only in the gastrointestinal tract, thanks to endocrine cells, more than three dozen different hormones are produced. Therefore, despite the lack of clear localization, the role of the diffuse system in the body is extremely important. It depends on it how high-quality and stable the body’s homeostasis will be in response to stimuli.

How the human endocrine system works

Hormonal balance is the basis for the constancy of the internal environment of the human body, its normal functionality and life, and the work of the endocrine system plays a key role in this. Such self-regulation can be viewed as a chain of interrelated mechanisms, in which the level of one substance causes changes in the concentration of another and vice versa. For example, an increased level of glucose in the blood provokes the activation of the pancreas, which in response produces more insulin, leveling the existing surplus.

Nervous regulation of the endocrine glands is also carried out due to the activity of the hypothalamus. Firstly, this organ synthesizes hormones that can have a direct effect on other endocrine glands – the thyroid gland, adrenal glands, sex glands, etc. And secondly, the nerve fibers surrounding the gland react violently to changes in the tone of the adjacent blood vessels, due to what endocrine activity can increase or decrease.

Modern pharmacology has learned to synthesize dozens of hormone-like substances that can compensate for the lack of a particular hormone in the body by adjusting certain functions. And yet, despite the high effectiveness of hormone therapy, it is not devoid of a high risk of side effects, addiction and other unpleasant symptoms. Therefore, the main task of endocrinology is not to select the optimal medication, but to maintain the health and normal functionality of the glands themselves, because not a single synthetic substance is able to 100% recreate the natural process of hormonal regulation of the human body.