Endocrine System

Do you know what the word “organ” means in the biological sense and what the “organ system”is?

I suspect that almost all readers will answer this question in the affirmative.

Then here’s another question – the head, hand and heart are the organs?

The correct answer would be: of all the above, only the heart is the organ. Arms and legs belong to the limbs, separated from the body paired appendages of the body. And the head is a part of the body in which there are several organs – the brain, eyes, tongue and so on.

There is a tricky question that anatomy teachers like to ask freshmen: “is the Ear a part of the body or a limb?”.

At first glance, the ear – like extremity, because it is separate from the body of paired appendage. Funny? But it’s logical, isn’t it?

On second glance, the ear – like part of the body, since it performs two functions: perceive sound vibrations and provides the ability to keep balance (in my ear, if someone does not know, is the vestibular apparatus, the organ perceiving changes in head position and body in space and the direction of movement of the body).

But it would be right to call the ear an organ. A complex body with several functions. And what we call the “ear” in everyday life, that is – the ear, in the anatomical sense is the outer part of the body called “ear”.

Now, let’s be clear. An organ in biology and medicine is a part of the body that performs certain functions, one or more. The heart, for example, a function of just one (if not to delve deeply into the scientific jungle) – through the cuts to ensure the flow of blood through the blood vessels. And the lungs have several functions. In addition to its main function – gas exchange between atmospheric air and blood, the lungs provide air flow to create voice sounds, serve as a protective barrier that prevents the penetration of pathogens of a number of infections into the body, and also serve as a reservoir for the accumulation of blood, one of the so-called “blood depots” or “blood depots”. The vessels of the lungs are easily extensible and contain a fairly large amount of blood.

The set of organs involved in one common function is called the organ system. Key words: “one common function”. The heart and lungs can not belong to one system, because one organ pumps blood, and the other carries out gas exchange. But the lungs and trachea belong to the same system certainly, because they perform a common function.

In the human body, the following organ systems are distinguished:

• nervous;

• endocrine;

• digestive;

• respiratory;

• urinary;

• musculoskeletal;

• integumentary;

• circulatory;

• lymphatic;

• immune, which includes in addition to the immune system hematopoietic organs;

• sexual;

• sensory (sense organs).

All systems are important, all systems are necessary, but there are two systems that can be called the most important – it is the nervous and endocrine systems. “The most important” they are considered because they regulate and coordinate the work of other systems. We can say that the nervous and endocrine systems are systems-leaders, and the rest of the system – performers.

What do you think – can the same body relate to different systems?

Can, of course, can, if it has the appropriate functions. For example, the urethra (Yes, if someone does not know, it is – a separate body) in men refers to both the urinary and sexual systems.

The General review of organ systems ends here.

We will now take a closer look at the endocrine system. Without this acquaintance, we have no talk about hormones will not work, and will only empty meaningless and pointless chatter. But we need something substantive and meaningful, right?

The endocrine system consists of endocrine glands…

Stop! Several questions arise at once.

What is endocrine gland?

Are there glands of external secretion?

If there are, then how are the glands of external and internal secretion different from each other?

It’s simple.

All three questions can be answered in one sentence. If the gland has excretory ducts through which its secret is released outwards or into some cavity of the body, it refers to the glands of external secretion, if not, it refers to the glands of internal secretion.

There is a fourth question: “How, that is – where, secrete their secret endocrine glands, if they have no ducts?»

Directly in washing their blood secrete. The cell secretes the produced secret into the intercellular space, from where it is absorbed into the blood.

The relationship between the cells of the endocrine glands and blood can be compared with the relationship of the employee and the employer. The employer-blood provides cells with food, delivering them oxygen, glucose and other necessary substances for life, and the cells produce hormones that the blood takes away from them. Such here is is is obtained mutually beneficial cooperation.

The mammary or salivary glands are the glands of external secretion, because they have ducts. The thyroid gland does not have ducts and is therefore considered an internal secretion gland.

Glands of external secretion called exocrine. This name is formed from the Greek words “Exo” – out and “crino” – I allocate. Endocrine glands are called endocrine glands, as “endo” means inside. Hence, “endocrinology” is the study of glands of internal secretion.

The endocrine system consists of the following endocrine glands:

• thyroid;

• parathyroid;

• thymus (thymus));

• pituitary;

• hypothalamus;

• epiphysis;

• pancreas;

• adrenals;

• paraganglia;

• sex glands – testicles (testes) in men and ovaries in women.

The name of most of the endocrine glands is known and quite distant from the medicine people at least once, briefly, but heard, but the mysterious word “paraganglia” many of the readers of this book (if not the vast majority) is clearly seen for the first time. Paraganglia (this name translated from Greek means “located near the nerve node) are clusters of cells in the nerve nodes and around large blood vessels.

Among the endocrine glands are glands that are at the same time as the glands of internal and external glands as are the excretory ducts and generate few secrets. These glands are called glands of mixed secretion. These include the pancreas, which produces hormones that enter the bloodstream, and digestive enzymes that enter the duodenum, as well as the sex glands. As endocrine glands, the sex glands produce sex hormones, and as glands of external secretion – sex cells (sperm and eggs).

And now answer this question – what is in any system, regardless of its purpose, affiliation and other factors?

Difficult to answer? Then here’s a hint – the word that is the correct answer begins with the letter “And”.

The hierarchy! Of course – hierarchy, the order of subordination of the lower links to the higher. According to the hierarchical principle of the endocrine glands are divided into main, which are called Central, and peripheral. The main ones are the hypothalamus, pineal gland and pituitary gland, which control the activity of all other, peripheral endocrine glands.

The endocrine system, as already mentioned, is one of the two main systems of our (and not only our) body. And the hypothalamus, pineal and pituitary gland – the master gland of this system. Figuratively, they can be called “cream of society” or “elite organs” of the body. With just one clarification. If the pituitary and pineal bodies are a separate gland, the hypothalamus is not the body, and a portion of the diencephalon.

Reading popular science books are comparable to the passage through the impenetrable thickets. Having met another obstacle, you need to take a machete or some other analogue of the ax and cut the way further. That is, having met something incomprehensible, you need to immediately get an explanation to continue reading with full understanding.

So, our brain consists of five parts – the anterior, formed by the large hemispheres, intermediate, middle, posterior and medulla. Long, medium, and diencephalon constitute the so-called “brain stem”, which is like a cap covered two hemispheres. The posterior brain includes parts called the cerebellum and the bridge.

In the hypothalamus there are more than 30 clusters of nerve cells called “hypothalamus nuclei”. These nerve cells are special. They differ from other colleagues, that is – nerve cells, the ability to produce special substances that stimulate or inhibit the production of hormones by the pituitary gland. “Stimulants” are called “liberins” (i.e. liberators) and “oppressors” are called statins (the name is derived from the Greek word “statos” meaning “stationary”). The hypothalamus is a link between the nervous and endocrine systems of the body. It combines the nervous and endocrine mechanisms of regulation into a single neuroendocrine system.

The pituitary gland, an endocrine gland located at the base of the brain, is the link between the hypothalamus and the rest of the endocrine glands. The pituitary gland is very small (its mass in an adult does not exceed a gram), but about it with full right you can say “small, Yes Udal”, because it is the pituitary gland that transmits “commands” from the hypothalamus to other glands.

If you compare the hypothalamus with the Supreme commander, the pituitary will be in the role of chief of the General staff.

Because of the “unbreakable” relationship with the hypothalamus pituitary gland is usually considered as a single hypothalamic-pituitary system, command or, if you want – the management of the endocrine system.

Due to the hormones that are produced in the pituitary gland, goes to tens. Among them are important hormones such as somatotropin or growth hormone, gonadotropins that stimulate the secretory activity of the gonads, vasopressin, which causes a reduction in blood vessels and increased blood pressure.

The pineal gland, also called the “pineal body” – is the youngest member of the governing endocrine triumvirate. The “pineal body,” the pineal gland called due to its ellipsoid shape resembling a fir-cone. Like the pituitary gland, the epiphysis is small – up to 1 cm in length.

Hormones produced by the pineal gland have a inhibitory effect on the development of the gonads and on the production of sex hormones. Also, epiphysis hormones affect the secretion of some hormones in the adrenal glands. The epiphysis produces the hormone melatonin, which regulates the activity of the body according to the daily rhythm. Actually, melatonin has several functions and one of them is the inhibition of the production of some pituitary hormones, for example – somatotropin. Thus, the younger member of the leading endocrine triumvirate – the pineal gland, affects the “superior” pituitary. There is a natural question – why is it so arranged, because the activity of the pituitary regulates the hypothalamus? Is it an accident or a certain regularity? In fact, nothing “random” in our body does not exist. In our body, everything is natural, logical and aimed at survival in an ever-changing environment. The essence of compensatory reactions (or, if you want – compensatory capabilities) of the body is that the function of damaged organs and systems take on other structures that are not affected by the action of the damaging agent. Therefore, many bodies have “understudies” that perform part of their functions. For example, the pineal body part “hedging” the hypothalamus.

The thyroid gland is located in the neck area below the larynx and in front of the trachea. This gland is shaped like a butterfly. In comparison with the pituitary gland and the epiphysis, the thyroid gland can be considered a “giant”, since its weight in an adult is from 15 to 25 g. the Giant is not a giant, but it is the largest endocrine gland. The pancreas, however, is larger than the thyroid, but it belongs to the glands of mixed secretion, and the thyroid is exclusively the endocrine gland.

The thyroid gland produces two hormones – thyroxine and triiodothyronine. In fact, not two, but only one, since triiodothyronine is the active form of thyroxine. This often happens – the hormone is first produced, and then activated, that is, dramatically increases its biochemical properties after joining the molecule or cleavage from it some atoms.

Triiodothyronine stimulates the growth and development of the body, regulates some metabolic processes. Molecules of thyroxine and triiodothyronine contain iodine atoms, so for the normal operation of the thyroid gland iodine is constantly required. An adult needs about 200 micrograms of iodine per day. With systematic iodine deficiency, thyroid function is inhibited and a condition (disease) called “hypothyroidism” develops [1]. In order to prevent hypothyroidism should be regularly eaten foods rich in iodine, such as feijoa, seaweed, sea fish, squid meat.

Parathyroid or parathyroid (“para-” in Greek means “about”) glands are four small, up to 5 mm in diameter, we can say – tiny, glands located behind the thyroid gland, two on each side. The parathyroid glands produce a parathyroid hormone that regulates calcium in the blood. Calcium is a very important chemical element for us. The level of calcium in the blood is important for the normal functioning of the nervous, cardiovascular and musculoskeletal systems of the body. With a systematic lack of calcium, muscle cramps occur, the rhythm of heartbeat is disrupted, bones become thinner and brittle, memory decreases.

The thymus (or thymus gland) is located at the top of the chest, just behind the sternum. The thymus consists of two parts, which can simply be adjacent to each other or connected by a jumper. The weight of the thymus of an adult is from 20 to 35 grams. The name “thymus” this iron was due to the fact that the form it resembles a fork with two teeth.

The thymus produces hormones responsible for the production of “T-lymphocytes” (thymus lymphocytes), one of the types of cells of the immune system, struggling with “invaders” – foreign agents that can harm the body. In violation of the function of the thymus, immunity decreases, because less T-lymphocytes are produced, and the fewer fighters, the weaker the army.

Adrenal glands are paired endocrine glands located, as the name implies, above the kidneys. The adrenal glands have the shape of an irregular prism and are small in size – the weight of the adrenal gland of an adult ranges from 8 to 12 grams.

The adrenal glands consist of an outer cortex and inner medulla.

Cortical cells produce several hormones with different functions. For example, hormones cortisone and cortisol stimulate the formation of glucose from fats and amino acids, inhibit inflammatory, immune and allergic reactions, increase the excitability of the nervous system. The hormone aldosterone regulates water-salt metabolism.

Cells of the adrenal medulla produce two very important hormones – adrenaline (a familiar name, right?) and noradrenaline, which create conditions for intense muscle work by increasing blood pressure, increased heart rate, increased blood glucose, expanding the lumen of the bronchi, etc. in Other words, adrenaline and noradrenaline increase the supply of muscle oxygen and glucose. Bronchi expand, increasing the flow of air into the lungs, therefore, increases the gas exchange between blood and air. Blood gets more oxygen from the air. It also increases the glucose content. Due to the increase in the number of heartbeats increases the flow to the organs of blood, rich in oxygen and glucose… Now you understand why under stressful situations, the production of adrenaline and norepinephrine increases dramatically? The body is preparing for action – to resist or to flee.

So we have come to a mysterious paraganglia, which, however, ceased to be for us mysterious.

The cells of these small ellipsoid formations (the length of the paraganglii of an adult does not exceed 8 mm) are similar in structure and function to the cells of the adrenal medulla. In paraganglia produces adrenaline and noradrenaline.

The pancreas, as already mentioned above, refers to glands with mixed secretion. Clusters of endocrine cells in the pancreas are called “islets of Langerhans” after the German scientist Paul Langerhans (1847-1888) who discovered them. Islets of Langerhans a great many. In an adult, their number reaches a million. These Islands produce several hormones, the most important of which are insulin (another familiar name) and glucagon.

Insulin and glucagon are antagonists, that is, they have the opposite effect. Glucagon increases blood glucose, and insulin lowers it. With insulin deficiency or in violation of the interaction with the target cells develops a serious disease – diabetes.

The Islet Of Langerhans. It can be seen that it is not connected to the system of pancreatic ducts, because it secretes directly into the blood.

Antagonists have most of the hormones. In such a complex system, what is our body, to regulate any function is not enough just a stimulant or only “oppressor” of this function. It is necessary that both the stimulant and the “oppressor”work at the same time. This “double” regulation is more stable, that is, more reliable and more accurate. And it also happens that some important function is regulated by a whole group of hormones.

Sex glands – male testicles and female ovaries produce male and female sex hormones. Male sex hormones are called androgens and female hormones are called estrogens. Do not think that only androgens are produced in the testicles, and only estrogens in the ovaries. Androgens and estrogens are produced in both men and women, but men produce more androgens than estrogens, and women – on the contrary.

The most “main”, that is – the most important of androgens is testosterone, which provides the development of primary and secondary male sexual characteristics, and also participates in the development of male germ cells – sperm. The most “main” of estrogens is estradiol, a female analogue of testosterone.

During pregnancy, the endocrine system is replenished by another organ – the placenta. The placenta produces hormones such as placental lactogen, very similar to growth hormone, chorionic gonadotropin, prolactin, estrogens, progesterone, cortisol.

Lactogen, gonadotropin, prolactin, progesterone, cortisol… do Not be afraid of incomprehensible and unusual names. Very soon they will become as familiar to you as, for example, the words “cloud” or “pavement”.

Familiarity with the endocrine system is over. Now you have an idea about the subject and will be able to answer this question – how is the endocrine system different from other systems? For example – from the respiratory and urinary, which are depicted in the figures.

All other systems are a conditional whole, a single structure, and the organs and cells of the endocrine system are scattered throughout the body. That’s the difference. The endocrine system is United by blood, in which all cells secrete their products.

Reading this book can be alternated with reading the fantastic novel by Alexander Belyaev “the Man who lost his face”, which describes the application of the achievements of endocrinology to change the human body. Just read it “the Man who lost his face” and not its revised version called “the Man who found his face.” The revised version is not so exciting and highly ideologized.

Ninety years have passed since the writing of “the Man who lost his face”. You will be interested to know what the dreamers saw endocrinology at the dawn of its development and what problems they hoped to solve with its help. But while reading, be aware that you are reading a fantastic novel. About the real state of Affairs in endocrinology will tell you a book that you are now holding in your hands.

Officially, the year of the birth of the science of endocrinology is considered to be 1848, the British physician Thomas Addison began to study the deadly disease, which was later named after him. But the real date of birth of endocrinology should be considered 1905, in which the British physiologists William Bailey and Ernst Starling introduced the concept of “hormone”. Without this concept, endocrinology could not be considered a full-fledged scientific discipline, since any science must necessarily have a concept of its subject. The object of endocrinology is the endocrine system, and the subject – hormones, invisible to the eye “intermediaries” that control the processes occurring in our body.

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