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Endocrine glands (from the Greek endon - inside, crio - secrete) or endocrine
glands are specialized organs or groups of cells, the main function of which is to
produce and release specific biologically active substances into the internal
environment of the body
...
Their
cells are intertwined with an abundant network of blood and lymphatic vessels,
and waste products are released directly into the blood, lymph, and tissue fluid
...

The products produced by the endocrine glands are called hormones (Greek
hormao - excite, activate)
...
Bernard, and the term “hormone” by the English
physiologists W
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Starling in 1902
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Hormones are
formed in glandular endocrine cells, after which they enter the internal
environment, mainly into the blood and lymph
...

High biological activity
...
Thus, the concentration of the female sex hormone (estradiol) in
the blood ranges from 0
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6 mcg (10-6 g) per 100 ml of plasma
...
The pituitary gland reacts to picograms (10-12 g) of
hypothalamic hormones, angiotensin-P, a product of endocrine cells of the
kidneys, causes a feeling of thirst in femtograms (10-15 g)
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Specificity
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In this regard, the deficiency of any
hormone cannot be compensated for by other hormones or biologically active
substances
...
Hormones, as a rule, are transported in the blood far from the
site of formation, affecting distant organs and tissues
...

Chemical structure of hormones and their transformation in the body
According to their chemical structure, hormones can be divided into 4 main
groups:
proteins and peptides;
amino acid derivatives;
steroids;
prostaglandins
...
Some of them (follitropin,
thyrotropin, lutropin) are complex proteins, others (insulin, calcitonin, etc
...
Glucagon, vasopressin, oxytocin, and hypothalamic hormones
have a peptide structure
...
Steroid
hormones are based on the cyclic hydrocarbon core
cyclopentaneperhydrophenanthrene
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The main stages of hormone formation and transformation can be represented as
follows:
hormone biosynthesis;
secretion, i
...
isolation from an endocrine cell;
transport by blood to peripheral tissues;
recognition of a hormonal signal by target cells;
transduction (translation) of a hormonal signal into a biological response;
suppression of the hormonal signal
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Organs and tissues
Cells
Hormones
1
...


Thymus
Thymocytes
Thymosin, thymopoietin
3
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Heart
Atrial myocytes
Atriopeptide, somatostatin, angiotensin-P
Organs, tissues and cells with endocrine function
No
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Hypothalamus
Nerve cells of punctate structures
Hypothalamic neurohormones:
Posterior hypothalamus
Nerve cells of the magnocellular nuclei of the anterior hypothalamus
a) liberins: corticoliberin, thyroliberin, luliberin, folliberin, somatoliberin,
prolactoliberin, melanoliberin;
b) statins: prolactostatin, melanostatin, somatostatin
Vasopressin, oxytocin
2
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Adrenal glands Cortex
Brain matter
Zona glomerulosa Zona fasciculata Zona reticularis
Chromaffin cells
Mineralocorticoids Glucocorticoids Sex steroids: androgens, estrogens
Adrenaline, norepinephrinelin
4
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Parathyroid glands
Chief cells K cells
Parathyrin Calcitonin
6
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Pancreas
Islets of Langerhans:
os-cells P-cells A-cells
Glucagon
Insulin
Somatostatin
8
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Consequently, it depends on the structure and
expression of the genes encoding the synthesis of these hormones, as well as on
the enzymes that regulate hormone synthesis and post-translational processes
...
An
example is dwarfism due to a genetic defect in growth hormone
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Secretion of hormones
...
The hormone packaged in vesicles or granules is
transported towards the cytoplasmic membrane
...
After this,
their lysis occurs and the hormone leaves the cell
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Hormone secretion is an act accompanied by energy expenditure, so it is always
associated with shifts in the ATP-cAMP system
...
Therefore, a decrease in the content of
calcium ions in the extracellular environment and its entry into the endocrine cell
inevitably leads to a decrease in the secretory activity of this cell
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Transport of hormones
...
Most hormones
form complex compounds in the blood with plasma proteins
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Complexation with proteins is a reversible process
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The formation of a bound form of hormones is of great physiological importance
...
Secondly, the bound form of the
hormone is its physiological reserve
...
e
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Finally, complexation
with proteins prevents the filtration of small-molecule hormones through the
glomeruli and thereby inhibits these important regulatory processes
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Recognition of a hormonal signal
...
During the peripheral action of hormones, various transformations occur
...
Thus,
the thyroid hormone thyroxine can be converted in tissues into triiodothyronine,
a more active hormone of the same gland
...

Transduction of a hormonal signal into a biological response is organically related
to the mechanism of action of this hormone
...
This phenomenon is called hormone reception,
and the cellular components that interact with the hormone are called receptors
...

The structure of the receptor molecule is characterized by asymmetry
...
e
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Receptors are located either intracellularly or on the surface of the cytoplasmic
membrane
...
It is also believed that the function of recognizing
a specific hormonal signal in all cells for all hormones is carried out by a
membrane receptor, and after binding of a hormone to its corresponding
receptor, the further role of the hormone-receptor complex for peptide and
steroid hormones is different In peptide, protein hormones and catecholamines,
the hormone-receptor complex leads to the activation of membrane enzymes and
the formation of various secondary messengers (messengers) of the hormonal
regulatory effect, which realize their action in the cytoplasm, organelles and cell
nucleus
...

4
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The adenylate cyclase - cAMP system
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Activation of
adenylate cyclase occurs under the influence of a hormone-receptor complex, the
formation of which leads to the binding of guanyl nucleotide (GTP) to a special
regulatory stimulating protein (GS protein), after which the GS protein causes the
addition of magnesium to adenylate cyclase and its activation
...
Some hormones, on the contrary, suppress
adenylate cyclase (somatostatin, angiotensin-P, etc
...
This changes the
permeability of membranes, i
...
causes metabolic and, accordingly, functional

changes typical for the hormone
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"Guanylate cyclase - cGMP" system
...
This is how
atrial natriuretic hormone, atriopeptide, a tissue hormone of the vascular wall,
realizes its effects
...
Examples include stimulation of cardiac
contractions under the influence of cAMP and inhibition of them by cGMP,
stimulation of contractions of intestinal smooth muscles by cGMP and inhibition
of cAMP
...
3 Phospholipase C - isositol triphosphate system
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Iositol triphosphate causes the release of
ionized calcium from intracellular stores
...
Diacylglycerol also activates and
completes the process of phosphorylation of other proteins, while simultaneously
implementing the second pathway of hormonal effect: through the formation of
arachidonic acid, which is a source of substances with powerful metabolic and
physiological effects - prostaglandins and leukotrienes
...

4
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The calcium-calmodulin system
...
In the cytoplasm of non-muscle cells, calcium binds to
a special protein - calmodulin, and in muscle cells the role of calmodulin is played
by troponin C
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A short-term increase in the amount of
calcium in the cell and its binding to calmodulin is a stimulus for numerous
physiological processes - muscle contraction, secretion of hormones and release
of mediators, DNA synthesis, changes in cell motility, enzyme activity, transport of

substances through membranes
...
In the
cytoplasm there is a special cytoplasmic receptor protein with which the hormone
binds
...
All these phenomena require the long-term presence of the hormonereceptor complex in the nucleus
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These are effects such as increased pmembrane permeability, increased
transport of glucose and amino acids, release of lysosomal enzymes, shifts in
mitochondrial energy and, in addition, an increase in cAMP and ionized calcium
...

Peptide hormones also have the ability to selectively influence gene transcription
in the cell nucleus
...

The phenomenon of internalization of hormone-receptor complexes and thereby
reducing the number of hormone receptors on the cell membrane allows us to
understand the mechanism of decreased effector sensitivity with an excess
amount of hormonal molecules, or the phenomenon of effector desensitization
...

The opposite phenomenon - sensitization, or increased sensitivity to hormones,
can be caused by an increase in the number of free receptor sites on the
membrane, both due to a decrease in internalization and as a result of the
“floating up” of active receptor binding sites
...

5
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There are 5 types
of effects of hormones on target tissues: metabolic, morphogenetic, kinetic,
corrective, reactogenic
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Metabolic shifts caused by hormones underlie changes in cell,
tissue, and organ function
...

Examples include the influence of somatotropin on the growth of the body and
internal organs, the influence of sex hormones on the development of secondary
sexual characteristics
...
For
example, oxytocin causes contraction of the uterine muscles, adrenaline triggers
the breakdown of glycogen in the liver and the release of glucose into the blood,
vysopressin activates the mechanism for the reabsorption of water in the
collecting ducts of the nephrons
...
Examples of the
corrective effect of hormones are the effect of adrenaline on heart rate,
activation of oxidative processes by thyroxine, and a decrease in the reabsorption
of potassium ions in the kidneys under the influence of aldosterone
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For example, when the
anabolic processes of protein metabolism initially predominate, glucocorticoids
cause a catabolic effect, but if protein breakdown initially predominates,
glucocorticoids stimulate their synthesis
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For example, thyroid hormones
enhance the effects of catecholamines, calcium-regulating hormones reduce the
sensitivity of the distal nephron to the action of vasopressin
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For example, glucocorticoids have a permissive effect in relation to
catecholamines (the presence of small amounts of cortisol is necessary for the
effects of adrenaline to occur); insulin has a permissive effect in relation to
somatotropin, etc
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Extinguishing the hormonal signal
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There are numerous mechanisms for dampening the hormonal signal
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Along with this, destruction (catabolism) of
part of the released hormones occurs
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Liver enzymes inactivate hormones through deamination and methylation
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Some free and conjugated hormones enter the bile and are excreted from the
body through the intestines
...
In some cases, antibodies to hormones and other
inhibitors are for

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