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Lecture No 1.
Endocrinology
(Introduction)
Prepared of prof.L.Bobyreva
• Endocrinology is a science, which comprises the study
the development, the structure and the functions of
endocrine glands, biosynthesis, the mechanism of action
and hormones metabolism in the organism, secretion of
these hormones in norm and during dysfunction of
endocrine glands, and the diseases of endocrine system.
• The glands of internal secretion produce hormones and
release them into the blood. These hormones have definite
influence on the metabolism changing the function of the
whole organism or separate organs and systems. Thus, the
major object of endocrine system is the functioning
coordination of organs and systems. It is realized in close
interaction with the central nervous system. Therefore it is
more correct to say about a neuroendocrine regulation and
neuroendocrine system of the human organism.
epiphysis
hypophysis
thyroid gland
thymus
Parathyroid glands
thyroid
gland
adrenal
cortex
adrenal
gland
adrenal
medulla
pancreas
Langergans islet
ovaries
testicles
ovaries
Parathy-roid
glands
The endocrine
system is composed
of:
hypophysis (pituitary
gland),
thyroid gland,
parathyroid glands,
insular apparatus of
pancreas,
adrenal medulla and
adrenal cortex,
testicles,
ovaries,
epiphysis,
and thymus.
• Functional activity of endocrine system depends
•
•
•
on:
ability of endocrine glands to produce the
necessary amount of hormones;
a state of target tissues. Target tissue is a tissue,
which is sensitive to the action of definite
hormone and having specific biological effect on
this action. The ability of target tissues to react
to the corresponding hormone is determined by
the presence of receptors, which interact with
this hormone.
The endocrine function of an organism is
provided with systems, which include:
• endocrine glands secreting hormones;
• hormones and different ways of their transport;
• proper organs and target tissues, responding to action of
hormones.
At present there are following variants of hormones' action:
• hormonal, i.e. the action on long distance from the place of
forming;
• isocrinal (local) action, when the chemical agent synthesized
in one cell, to have an effect on the cell which is located in
close contact with the first one. Releasing of this agent occurs
into intertissue liquid or blood;
• neurocrinal (neuroendocrinal) action, when hormone during
releasing from nerve endings functions as neurotransmitter or
neuromodulator , i.e. hormone acts as a substance which
changes (usually intensifying) the action of neurotransmitter;
• paracrinal action is the type of the isocrinal action but
hormone forming in one cell enters into intertissue liquid and
has an influence on some cells, located near it;
• autocrinal action, when hormone releasing from the cell has
definite influence on the same cell, changing its functional
activity .
Depending on the chemical composition, hormones
are divided into:
• albuminous (protein) hormones are
adrenocorticotropic hormone (ACTH),
somatotrophic hormone, melano-stimulating
hormone (MSH), prolactin, parathyroid hormone,
calcitonin, insulin, glucagon, thyrotropic
hormone (thyroid-stimulating hormone) (TSH),
follicle-stimulating hormone, luteinizing
(interstitial cell-stimulating) hormone (ICSH),
and tyroglobulin;
• steriod (or lipidic) hormones are corticosterone,
cortisol, aldosterone, progesterone, estradiol,
estrone, estriol, testosterone;
• amino acid derived hormones are adrenalin,
noradrenaline (norepinephrine), thyroid
hormones (triiodothyronine, tetraiodthyroxin).
Hormones realize their biological action
combining with receptors. Receptors are
informational molecules, which transform
the hormonal signal into hormonal
activity. At present there are
approximately 60 hormonal receptors.
More than half of them are localized on
the cell membranes. These are receptors
to peptide hormones. Steroid hormones
and amino acid derived hormones
interact with receptors located
intercellular (cytoplasmic and nuclear).
R
Influence to
membrane
(transport)
Inactive
protein kinase
H
cAMP
АC
H
Active
protein kinase
R
АМP
Synthesis
of
proteine
Resulting
biological
effect
Activation
of enzymes
Membrane
Mechanism of protein hormone action by force of cAMP activation:
R- receptor, H – hormone, AC - adenylate cyclase.
Са+protein
H
H
Active calmodulin
Inactive calmodulin
R
Ca2+
Activation
Kinase
phosphorylase
s
Ca2+
RР
Resulting biological
effect
Membrane
Mechanism of protein hormone action by force of Са2+.
R – receptor; H – hormone.
Ca2+
Biological effect of
hormones interacting with
receptors, localized on a
plasmatic membrane,
realizes with the
collaboration of "secondary
messenger":
cyclic adenosine
monophosphate (adenosine
phosphoric acid) (AMP) –
adrenocorticotropic
hormone (ACTH), thyroidstimulating hormone
(thyrothropin, TSH), folliclestimulating hormone (FSH),
luteinizing hormone,
melano-stimulating
hormone (MSH),
vasopressin (antidiuretic
hormone), parathyroid
hormone, adrenalin and
others;
ionized calcium (Ca++)
– oxytocin, noradrenaline
(norepinephrine) and
others;
"secondary
messenger" is unknown –
somatotrophic hormone,
prolactin (lactotropin),
insulin and others .