The endocrine system is one of the ways to communicate within the human body. It consists of a group of cells that secrete chemicals called hormones.
The human body contains many hormones that regulate the various
functions of the body. Hormones are known as body chemicals produced by the endocrine glands, which include pituitary glands, adrenal glands, thyroid glands, thymus, and pancreas.
Hormones are characterized by secretion at some particular place in the body, but they work far away from this place, but some hormones also affect nearby the place of secretion.
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| Glands in the Endocrine System and Mechanism of Hormone Action |
Endocrine
System and Mechanism of Hormone Action: Understanding Hormone Receptors
What is the Endocrine System?
The
endocrine system is one of the ways to communicate within the human body.
The
endocrine system consists of a group of cells that secrete chemicals called
hormones, which in turn travel through the bloodstream and then bind to special
receptors on the target cells.
In fact, the
endocrine system is called this name because the endocrine glands do not have channels
in which their secretions are excreted, unlike the Sebaceous glands and the
sweat glands that make up the so-called exocrine system.
While the
endocrine glands secrete their hormones directly into the surrounding fluids,
they then travel through the interstitial fluid into the blood vessels.
It is
worth noting that endocrine hormones work to regulate many vital functions in
the human body, the most prominent of which are: growth, metabolism, sexual
development, etc.
What are Hormones?
Hormones can
be defined as chemicals secreted by certain organs of the body known as glands,
and are classified into a device known as the endocrine system.
In fact, the
principle in the presence of hormones is to achieve communication among
membranes. These hormones are released into the bloodstream, and the
bloodstream is transferred to the organs or tissues involved.
Once the
hormone is reached, a series of reactions occur within the organ or tissue. It
is important to note that the hormones are very powerful chemicals, they are
not only released by the glands found in humans but also there are hormones in
plants and animals and help each of them to perform the functions of the body
correctly and accurately.
Read also: Hormone Interactions with Target Cells
What are the Two Mechanisms of Hormone Action?
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| Mechanism of hormone action |
Mechanism of Hormone Action
Hormones are
divided in terms of their effect on the cell into two
main types:
(1)
Hormones with cell surface receptors: They work through receptors on the cell membrane (surface
receptors) without entering the cell cytoplasm, such as peptide hormones,
protein hormones, epinephrine hormones, prostaglandins.
(2)
Hormones with intracellular receptors: They work through entering the center of the cell and its
association with the receptors within the cytoplasm, for example, steroids,
thyroid hormones, and vitamin D3.
Hormones with cell surface
receptors:
A number of
protein hormones and multiple bonds, as well as the hormone norepinephrine and
prostaglandins function, and its direct impact on the surface receptors through the so-called
second messenger system or cyclic adenosine monophosphate (C-AMP), after a
series of enzymatic reactions produced at the end of which a special type of
protein or enzyme is invaded by the body as a by-product due to the effect of
the secreted hormone and by the type of receptor.
Therefore,
the effect of the hormone on the cell depends mainly on the type of receptor
located on the surface of the membrane where these receptors are strictly
specialized and receive only the hormone.
The
connector usually consists of 3 protein components: the receptor, the helper
and the vector.
When the
hormone reaches its receptor on the outer surface of the membrane, the action
of the hormone ends and the catalyst is stimulated.
In this
case, the adenylate cyclase is on the inner end of the membrane. This enzyme
activates the transformation of adenosine triphosphate (ATP).
Adenosine
triphosphate into cyclic adenosine monophosphate ring (C-AMP) changes the state
of protein from an inactive to an active state.
These
receptors originate from integral proteins and are usually located on one of
three extracellular sites on the external membrane surface, transmembrane or on
the tip of the membrane from the inside (Cytoplasmic).
The second
connector theory of protein hormones can be summarized as follows:
The hormone
(first connector) binds to its own receptor on the outer surface of the cell
membrane.
ATP is
converted to C-AMP by the direct effect of adenylate cyclase in the presence of
calcium ions and guanosine triphosphate (GTP). C-AMP as a second agent
stimulates internal reactions that result in protein kinase synthesis (PKA).
The increase
in CAMP results in the formation of more PKA and its receptor changes from an
inactive state to an active state.
When PKA
becomes active it can add a phosphorylation group to a number of proteins
within the cell that may include enzymes needed by the body in response to the
effect of the secreted hormone or special protein needed in its growth.
Hormones with Intracellular Receptors
Hormones
with cytoplasmic receptors inside the cell: Examples of hormones
that function in this way are fatty hormones as well as thyroid hormones and
vitamin D3. They can be summarized as follows:
The
cytoplasm enters through the cell membranes and is associated
with special receptors within the cytoplasm or on the membrane of the nucleus,
resulting in a chemical compound between the hormone and receptor (hormone
receptor).
The hormone
moves in its receptors into the nucleus. This results in the transcription of
special genes consisting of messenger-ribonucleic acid (m-RNA).
The mRNA
synthesized into the cytoplasm moves to stimulate the formation of new proteins
on the coarse endoplasmic network. These proteins may be enzymes needed by
cells to perform a specific function, or new proteins that the cell may need in
its growth and development.
In both
cases, whether the hormone function through the receptor on the outer membrane
of the cell (proteins) or inside the cell (lipids), the hormone may have a
number of receptors of its own, but the response may vary depending on the
target member and the type of receptor it carries.
Summary
There are
many types of glands that secrete hormones such as the pituitary gland,
hypothalamus, adrenal gland, thyroid gland, pineal gland, thymus gland, sex
steroids, etc.
Hormones are
divided in terms of their effect on the cell into two main types:
A. Hormones
with cell surface receptors
B - Hormones
with cytoplasmic receptors inside the cell
Hormone
receptors play a vital role in the mechanism of hormone action. The hormone
affects the target tissue by activating the target hormone receptors in the
tissue cells; then it changes the function of the hormone receptors, so this
receptor is the direct cause of the hormone effects.
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