Endocrine System and Mechanism of Hormone Action: Understanding Hormone Receptors

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.
Mechanism of hormone action
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.

What are the Two Mechanisms of Hormone Action? 

Mechanism of Hormone Action
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 cellExamples 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.

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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