Articles, Blog

Mechanisms of Hormone Action

October 10, 2019

The endocrine system is a very important
and very involved system within our bodies. It allows our body to communicate over
long distances and is a major player in regulating a
stable environment or in other words preserving homeostasis. This system employs the use of hormones which are chemicals secreted from glands
and enter the bloodstream where they circulate until exerting an
effect on a downstream target cell. We’re going to be specifically talking
about the two types of mechanisms in which hormones exert their effect on
target cells. But to start off here’s a brief overview what hormones
are and how they work. There are three basic group of hormones. 1. Amino acid derivatives. 2. Peptide hormones and 3. Lipid derivatives or steroid hormones.
For amino acid derivatives, these are small molecules and they come
from amino acids like tyrosine and tryptophan. One hormone derived from tryptophan is melatonin. A hormone involved in our
sleep-wake cycles. You can get tryptophan from foods like
turkey, chocolate or milk. Peptide hormones are made up of a bunch of amino acids. Some examples would
be thyroid-stimulating hormone, oxytocin or
prolactin. Lipid derivatives or steroid hormones are
considered lipophilic meaning they have an affinity for lipid
structures which we’ll take a look at shortly. They circulate in the blood bound to
carrier proteins so they usually last in the circulation
longer than other types of hormones. There are two main mechanisms for which a hormone can affect a target
cell. The first is by and non steroid action. This
mechanism is employed by an amino acid hormone or a
peptide hormone. These hormones cannot freely cross a
membrane on a target cell so it first acts by binding a cell surface
receptor. There is then an intracellular
signaling cascade that occurs in order for the desired effect to take place. There are proteins on the intracellular side
of the target cell that are associated with the receptor.
Most often this involves what’s called a G-protein.
This G protein is found next to an enzyme that converts ATP to a molecule called cyclic AMP or cAMP. This is something that makes
this mechanism unique. Cyclic AMP is called a second
messenger because it signals a cascade of events
that eventually change the enzymatic activity in a cell
to cause the target cell response. Examples of hormones that use the cyclic
AMP second messenger system include ACTH, calcitonin, epinephrine, glucagon, parathyroid hormone and ADH. The second mechanism is the steroid action. Because lipid derivative or steroid
hormones are lipophilic they can freely move through the
membrane and into the cell. From there they can either bind to a
receptor within the cell or they can move freely into the nucleus
where the hormone or hormone complex causes a change in
gene activity. This then increases transcription and mRNA production which then leads to
an increase in protein production within the cell. Examples of hormones that
exert effects via steroid hormone mechanisms are testosterone, estrogen, progesterone, aldosterone, and calcitriol.

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  • Reply Rebekah W. July 22, 2015 at 7:45 pm

    Very clearly explained. Thank you.

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    thank u..its so clear

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    thanks very clear and straight forward

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  • Reply Carmen Lee April 30, 2016 at 3:54 pm

    Thank u!!

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    can any one tell me which mechanism is faster.

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    super sir

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    I just wanted mechanisms of water and lipid soluble harmone action

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  • Reply Mridupawan Borpatra Gohain March 25, 2019 at 1:02 pm

    Thank you for simplified explanation

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