The endocrine system is a complex system of organs that work together to release any chemical messengers located inside our body called hormones. The endocrine system works in coordination with the nervous system to regulate different body functions such as metabolism, growth, and reproduction hormones secreted by endocrine glands that together make up the endocrine system.

The endocrine glands are also called ductless glands because they do not have any ducts and therefore their secretions are called hormones in the bloodstream vessels, through which they reach the organs the hormones flow inside the bloodstream. Blood carries hormones to the needed sites where they carry the further process.

Types of Hormones

To regulate various functions, different types of hormones are produced in the body. They are classified as follows:

Peptide Hormones
Steroid Hormones
Peptide Hormones

What Is The Mechanism of Hormone Action?

A hormone is a chemical messenger secreted to enable communication between cells and tissues throughout the body. They flow through the bloodline. The mechanism of hormone action begins at the endocrine system. A hormone action regulates various other systems including the excretory and reproductive systems.

Hormone action activities exit their respective cells of origin by the means of membrane transport. Hormones are chemical messengers of the human body that affect different tissues of the human body. The site of the hormone action is usually far away from its site of origin. In the human body, there are numerous hormones performing various functions for different purposes.

What Is The Mechanism of Peptide Hormone Action?

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Peptide hormones find their functional value in the plasma membrane of different target cells. The hormone action of peptide hormones is the so-called second messenger function that takes place within the cell. The mechanism of peptide hormone action leads to the generation of secondary messenger hormones. These secondary messengers are also similar to hormones that are chemical messengers. The structure of the cell surface receptors has three underlying domains that form an integral part of the membrane structure of the proteins. The three structural domains are namely:

Extracellular domain
Transmembrane domain
Intracellular domain

Except for the receptors of the thyroid hormone, all other amino acid receptors and peptide hormones are located in the plasma membrane. At the target cells, the hormones undergo various unique biological activities.

Hormonal Imbalance in the Human Body

Hormonal imbalance in the human body is caused due to several health conditions. Some major diseases caused by hormonal dis functionalities are diabetes, thyroid disorders, polycystic ovary syndrome (PCOS), and various other menstrual syndromes. Ovarian tumors and ovarian cysts are common conditions caused as a result of excess Androgen in the human body.

Endocrine Glands and the Hormones Secretion

As stated before, hormones are released by the endocrine glands. These are very different from other glands of the human body.

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The Different Hormones Performing Different Functions are as follows:

Thyroid: Heartbeat regulation and maintains calorie intake.
Pancreas: produces insulin and regulates blood sugar level.
Ovaries: The ovaries secrete sex hormones that are essential for reproductive cycles. Pituitary Gland: The pituitary gland is the major hormone-releasing organ of the body. The gland releases all of the major hormones of the human body.
Adrenal Gland: The adrenal gland releases stress hormones. There are two mechanisms of hormone action that are required for the proper functioning of the human body.

Feedback Mechanism – Thyroid

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The thyroid gland produces a hormone called thyroxine. When the level of thyroxine in the blood reduces, the hypothalamus stimulates thyroxine secretion by stimulating TSH secretion. This represents a positive feedback mechanism.

If the hypothalamus continues to produce thyroxine, blood levels of thyroxine can increase. This sends negative feedback to the hypothalamus. Hormones are aimed at specific functions of the target tissue. It will be eliminated when you arrive at your destination.

Solved Examples

Explain the Two Mechanisms of Hormone Action in The Human Body.

The two mechanisms of hormone action in the human body are broadly divided into two groups:

Mobile receptor mechanism
Fixed membrane mechanism
Mobile Receptor Mechanism: In this form of hormone action the steroids and fatty acids can pass through the lipid membranes easily. The hormones bind to the target receptor and enzymatic activates.
Fixed Membrane Mechanism: In the fixed membrane mechanism the hormones can’t pass through the lipid membranes. This type of mechanism is generally shown by water-soluble hormones such as amines or proteins.

What are The Features of Hormones?

Hormones are the chemical messengers of the human body. Different hormones have different effects on the functioning of the human body. The hormones help in the growth, metabolism, development, reproduction, and secretion of fluids. The mechanism of hormone action will start at a certain time and keep working over a continuous period of time. A few important hormones of the human body are Insulin, thyroid hormones, estrogen, progesterone, testosterone, and serotonin.

Functions of Hormones

Following are some important functions of hormones:

Food metabolism.
Growth and development.
Controlling thirst and hunger.
Maintaining body temperature.
Regulating mood and cognitive functions.
Initiating and maintaining sexual development and reproduction

Fun Facts About The Hormone Action In The Human Body

Although estrogen is a female or one and testosterone is a male hormone, both male and female bodies need these two hormones.
The hormone action in the human body performs the following functions. Progesterone helps maintain body balance.
Our memory, learning, and motor control activities need testosterone and estrogen.
Women become hormonal during their menstrual cycle as the rate of secretion of progesterone increases during a very short span.
Oxytocin is an essential hormone and is important during childbirth.

Conclusion

This is all about hormones, their sources - endocrine glands, and their functions. Learn how these biochemical compounds hold their importance in human physiological functions. Concentrate on how the hormones act on the different organs and tissues of a human body to promote another function.

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FAQs on Mechanism of Hormone Action: Processes and Examples

1. What is the basic mechanism of hormone action in the human body?

The basic mechanism of hormone action begins when a hormone, circulating in the bloodstream, binds to a specific protein called a hormone receptor. These receptors are located either on the surface or inside target cells. This binding forms a hormone-receptor complex, which is the crucial first step that triggers a series of biochemical changes within the cell, ultimately leading to a specific physiological response or change in function.

2. How are hormones classified based on their chemical nature?

Based on their chemical structure, hormones are classified into four main types, which is important as their nature determines their mechanism of action:

Peptide/Polypeptide Hormones: These are made of amino acid chains. Examples include insulin, glucagon, and pituitary hormones.
Steroid Hormones: These are derived from cholesterol. Examples include cortisol, testosterone, and estrogen.
Iodothyronines: These are derived from the amino acid tyrosine and iodine. An example is the thyroid hormones (T3 and T4).
Amino-acid derivatives: These are modified from single amino acids. An example is adrenaline (epinephrine).

3. Can you explain the mechanism of action for a protein hormone like insulin?

A protein hormone like insulin is not lipid-soluble, so it cannot enter the target cell. Instead, its mechanism involves these steps:

It binds to a specific membrane-bound receptor on the cell's surface.
This binding activates the receptor, which in turn generates second messengers inside the cell (e.g., cyclic AMP, Ca++, or IP3).
These second messengers trigger an intracellular cascade of biochemical reactions.
This cascade amplifies the signal and leads to the physiological response, such as increased glucose uptake by the cell.

4. What is the mechanism of action for a steroid hormone like cortisol?

Steroid hormones like cortisol are lipid-soluble and can pass directly through the cell membrane. Their mechanism is as follows:

The hormone diffuses across the cell membrane and binds to an intracellular receptor, located in the cytoplasm or nucleus.
The resulting hormone-receptor complex moves into the nucleus and binds to a specific segment of DNA.
This binding directly influences gene expression, by either activating or inhibiting the transcription of specific genes into mRNA.
The change in protein synthesis alters the cell's metabolism and function, producing a physiological response.

5. What is the key difference between the mechanism of action for membrane-bound and intracellular receptors?

The key difference lies in their location and the type of hormone they interact with. Membrane-bound receptors are located on the cell surface and bind to water-soluble hormones (like peptides) that cannot enter the cell; their action is rapid and mediated by second messengers. In contrast, intracellular receptors are inside the cell and bind to lipid-soluble hormones (like steroids) that can pass through the membrane; their action involves directly changing gene expression, which is typically slower but more long-lasting.

6. Why can steroid hormones pass through the cell membrane while peptide hormones cannot?

This is due to the chemical compatibility between the hormone and the cell membrane. The cell membrane is a lipid bilayer, meaning it is made of fats. Steroid hormones are also lipid-based (lipophilic), allowing them to dissolve in and easily pass through this membrane. Peptide hormones, on the other hand, are protein-based and water-soluble (lipophobic). Their chemical nature prevents them from passing through the fatty membrane, so they must bind to receptors on the outside of the cell.

7. How does a single hormone like adrenaline cause different effects in different body tissues?

A single hormone can trigger different responses because the effect is determined by the type of receptor in the target tissue, not just the hormone itself. For example, adrenaline causes the heart muscle to contract more forcefully by binding to β1 receptors. In contrast, it causes the airways in the lungs to relax by binding to β2 receptors. The hormone is the same, but the different receptors in various tissues initiate unique intracellular signaling pathways, leading to distinct physiological outcomes.

8. What is a hormone-receptor complex, and why is its formation so important for hormone action?

A hormone-receptor complex is the structure formed when a hormone molecule binds specifically and reversibly to its receptor protein. The formation of this complex is the single most important event in hormone action because it is the trigger for all subsequent cellular responses. It ensures specificity, meaning a hormone will only affect cells that have the correct receptor. Without the formation of this complex, a hormone cannot deliver its chemical message, and no physiological effect will occur.

9. What are second messengers and what is their primary role in hormone action?

Second messengers are small, non-protein intracellular molecules that are generated when a hormone (the 'first messenger') binds to a membrane receptor. Their primary role is to amplify the hormonal signal and transmit it from the cell surface to internal cellular machinery. A single hormone-receptor complex can lead to the generation of many second messenger molecules, creating a powerful cascade that results in a significant and rapid cellular response. Common examples include cyclic AMP (cAMP), Inositol triphosphate (IP3), and Calcium ions (Ca++).

10. How exactly do hormones regulate gene expression?

Hormones, primarily steroid and thyroid hormones, regulate gene expression by interacting directly with the cell's genetic material. After forming a complex with an intracellular receptor, the complex travels to the nucleus. Here, it binds to a specific DNA sequence known as a Hormone Response Element (HRE), which is located near the gene the hormone controls. This binding acts like a switch, either promoting or inhibiting the transcription of that gene into messenger RNA (mRNA). This change in mRNA production alters the rate of synthesis of specific proteins, which then carry out the final physiological function.