Mechanism Of Hormone Action- Overview, Function & Regulation

Mechanism Of Hormone Action: Overview, Functions

Edited By Irshad Anwar | Updated on Jul 02, 2025 06:50 PM IST

The mechanism of hormone action explains how hormones interact with target cells to regulate various biological processes. Hormones bind to specific receptors on or inside the cells, triggering a series of events that influence cell function. This process can involve changes in gene expression, enzyme activity, or cell signalling pathways. In this article, hormones, receptors and their locations, classification of hormones, mechanisms of hormone action, hormones as regulators, hormones as messengers, signalling pathways, steroid and thyroid hormones, examples of hormone action, regulation of hormonal activity, and hormonal synergism and antagonism are discussed. Mechanism of hormone action is a topic of the chapter Chemical Coordination and Integration chapter of Biology.

This Story also Contains

Definition of Hormones
Receptors and their Locations
Classification of Hormones
Mechanisms of Hormone Action
Hormones As Regulators
Hormones As Messengers
Signaling Pathways
Steroid and Thyroid Hormones
Examples Of Hormone Action
Regulation of Hormonal Activity
Hormonal Synergism And Antagonism

Mechanism Of Hormone Action: Overview, Functions

Definition of Hormones

A hormone is a small chemical messenger that travels in the blood to help maintain internal balance or homeostasis in the human body. The definition only scratches the surface, as hormones play roles in many complicated functions within varied systems.

Receptors and their Locations

Hormones work through specific receptors, and sensitivity and responsiveness depend on the number of receptors along with their affinity for the hormone. Receptors are located in various sites, such as:

At the Cell Membrane:

Example: Protein or peptide hormones, and also catecholamines, act through receptors on the cell membrane.

Inside the Cytoplasm:

Example: Steroid hormones bind to receptors inside the cytoplasm.

In the Cell Nucleus:

For example, thyroxine acts on receptors in the nucleus.

Classification of Hormones

The hormones are classified based on their chemical nature:

Peptide, Polypeptide, and Protein Hormones: Examples are insulin and growth hormone.

Steroids:

Examples are cortisol and estrogen.

Steroid hormone action

Iodothyronines:

Examples are thyroxine and triiodothyronine.

Amino Acid Derivatives:

Examples are epinephrine and norepinephrine.

Generally, hormones acting through membrane-bound receptors do not directly enter the target cells. On the contrary, they form second messengers that act to control cellular metabolism. In contrast, hormones acting through intracellular receptors most often work by regulating gene expression or chromosome function by the interaction of hormone-receptor complexes with the genome. All these biochemical effects ultimately lead to physiological and developmental responses.

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Mechanisms of Hormone Action

The mechanism of action of the hormone is broadly classified into two types:

Fixed Membrane Receptor Mechanism

This mechanism is characteristic of water-soluble hormones such as amines or proteins, including growth hormone, oxytocin, and antidiuretic hormone. These hormones cannot pass through the lipid membrane and thus bind to receptors located on the cell membrane.

Hormone Binding:

The hormone binds to its specific receptor on the cell membrane.

Activation Of Adenyl Cyclase:

The binding activates the enzyme adenyl cyclase.

Production Of Camp:

The adenyl cyclase converts ATP to cyclic AMP, which acts as the secondary messenger.

Cellular Response:

cAMP freely diffuses in the cell and causes a series of enzymatic reactions finally leading to Biochemical changes

Inactivation Of Camp:

The enzyme phosphodiesterase inactivates the action of cAMP.

Mobile Receptor Mechanism

This mechanism occurs through lipid-soluble hormones like fatty acids and steroids which easily pass through the plasma membrane. The actions of these hormones are through intracellular receptors.

Diffusion In Cell:

The hormones diffuse across the plasma membrane.

Binding To Intracellular Receptor:

The hormones bind to the receptors present in the cytoplasm or nucleus.

Gene Transcription:

The hormone-receptor complex starts the DNA transcription.

Protein Synthesis:

mRNA is translated into proteins, which then produce biochemical changes within the cell.

Hormones As Regulators

The hormones form an important part of the regulation of the body's internal environment. The secretory activity of the hormone can be regulated through the feedback mechanism, which includes :

Positive Feedback Control:

This is a process whereby the end products of an action further enhance the action in a feedback loop. Examples include blood clotting and the menstrual cycle.

Negative Feedback Control:

The final product of an action reduces the stimulus for the same action. Examples include thermoregulation and control of levels of blood sugar.

Hormones As Messengers

The hypothalamic neurosecretory cells release the hormones, also called neurohormones, into the blood. These neurohormones diffuse to the pituitary gland and there trigger the release of several other hormones. For this reason, they are also called "releasing factors."

Signaling Pathways

The signalling pathways are:

Receptor Binding:

The hormone binds to specific receptors on the exterior cell membrane.

Second Messenger Activation:

The binding activated second messengers inside the cell, namely, cAMP, IP3, or DAG.

Cellular Response:

The second messengers trigger a series of actions inside the cell, which ultimately lead to physiological responses.

Steroid and Thyroid Hormones

Steroid and thyroid hormone mechanisms are described as follows:

Cell Diffusion:

The hormone diffuses through the plasma membrane into the cell.

Binding To Intracellular Receptor:

The hormone binds to receptors in the cytoplasm or the nucleus.

Gene Transcription:

The hormone-receptor complex binds to DNA and initiates gene transcription and protein synthesis.

Cellular Response:

The newly synthesized proteins then cause the physiological response.

Examples Of Hormone Action

The examples are mentioned below:

Insulin:

Binds to insulin receptors on the plasma membrane of cells and initiates the signaling transduction which provokes glucose uptake of the cells to decrease blood sugar.

Cortisol:

Diffuses into cells, binds with the intracellular receptor and controls the gene expression that provokes increased production of glucose and anti-inflammatory effects.

Epinephrine:

Binds with the adrenergic receptors of plasma membranes of cells and activates the signal transduction pathway that provokes heartbeats and energy availability.

Regulation of Hormonal Activity

Read about the regulation of hormonal activity:

Feedback Mechanisms:

Feedback mechanisms ensure that the levels of hormones are kept within the homeostatic range. High levels of hormones result in negative feedback that inhibits further release of the hormone.

Receptor Sensitivity:

Receptors may change their sensitivity to the hormone, either intensifying or decreasing the response to a given amount of hormone.

Hormonal Synergism And Antagonism

The effects of hormones are described below:

Synergistic Effects:

Some hormones have effects that enhance each other. The classic example is that of estrogen and progesterone, working together to regulate the menstrual cycle.

Antagonistic Effects:

Some hormones have effects on the body that are opposite or antagonistic to one another. Some classic examples include insulin and glucagon, which respectively lower and raise blood sugar.

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Difference between Endocrine and Exocrine Glands	Difference between Thyroid and Parathyroid
Pancreas Function in the Human Body	Disorders of Pituitary Gland
Adrenal Insufficiency	Hormone Receptors

Frequently Asked Questions (FAQs)

1. What are the two major groups of hormone receptors?

The two major groups are cell surface receptors and intracellular receptors.

2. How do peptide hormones act on target cells?

Peptide hormones bind to cell surface receptors. These, in turn, activate signal transduction or second messenger pathways.

3. What is the function of intracellular receptors in hormone action?

Intracellular receptors bind steroid and thyroid hormones, and through these, regulate gene transcription and protein synthesis.

4. How does insulin act to control blood sugar levels?

Insulin attaches to its receptor, hence the activation of pathways that increase glucose uptake by cells.

5. What are some mechanisms that regulate hormone action?

Some mechanisms that regulate hormone action include feedback mechanisms and receptor sensitivity.

6. What is the role of calcium as a second messenger in hormone action?

Calcium acts as a crucial second messenger in many hormone signaling pathways. When intracellular calcium levels rise (often due to hormone action), it can activate various enzymes, trigger the release of other signaling molecules, or directly affect cellular processes like muscle contraction.

7. How do hormone antagonists work?

Hormone antagonists are molecules that bind to hormone receptors without activating them, thereby blocking the action of the natural hormone. They compete with the hormone for receptor binding sites, effectively reducing or preventing the hormone's biological effects.

8. What is the role of receptor crosstalk in integrating different hormone signals?

Receptor crosstalk occurs when the signaling pathway activated by one hormone influences the signaling of another hormone. This allows for integration of multiple hormonal inputs, enabling more complex and nuanced cellular responses to the overall hormonal environment.

9. What is the concept of hormone cross-talk, and why is it important?

Hormone cross-talk refers to the interaction between different hormone signaling pathways. It's important because it allows for complex regulation of physiological processes, where the effect of one hormone can be modulated by the presence or absence of other hormones, leading to integrated responses.

10. What is the concept of biased signaling in hormone action?

Biased signaling refers to the ability of different ligands (including hormones) to preferentially activate certain signaling pathways over others through the same receptor. This concept explains how different hormones or drugs acting on the same receptor can produce distinct cellular effects.

11. What is the role of receptor oligomerization in hormone action?

Receptor oligomerization, where multiple receptor units come together, can enhance signal transduction, create new binding sites for signaling molecules, or allow for signal integration between different receptor types. This process adds another layer of complexity and regulation to hormone signaling.

12. What is the significance of hormone half-life in understanding hormone action?

Hormone half-life, the time it takes for half of a hormone to be degraded or eliminated, affects the duration of hormone action. Hormones with shorter half-lives allow for more rapid changes in signaling, while those with longer half-lives provide more sustained effects.

13. How do hormone-degrading enzymes contribute to the regulation of hormone action?

Hormone-degrading enzymes play a crucial role in terminating hormone signals by breaking down hormones. This helps to limit the duration of hormone action, prevent overstimulation of target cells, and maintain hormone homeostasis.

14. What is the significance of receptor reserve in hormone action?

Receptor reserve refers to the presence of extra receptors beyond what's needed for a maximal response to a hormone. It's significant because it can allow for a full cellular response even when some receptors are occupied or non-functional, providing a buffer against variations in hormone levels or receptor availability.

15. How do hormones achieve tissue-specific effects despite often having widespread receptor distribution?

Tissue-specific effects of hormones are achieved through several mechanisms: 1) Differential expression of receptor subtypes or isoforms, 2) Presence of tissue-specific co-regulators, 3) Variations in post-receptor signaling components, and 4) Interaction with tissue-specific transcription factors. These factors allow the same hormone to elicit different responses in different tissues.

16. What is a hormone receptor, and why is it important?

A hormone receptor is a specific protein molecule that binds to a particular hormone. It's crucial because it allows cells to recognize and respond to hormones, determining which cells will be affected by a given hormone and what the response will be.

17. How does the concept of "lock and key" apply to hormone-receptor interactions?

The "lock and key" concept describes the specificity of hormone-receptor interactions. Like a key fits only a specific lock, a hormone (the key) can only bind to its corresponding receptor (the lock). This ensures that hormones trigger responses only in cells with the appropriate receptors.

18. How do steroid hormones exert their effects on target cells?

Steroid hormones, being lipid-soluble, enter cells and bind to intracellular receptors. This hormone-receptor complex then moves to the nucleus, where it binds to specific DNA sequences and regulates gene transcription, leading to changes in protein synthesis and cellular function.

19. How do peptide hormones typically initiate their effects?

Peptide hormones bind to cell surface receptors, often triggering the activation of enzymes like adenylyl cyclase or phospholipase C. This leads to the production of second messengers such as cAMP or IP3, which then propagate the signal within the cell.

20. What is a hormone-response element (HRE)?

A hormone-response element is a specific DNA sequence that a hormone-receptor complex binds to in order to regulate gene expression. HREs are crucial for the genomic effects of hormones, particularly steroid and thyroid hormones.

21. What is the difference between autocrine, paracrine, and endocrine signaling in hormone action?

Autocrine signaling involves a cell secreting a hormone that acts on itself. Paracrine signaling occurs when a hormone acts on nearby cells. Endocrine signaling, the most common for hormones, involves hormones being released into the bloodstream and acting on distant target cells.

22. How do scaffold proteins contribute to hormone signaling?

Scaffold proteins are molecules that bring together multiple components of a signaling pathway. They enhance the efficiency and specificity of hormone signaling by organizing signaling molecules into complexes, facilitating their interactions and localizing the response to specific cellular regions.

23. What is the mechanism of hormone action?

The mechanism of hormone action refers to how hormones interact with target cells to produce specific biological responses. It typically involves hormones binding to receptors, which then trigger intracellular signaling cascades that lead to changes in cell function or gene expression.

24. How do lipid-soluble hormones differ from water-soluble hormones in their mechanism of action?

Lipid-soluble hormones can pass through the cell membrane and bind to intracellular receptors, while water-soluble hormones bind to receptors on the cell surface. This difference affects how quickly they can initiate a response and the type of signaling pathways they activate.

25. What is the difference between genomic and non-genomic effects of hormones?

Genomic effects involve hormones altering gene expression, typically taking hours to days to manifest. Non-genomic effects are rapid responses that don't involve changes in gene expression, often occurring within seconds to minutes through direct protein modifications.

26. How do nuclear receptors differ from membrane-bound receptors?

Nuclear receptors are located inside the cell and typically bind to lipid-soluble hormones. They directly interact with DNA to regulate gene expression. Membrane-bound receptors, on the other hand, are on the cell surface and usually bind water-soluble hormones, initiating signaling cascades without directly interacting with DNA.

27. What is the role of phosphorylation in hormone signaling?

Phosphorylation, the addition of a phosphate group to a molecule, is a key mechanism in hormone signaling. It can activate or inactivate enzymes, alter protein conformations, and create binding sites for other molecules, thereby propagating and modulating the hormone signal.

28. How do hormone-binding proteins in the blood affect hormone action?

Hormone-binding proteins in the blood, such as sex hormone-binding globulin, can regulate hormone availability and action. They can prolong hormone half-life by protecting them from degradation, but also limit the amount of free hormone available to interact with receptors, thus modulating hormone effects.

29. How do allosteric modulators affect hormone action?

Allosteric modulators are substances that bind to a receptor at a site different from the hormone binding site. They can enhance (positive modulators) or reduce (negative modulators) the effect of the hormone by changing the receptor's conformation or affinity for the hormone.

30. What is the concept of biased agonism in hormone action?

Biased agonism refers to the ability of a hormone or drug to preferentially activate one signaling pathway over another through the same receptor. This concept is important because it explains how different ligands for the same receptor can produce distinct cellular responses.

31. How do hormone mimics or endocrine disruptors interfere with normal hormone action?

Hormone mimics or endocrine disruptors are substances that can bind to hormone receptors or interfere with hormone synthesis, transport, or metabolism. They can disrupt normal endocrine function by inappropriately activating or blocking hormone signaling pathways.

32. What is the concept of hormone sensitivity, and how can it change?

Hormone sensitivity refers to how responsive a cell or tissue is to a hormone. It can change through alterations in receptor number, affinity, or post-receptor signaling components. Factors like prolonged hormone exposure or certain physiological states can increase or decrease hormone sensitivity.

33. What is the role of receptor desensitization in hormone action?

Receptor desensitization is a process where cells become less responsive to a hormone after prolonged or repeated exposure. This can occur through receptor internalization, degradation, or modification, and serves as a regulatory mechanism to prevent overstimulation by hormones.

34. How do epigenetic modifications influence hormone action?

Epigenetic modifications, such as DNA methylation or histone modifications, can alter how genes respond to hormones. These changes can affect the accessibility of hormone-response elements or the expression of hormone receptors, thereby modulating cellular sensitivity to hormones without changing the DNA sequence.

35. How do hormones regulate their own receptors?

Hormones can regulate their own receptors through processes like up-regulation (increasing receptor number or sensitivity) or down-regulation (decreasing receptor number or sensitivity). This self-regulation helps maintain appropriate cellular responsiveness to hormones over time.

36. What is the significance of hormone pulsatility?

Hormone pulsatility refers to the rhythmic release of hormones in pulses or bursts. This pulsatile pattern is important for maintaining receptor sensitivity, regulating gene expression, and coordinating complex physiological processes like the menstrual cycle or growth hormone release.

37. How do hormones achieve cell-specific responses despite circulating throughout the body?

Cell-specific responses are achieved through the presence of specific receptors on target cells. Only cells with the appropriate receptors will respond to a particular hormone, even though the hormone circulates throughout the body in the bloodstream.

38. How do membrane-bound receptors transmit signals across the cell membrane?

Membrane-bound receptors transmit signals by changing their conformation when a hormone binds. This conformational change can activate intracellular enzymes, open ion channels, or interact with G proteins, initiating intracellular signaling cascades.

39. What is the role of receptor tyrosine kinases in hormone signaling?

Receptor tyrosine kinases are a type of cell surface receptor that, when activated by hormone binding, phosphorylate specific tyrosine residues on target proteins. This initiates signaling cascades that can lead to changes in cell growth, differentiation, and metabolism.

40. How does negative feedback regulate hormone action?

Negative feedback is a regulatory mechanism where the end product of a hormone's action inhibits further hormone production or release. This helps maintain homeostasis by preventing excessive hormone activity and keeping hormone levels within a normal range.

41. What is the role of receptor internalization in hormone signaling?

Receptor internalization is a process where hormone-bound receptors are taken into the cell. This can serve to terminate the hormone signal, recycle receptors back to the cell surface, or in some cases, continue signaling from within intracellular compartments.

42. How do co-activators and co-repressors modulate hormone action at the genomic level?

Co-activators and co-repressors are proteins that interact with hormone-receptor complexes bound to DNA. Co-activators enhance gene transcription, while co-repressors suppress it. They provide an additional layer of regulation in hormone-mediated gene expression.

43. How do changes in membrane fluidity affect hormone receptor function?

Membrane fluidity can affect how easily receptors move within the membrane and how they interact with other membrane components. Changes in fluidity can therefore impact receptor clustering, internalization, and interaction with signaling molecules, potentially altering hormone responsiveness.

44. What is the significance of hormone receptor dimerization?

Receptor dimerization, where two receptor molecules come together, is often a crucial step in hormone signaling. It can increase the specificity and strength of hormone binding, activate the receptor's enzymatic activity, or create new binding sites for other signaling molecules.

45. What is signal transduction in hormone action?

Signal transduction is the process by which a hormone's message is converted into intracellular changes. It involves a series of biochemical reactions that amplify the initial hormone-receptor interaction, leading to the final cellular response.

46. How does the concept of signal amplification apply to hormone action?

Signal amplification in hormone action refers to the process where a small number of hormone molecules can produce a large cellular response. This occurs through cascading reactions in signaling pathways, where each step activates multiple molecules of the next component.

47. How do second messengers contribute to hormone action?

Second messengers are molecules inside the cell that relay and amplify the signal from a hormone-receptor complex. They allow a single hormone molecule to trigger a large intracellular response, increasing the efficiency and speed of hormone action.

48. What is the role of G proteins in hormone signaling?

G proteins are intermediary molecules that connect hormone receptors to effector proteins. When a hormone binds to its receptor, it activates the G protein, which then interacts with other proteins to produce cellular responses, playing a crucial role in signal amplification.

49. What is the role of protein kinases in hormone action?

Protein kinases are enzymes that phosphorylate other proteins, often activated as part of hormone signaling cascades. They play a crucial role in signal transduction by modifying the activity of various cellular proteins, leading to changes in cell function.

50. How do nuclear localization signals contribute to the action of steroid hormones?

Nuclear localization signals are specific amino acid sequences that direct proteins to the cell nucleus. In steroid hormone signaling, these signals on hormone-receptor complexes ensure that the complex enters the nucleus where it can interact with DNA and regulate gene expression.

51. What is the significance of hormone receptor polymorphisms?

Hormone receptor polymorphisms are genetic variations in receptor genes that can affect hormone binding or signaling. They are significant because they can lead to individual differences in hormone responsiveness, potentially influencing disease susceptibility or treatment outcomes.

52. What is the concept of non-classical hormone signaling?

Non-classical hormone signaling refers to hormone effects that occur through pathways different from the traditionally described mechanisms. This can include rapid, non-genomic effects of steroid hormones or novel signaling pathways for peptide hormones, expanding our understanding of hormone action.

53. How do post-translational modifications of hormone receptors affect signaling?

Post-translational modifications like phosphorylation, ubiquitination, or glycosylation can alter receptor function, localization, or stability. These modifications provide a mechanism for fine-tuning receptor activity and can influence the strength, duration, or specificity of hormone signaling.

54. How do lipid rafts in cell membranes affect hormone signaling?

Lipid rafts are specialized membrane domains that can concentrate certain receptors and signaling molecules. They play a role in hormone signaling by facilitating the interaction between receptors and their downstream effectors, potentially enhancing the efficiency and specificity of signal transduction.

55. How do scaffold proteins contribute to the specificity of hormone signaling?

Scaffold proteins enhance signaling specificity by organizing signaling components into discrete complexes. This spatial organization can prevent crosstalk between different pathways, ensure that signals are transmitted to the correct downstream effectors, and allow for pathway-specific responses to hormones.