THINGS NOBODY TOLD YOU ABOUT MECHANISM OF HORMONE ACTIONS
Mechanism of action of peptide hormones
Peptide hormones are a class of hormones that consist of short chains of amino acids. They are produced and released by various glands and tissues in the body, including the hypothalamus, pituitary gland, pancreas, and adrenal glands. These hormones play crucial roles in regulating various physiological processes in the body.
The mechanism of action of peptide hormones involves several steps:
- Synthesis and release: Peptide hormones are synthesized as larger precursor molecules within specific cells or glands. These precursors undergo post-translational modifications, including cleavage and folding, to form the active hormone. Once synthesized, the hormone is stored in secretory vesicles within the cell. When a signal is received, such as a neural or hormonal stimulus, the vesicles fuse with the cell membrane, allowing the release of the hormone into the bloodstream.
- Circulation and target cell recognition: Once released into the bloodstream, peptide hormones circulate throughout the body. They bind to specific receptors on the surface of target cells, which are cells equipped with receptors capable of recognizing and interacting with the specific peptide hormone. These receptors are often G protein-coupled receptors or receptor tyrosine kinases, depending on the specific hormone.
- Receptor activation: When a peptide hormone binds to its specific receptor on the surface of the target cell, it triggers a series of events that leads to receptor activation. This activation can occur through various mechanisms, including conformational changes in the receptor or the recruitment of intracellular signaling molecules.
- Intracellular signaling: Once the receptor is activated, it initiates a cascade of intracellular signaling events. These events involve the activation of various intracellular proteins and signaling pathways, such as cyclic adenosine monophosphate (cAMP) pathway, phosphoinositide pathway, or mitogen-activated protein kinase (MAPK) pathway. These pathways mediate the transmission of the hormone signal from the cell surface to the nucleus or other intracellular compartments.
- Cellular response: The intracellular signaling pathways triggered by the peptide hormone ultimately lead to specific cellular responses. These responses can include changes in gene expression, enzyme activity, ion channel opening or closing, or alterations in cellular metabolism. The nature of the response depends on the specific peptide hormone and the target cell type.
- Feedback regulation: Once the desired effect is achieved, the peptide hormone signaling is often subject to feedback regulation to maintain homeostasis. Feedback mechanisms can involve the inhibition or stimulation of hormone synthesis and release, alterations in receptor expression or sensitivity, or the activation of antagonistic signaling pathways.
Overall, the mechanism of action of peptide hormones involves their synthesis, release, circulation, recognition by specific receptors on target cells, receptor activation, intracellular signaling, cellular response, and feedback regulation. By modulating these processes, peptide hormones play critical roles in regulating a wide range of physiological functions in the body.
Amino Acid Derivatives Mechanism
Amino acid derivatives are a class of hormones that are derived from amino acids, the building blocks of proteins. These hormones play important roles in various physiological processes within the body. The mechanism of action of amino acid derivatives hormones can vary depending on the specific hormone in question. However, I will describe the general mechanisms for two well-known amino acid derivatives hormones: epinephrine (adrenaline) and thyroxine.
- Epinephrine (Adrenaline): Epinephrine is produced by the adrenal glands and plays a crucial role in the “fight-or-flight” response. The mechanism of action of epinephrine involves binding to specific cell surface receptors called adrenergic receptors. These receptors are classified into two main types: alpha and beta adrenergic receptors. Upon binding to the receptor, epinephrine triggers a cascade of intracellular events through a G protein-mediated pathway.
For example, when epinephrine binds to beta-adrenergic receptors on target cells, it activates a G protein associated with the receptor. This activation leads to the production of a second messenger molecule called cyclic adenosine monophosphate (cAMP) within the cell. cAMP then activates protein kinase A (PKA), which subsequently phosphorylates various intracellular proteins.
The phosphorylation of these proteins by PKA leads to a wide range of physiological effects, including increased heart rate, elevated blood pressure, dilation of airways, and increased breakdown of glycogen into glucose in the liver. These responses help prepare the body for immediate action in response to a perceived threat.
- Thyroxine (T4): Thyroxine, also known as T4, is produced by the thyroid gland and plays a vital role in regulating metabolism and growth. The mechanism of action of thyroxine involves its binding to nuclear receptors called thyroid hormone receptors (THR) located within the target cells.
Thyroxine is synthesized and released into the bloodstream as an inactive form, and most of it is converted to its active form, triiodothyronine (T3), within the target cells. Once inside the cells, T3 binds to THR, forming a hormone-receptor complex that can directly bind to specific DNA sequences called thyroid response elements (TREs) within the genes.
The binding of T3-THR complex to TREs modulates gene expression, either by promoting or inhibiting the transcription of specific genes. This leads to changes in the synthesis of various proteins, which affects metabolism, growth, and development throughout the body.
In summary, amino acid derivatives hormones, such as epinephrine and thyroxine, exert their effects by binding to specific receptors on target cells. The subsequent activation of intracellular signaling pathways or modulation of gene expression results in various physiological responses and adaptations within the body.
Cholesterol Hormone Mechanism
Cholesterol derivatives, also known as cholesterol-based hormones or steroidal hormones, are a class of hormones that are derived from cholesterol and play essential roles in various physiological processes. The mechanism of action of these hormones involves their ability to bind to specific receptors located in target cells, initiating a cascade of events that ultimately lead to specific cellular responses.
Here is a general overview of the mechanism of action of cholesterol derivatives hormones:
- Hormone synthesis: Cholesterol derivatives hormones, such as cortisol, estrogen, progesterone, and testosterone, are synthesized in specialized endocrine glands or tissues. These hormones are produced through a series of enzymatic reactions that modify the cholesterol molecule, resulting in the formation of specific hormones with distinct chemical structures.
- Hormone release: Once synthesized, cholesterol derivatives hormones are released into the bloodstream and transported to target tissues or organs. Hormone release is often regulated by feedback mechanisms involving other hormones or physiological signals.
- Binding to receptors: Upon reaching the target cells, cholesterol derivatives hormones interact with specific receptors located either on the cell surface (membrane receptors) or inside the cell (intracellular receptors). The receptors are typically proteins that are specific to a particular hormone and are expressed in specific tissues or cell types.
- Receptor activation: When a hormone binds to its receptor, it induces conformational changes in the receptor protein, leading to the activation of the receptor. This activation can occur through various mechanisms, depending on whether the receptor is a membrane receptor or an intracellular receptor.
- Intracellular signaling (membrane receptors): If the hormone receptor is located on the cell membrane, hormone binding triggers intracellular signaling pathways. This often involves the activation of second messenger molecules, such as cyclic adenosine monophosphate (cAMP), inositol trisphosphate (IP3), or calcium ions, which transmit the hormone signal from the cell surface to the intracellular compartments.
- Nuclear translocation (intracellular receptors): If the hormone receptor is located inside the cell, such as in the cytoplasm or nucleus, hormone binding results in the formation of a hormone-receptor complex. This complex then translocates into the nucleus, where it binds to specific DNA sequences called hormone response elements (HREs) within target genes.
- Gene regulation: Once bound to HREs, the hormone-receptor complex acts as a transcription factor, modulating the expression of target genes. This can lead to the upregulation or downregulation of specific genes, ultimately altering the production of proteins and influencing various cellular processes.
- Cellular response: The altered gene expression triggered by the hormone-receptor complex results in specific cellular responses. These responses can include changes in protein synthesis, enzymatic activity, cell growth, differentiation, or other physiological processes, depending on the specific hormone and target tissue.
Overall, the mechanism of action of cholesterol derivatives hormones involves their binding to specific receptors, initiating a signaling cascade that culminates in the regulation of gene expression and subsequent cellular responses. This intricate process allows these hormones to exert their wide-ranging effects on various tissues and organs throughout the body.
Eicosanoid Mechanism Summary
Fatty acid hormone derivatives, also known as eicosanoids, are signaling molecules derived from arachidonic acid, a polyunsaturated fatty acid found in cell membranes. These compounds play crucial roles in various physiological processes, including inflammation, pain modulation, blood pressure regulation, and blood clotting. There are three major types of eicosanoids: prostaglandins, thromboxanes, and leukotrienes.
The synthesis of eicosanoids begins with the release of arachidonic acid from cell membrane phospholipids, which is catalyzed by the enzyme phospholipase A2. Once released, arachidonic acid can be metabolized by different enzymes to form different types of eicosanoids.
Prostaglandins are synthesized through the action of the enzyme cyclooxygenase (COX). There are two isoforms of COX: COX-1 and COX-2. COX-1 is constitutively expressed and involved in maintaining physiological processes, such as protecting the stomach lining and regulating blood platelets. COX-2, on the other hand, is induced during inflammation and plays a key role in the production of prostaglandins involved in pain, fever, and inflammation. COX enzymes convert arachidonic acid into prostaglandin H2 (PGH2), which is then further metabolized by specific synthases into various types of prostaglandins. Prostaglandins exert their effects by binding to specific G-protein coupled receptors on the cell surface, initiating intracellular signaling pathways and modulating cellular responses.
Thromboxanes are also derived from arachidonic acid through the action of COX enzymes. In platelets, COX-1 converts arachidonic acid into thromboxane A2 (TXA2), which promotes platelet aggregation and vasoconstriction. Thromboxanes play a critical role in the formation of blood clots and regulation of blood flow.
Leukotrienes, on the other hand, are synthesized through the action of lipoxygenase enzymes. Arachidonic acid is converted by lipoxygenases into leukotriene A4 (LTA4), which can further undergo specific modifications to produce various leukotrienes, such as leukotriene B4 (LTB4) and cysteinyl leukotrienes (LTC4, LTD4, and LTE4). Leukotrienes are involved in mediating allergic and inflammatory responses, particularly in the respiratory system. They can bind to specific receptors on target cells, leading to bronchoconstriction, increased mucus production, and recruitment of inflammatory cells.
Overall, the mechanism of action of fatty acid hormone derivatives involves their synthesis from arachidonic acid by specific enzymes and subsequent binding to specific receptors on target cells. Through these interactions, eicosanoids modulate various physiological processes and contribute to the regulation of inflammatory and immune responses in the body.
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