Lipid-based hormones are a class of signaling molecules derived primarily from cholesterol, characterized by their lipophilic, or fat-soluble, chemical structure. The major groups include steroid hormones, such as androgens, estrogens, progestins, glucocorticoids, and mineralocorticoids, as well as thyroid hormones. Their fat-soluble nature allows them to readily diffuse across the cell membrane, enabling them to exert their profound effects by interacting with intracellular receptors and directly modulating gene expression.
Origin
The concept of lipid-based hormones is fundamental to endocrinology, dating back to the isolation and structural determination of steroid molecules in the early 20th century. The term emphasizes their biochemical origin from lipids, specifically cholesterol, and their distinct mechanism of action compared to water-soluble peptide hormones. This classification is crucial for understanding their transport in the blood, their half-life, and their therapeutic delivery methods.
Mechanism
The mechanism of action is primarily genomic, meaning they directly influence the cell’s DNA transcription. Once secreted, these hormones bind to transport proteins in the blood, and upon reaching the target cell, they diffuse across the plasma membrane. Inside the cell, they bind to specific intracellular receptors, forming a hormone-receptor complex that translocates to the nucleus. This complex then binds to hormone response elements (HREs) on the DNA, either activating or repressing the transcription of specific genes, leading to the synthesis of new proteins that mediate the hormone’s long-term physiological effects.
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