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A hormone is a secreted chemical messenger that enables communication between cells and tissues throughout the body. Learning Objectives
Key Points
Key Terms
A hormone is a chemical messenger that enables communication between cells. Hormones are secreted by the glands of the endocrine system and they serve to maintain homeostasis and to regulate numerous other systems and processes, including reproduction and development. Hormone SignalingThe glands of the endocrine system secrete hormones directly into the extracellular environment. The hormones then diffuse to the bloodstream via capillaries and are transported to the target cells through the circulatory system. This allows hormones to affect tissues and organs far from the site of production or to apply systemic effects to the whole body. Hormone-producing cells are typically specialized and reside within a particular endocrine gland, such as thryocytes in the thyroid gland. Hormones exit their cell of origin through the process of exocytosis or by other means of membrane transport. Cellular recipients of a particular hormonal signal may be one of several cell types that reside within a number of different tissues. This is so in the case of insulin, which triggers a diverse range of systemic physiological effects. Different tissue types may also respond differently to the same hormonal signal. As a result, hormonal signaling is elaborate and hard to dissect. Hormones activate target cells by diffusing through the plasma membrane of the target cells (lipid-soluble hormones) to bind a receptor protein within the cytoplasm of the cell, or by binding a specific receptor protein in the cell membrane of the target cell (water-soluble proteins). In both cases, the hormone complex will activate a chain of molecular events within the cell that will result in the activation of gene expression in the nucleus. The reaction of the target cells may then be recognized by the original hormone-producing cells, leading to a down-regulation in hormone production. This is an example of a homeostatic negative feedback loop. Lipid-soluble hormone receptor activation: Nuclear hormone receptors are activated by a lipid-soluble hormone such as estrogen, binding to them inside the cell. Lipid-soluble hormones can cross the plasma membrane. Steps of Hormonal Signaling
Water-soluble hormone receptor activation: Water-soluble hormones, such as epinephrine, bind to a cell-surface localized receptor, initiating a signaling cascade using intracellular second messengers. Hormone ClassesHormones are typically divided into three classes:
15.2A: Mechanisms of Hormone Action is shared under a CC BY-SA license and was authored, remixed, and/or curated by LibreTexts. What are the methods of hormone action?There are two modes of hormonal action. A: Activation of cell-surface receptors and coupled second-messenger systems, with a variety of intracellular consequences. B: Entry of hormone into the target cell, binding to and activation of an intracellular (more...)
What are the 4 classes of hormones?Summary. libid-derived hormones.. amino acid-derived hormones.. peptide hormones.. glycoprotien hormones.. What are the 3 different types classes of hormones?There are three major types of hormones.. Protein hormones (or polypeptide hormones) are made of chains of amino acids. An example is ADH (antidiuretic hormone) which decreases blood pressure.. Steroid hormones are derived from lipids. ... . Amine hormones are derived from amino acids.. What is the mode of action of hormones quizlet?What is the mode of action of hormones? - Peptide hormones bind to cell-surface receptors and result in the activation of enzymes. - Steroid hormones enter the cell, usually bind to receptors in the nucleus and result in the activation of certain genes.
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