Hormonal signaling across this hierarchy involves the following:
- Biosynthesis of a particular hormone in a particular tissue
- Storage and secretion of the hormone
- Transport of the hormone to the target cell(s)
- Recognition of the hormone by an associated cell membrane or intracellular receptor protein.
- Relay and amplification of the received hormonal signal via a signal transduction process: This then leads to a cellular response. 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.
- Degradation of the hormone.
As can be inferred from the hierarchical diagram, hormone biosynthetic cells are typically of a specialized cell type, residing within a particular endocrine gland, such as thyroid gland, ovaries, and testes.
Hormones exit their cell of origin via exocytosis or another means of membrane transport. The hierarchical model is an oversimplification of the hormonal signaling process.
Cellular recipients of a particular hormonal signal may be one of several cell types that reside within a number of different tissues, as is the case for insulin, which triggers a diverse range of systemic physiological affects. Different tissue types may also respond differently to the same hormonal signal. Because of this, hormonal signaling is elaborate and hard to dissect.
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