hormoneschemical

Hormones are chemical messengers that regulate physiology by coordinating activity across tissues. They are produced by glands and specialized cells and released into the bloodstream or surrounding fluids to reach target cells that express specific receptors.

Chemically, hormones fall into several broad classes: peptide and protein hormones (such as insulin and growth hormone); steroid hormones derived from cholesterol (such as cortisol and estrogen); and amino acid derivatives (such as epinephrine and thyroid hormones). Lipid-soluble hormones, including steroids and thyroid hormones, tend to act on intracellular receptors and influence gene transcription, while water-soluble hormones, such as peptides and most amines, bind to cell-surface receptors and initiate rapid signaling cascades.

Mechanisms of action involve binding to specific receptors, which activates intracellular signaling pathways (for example, cAMP or IP3/DAG cascades) or alters gene expression. Hormone effects can be rapid or gradual and may last from minutes to days. Receptors may be located on the cell surface or inside the cell, depending on the chemical nature of the hormone.

Regulation and health considerations: Hormone levels are tightly controlled by feedback mechanisms, often involving neural signals and other hormones. Dysregulation can lead to disorders such as hypo- or hyperthyroidism, diabetes, adrenal abnormalities, and reproductive issues. Hormones interact with multiple signaling systems, coordinating metabolism, growth, reproduction, stress responses, and other essential functions.

In plants, phytohormones perform analogous regulatory roles, including auxins, cytokinins, gibberellins, abscisic acid, and ethylene, guiding growth, development, and responses to environmental conditions.