hormooneja

Hormones are chemical messengers produced by glands and specialized cells in animals. They are released into body fluids and travel to distant target tissues where they elicit specific physiological responses. Hormones operate at very low concentrations and regulate processes such as growth, metabolism, reproduction, water and electrolyte balance, and responses to stress.

Hormones can be classified by chemical structure into peptide or protein hormones (such as insulin and growth hormone), steroid hormones (such as cortisol, estrogen, and testosterone), and amine hormones (such as adrenaline and thyroid hormones). They originate in organs including the pituitary, hypothalamus, thyroid, parathyroid, adrenal glands, pancreas, and gonads, but many tissues such as the gut, liver, adipose tissue, and placenta also produce hormones.

Mechanism of action: water-soluble hormones bind to cell-surface receptors and trigger signaling cascades; lipid-soluble hormones pass through membranes and interact with intracellular receptors to regulate gene expression. The effects may be rapid or delayed, influencing metabolism, growth, and function over different time scales.

Regulation: hormone levels are controlled by feedback mechanisms, often via the hypothalamic-pituitary axis. Circadian rhythms, stress, and nutritional status influence secretion. Hormones can interact in synergistic, permissive, or antagonistic ways to shape physiological outcomes.

Clinical relevance: abnormal hormone production causes endocrine disorders such as hypothyroidism and diabetes mellitus. Treatments include hormone replacement, receptor antagonists, and lifestyle changes. Diagnostic assessment uses measurements of hormone levels in blood, urine, or saliva to support diagnosis and monitoring.

History and overview: The term hormone was coined in the early 20th century to describe chemical messengers from glands. Today, endocrinology studies hormones' synthesis, receptors, signaling pathways, and their roles in health and disease.