Hormonieritys

Hormonieritys is the process by which cells release hormones into the extracellular space, enabling chemical signals to coordinate physiological functions. Hormones may act at distant sites via the bloodstream (endocrine secretion), be released into local tissue spaces to affect neighboring cells (paracrine), or act on the secreting cell itself (autocrine). Neurosecretory cells provide a bridge between the nervous system and the endocrine system.

Secretory mechanisms vary: many peptide and protein hormones are stored in secretory granules and released by exocytosis in response to stimuli, whereas steroid and thyroid hormones may be synthesized on demand and diffuse into circulation. Secretion can be constitutive, continuous at a low rate, or regulated, triggered by neural input, hormonal signals, or changes in ion or nutrient concentrations. Secretions often occur in pulses and follow circadian or ultradian rhythms, improving signal specificity and receptor sensitivity.

Transport and action: once in the bloodstream, hormones may bind carrier proteins or circulate freely. Target cells respond when a hormone binds specific receptors, initiating signal transduction pathways that alter gene expression, metabolism, growth, or reproduction. The effects and duration depend on receptor type, second messengers, and hormone clearance, which mainly occurs in the liver and kidneys.

Regulation and clinical relevance: Hormonieritys is tightly controlled by feedback systems, notably the hypothalamic-pituitary axis. Dysregulation can underlie endocrine disorders such as diabetes mellitus (insufficient insulin secretion), hyperthyroidism, or Cushing's syndrome. Diagnoses rely on measuring hormone levels and stimulation tests, while therapies include hormone replacement and receptor-targeted drugs.