Hormónum

Hormónum are chemical messengers produced by specialized cells in glands and other tissues that are released into the bloodstream to regulate the activity of distant target cells. In Icelandic-language texts, hormónum refers to these substances. They influence metabolism, growth, development, reproduction, and the body’s response to stress and environmental changes.

Most hormones fall into three broad chemical classes: peptide and protein hormones (such as insulin and growth hormone); steroid hormones (including cortisol, testosterone, and estrogen); and amine hormones derived from amino acids (such as adrenaline and thyroid hormones). They are produced in various organs, notably the hypothalamus and pituitary, thyroid and parathyroid glands, adrenal glands, pancreas, gonads, and in other tissues such as the gut and adipose tissue.

Hormones act by binding to receptors that initiate cellular signaling. Peptide hormones bind to surface receptors and commonly activate second messenger systems like cAMP or IP3/DAG. Steroid and thyroid hormones, being lipophilic, cross the cell membrane and bind intracellular receptors that influence gene transcription. Hormones are transported in the blood; peptides typically circulate freely or bound weakly, while steroids and thyroid hormones are largely bound to carrier proteins, which extends their half-life.

Regulation of hormone secretion is usually controlled by feedback loops, especially involving the hypothalamus and pituitary, to maintain homeostasis. Disruptions can lead to endocrine disorders such as diabetes, thyroid diseases, or adrenal disorders. Therapeutic approaches include hormone replacement, receptor agonists or antagonists, and targeted modulation of hormone synthesis or action.