Veterinary Physiology-III

CHEMICAL CLASSIFICATION OF HORMONES

• Chemical structure determines
  • solubility and transport characteristics
  • degradation rate (plasma half-life)
  • storage
  • route of exogenous administration

Hormones	Characteristics
Peptides	Structure : chains of amino acids; contain amino terminal (N-terminal) and carboxy terminal (C-terminal) ends; linear - ring or two chains - carbohydrate residues (= glycoproteins). Solubility: hydrophilic Synthesis: rough ER, packaged in Golgi complex Storage: secretory granules Secretion: exocytosis Transport: mostly as a free hormone Receptor site: surface of target cell Action: channel changes or second messenger system
Amines	Catecholamines (dopamine, epinephrine, and norepinephrine) Structure: tyrosine derivative Solubility: hydrophilic Synthesis: cytosol Storage: secretory (chromaffin) granules Secretion: exocytosis Transport: as a free hormone and bound to plasma proteins Receptor site: surface of target cell Action: second messenger system Thyroid hormones Structure: iodinated tyrosine derivative Solubility: lipophilic Synthesis: extracellular colloid Storage: extracellular colloid Secretion: endocytosis of colloid Transport: mostly bound to plasma proteins Receptor site: inside of target cell Action: direct effects on genes ® production of new proteins
Steroids	Mineralocorticoids, glucocorticoids, sex hormones, and vitamin D Structure: cholesterol derivatives, lipids, steroid ring (3 six-membered and 1 five-membered ring) Solubility: lipophilic Synthesis: stepwise modification of cholesterol molecule in various intracellular compartments (in the endocrine gland and also in the blood and target tissues) Storage: hormones not stored, only precursor (cholesterol) stored. Secretion: diffusion Transport: mostly bound to plasma proteins Receptor site: inside of target cell Action: direct effects on genes for production of new proteins
Fatty acid derivatives	Structure: Fatty acid Solubility: Lipoophilic