The Endocrine System. The Classification of Hormones
A hormone is classically defines as a chemical that is secreted into the blood and acts on a distant target in very low concentrations. Hormones can be classified according to source or location - heart, liver, pineal gland, hypothalamus, pituitary, thyroid, parathyroid, thymus, pancreas, adrenal cortex, adrenal medulla, kidney, skin, testis, ovaries, adipose tissue, and placenta. Hormones can be divided into 3 main chemical classes: Peptide and protein hormones composed of linked amino acids Steroid hormones are derived from cholesterol The amine hormones are derivatives of tryptophan or tyrosine Most hormones are Peptides or Proteins If a hormone is not a steroid or a amine it is probably a peptide. A steroid-producing cell would have extensive smooth Endoplasmic Reticulum; a protein-producing cell would have lots of Rough Endoplasmic Reticulum. Usually made in tissues all over the body unlike steroids that are made only in a few organs Peptide Hormone S...