Hormones are chemical messengers. Ch. 30 Animal Hormones Hormones are chemical messengers.

Endocrine System Endocrine and Exocrine Secretions Endocrine cells secrete endocrine signals Endocrine glands are secretory organs Hormones are endocrine signals that are released into the bloodstream Paracrine, autocrine and hormones have target cells that respond to their signals Paracrine signals act on nearby cells, autocrine signals stimulate the same cell that produces them. Target cells have receptor proteins that recognize and bind to a signal.

Hormones: 3 groups Peptide and protein Steroid Amine Large molecules and water soluble Packaged in vesicles and released by exocytosis Steroid Made from cholesterol and have 4 rings Lipid soluble but do not dissolve well in blood plasma Amine Small molecules from single amino acids Can be water soluble or lipid-soluble Peptide hormones must have receptors on the outside of target cell. Steroid hormones (lipid-soluble) have receptors on the inside of target cells. Amine hormones such as thyroxine and epinephrine are made from tyrosine. Depending on whether the modified amino acid is polar or non polar an amine hormone can be water or lipid soluble.