1.  
   • Hormones are released from neural, non neuronal or endocrine cells
   • Endocrine cells can be organized into a gland (endocrine glands)
   • Hormones affect distant targets
   • Responses are slow and may last days
   • Is effective at low concentrations (10-12M)

• Autocrine: A locally acting chemical signal that binds to receptors and exerts a regulatory effect on the same cell that secreted it.
• Paracrine: A locally acting chemical signal that binds to receptors and exerts a regulatory effect on cells in the neighborhood of the cell that released it.
• Intracrines are signaling molecules that tend to be hormones or peptide growth factors that function within cells.  They are either synthesized by the cell or internalized from extracellular space.

Chemical classes of hormones and their synthesis, storage and release

1. Steroid hormones
2. Peptides
3. Amine hormones

• Cholesterol
• can be obtained from diet
• Synthesized in the liver and endocrine cells
• Low density lipoproteins carry cholesterol to cells that use cholesterol
• Uptake is through endocytosis
• High density lipoproteins carry cholesterol away from cells to the liver.
• Steroids are synthesized in the gonads and adrenal cortex and are NOT stored