D5  Hormones and Metabolism

big ninja

Essential Idea:

Hormones are not secreted at a uniform rate

and exert their effect at low concentrations


  • Endocrine glands secrete hormones directly into the bloodstream
  • Steroid hormones bind to receptor proteins in the cytoplasm of the target cell to form a receptor-hormone complex
  • The receptor-hormone complex promotes the transcription of specific genes
  • Peptide hormones bind to receptors in the plasma membrane of the target cell
  • Binding of hormones to membrane receptors activates a cascade mediated by a second messenger inside the cell
  • The hypothalamus controls hormone secretion by the anterior and posterior lobes of the pituitary gland
  • Hormones secreted by the pituitary control growth, developmental changes, reproduction and homeostasis


  • Some athletes take growth hormones to build muscles
  • Control of milk secretion by oxytocin and prolactin