Hormones
Peptide Hormones | Steroid Hormones | Catecholamines | Thyroid Hormones | |
Synthesis and Storage | Made in advance: stored n secretory vesicles | Synthesized on demand from precursors | Made in advance; stored in secretory vesicles | Made in advance; precursor stored in secretory vesicles |
Release from Parent Cell | Exocytosis | Simple diffusion | Exocytosis | Transport protein |
Transport in Blood | Dissolved in plasma | Bound to carrer proteins | Dissolved in plasma | Bound to carrier proteins |
Half-Life | Short | Long | Short | Long |
Location of Receptor | Cell membrane | Cytoplasm or nucleus; some have membrane receptors also | Cell membrane | Nucleus |
Response to Recep-tor-Ligand Binding | Activation of second messenger systems; may activate genes | Activation of genes for transcription and transla-tion; may have nonge-nomic actions | Activation of second messenger systems | Activation of genes for transcription and translation |
General Target Response | Modification of existing proteins and induction of new protein synthesis | Induction of new protein synthesis | Modification of existing proteins | Induction of new protein synthesis |
Examples | Insulin, parathyroid hormone | Estrogen, androgens. cortisol | Epinephrine, norepi-nephrine, dopamine | Thyroxine (Ta) |