Chapter 1: Overview of the Endocrine System
3. Types and Mechanisms of Hormonal Action
3.1. Types of Hormones
- Peptide and Protein Hormones
- consist of multiple amino acids that link
to form an amino acid chain.
- Peptide hormones consist of short chains of
amino acids, whereas protein hormones are longer polypeptides.
- Both types are synthesized like other body
proteins: DNA is transcribed into mRNA, which is translated into an amino
acid chain.
- Act on cell surface receptors
- Examples of peptide hormones: insulin, glucagon, ADH
- Examples of protein hormones: GH, FSH
- Steroid hormones
- are derived from the lipid cholesterol.
- Structure: cholesterol derivatives, lipids
- Solubility: lipophilic
- Synthesis: stepwise modification of cholesterol molecule in various
intracellular compartments (in the endocrine gland and also in the blood
and target tissues)
- Storage: hormones not stored, only precursor (cholesterol) stored
- Secretion: diffusion
- Transport: mostly bound to plasma proteins
- Receptor site: inside of target cell
- Action: direct
effects on genes ®
production of new proteins
- e.g., cortisol, estrogen, aldosterone.
- Amino Acid Derivatives (Amine hormones)
- are synthesized from the amino acids
tryptophan or tyrosine
- Catecholamines (dopamine, epinephrine,
and norepinephrine)
- Structure: tyrosine
derivative
- Solubility:hydrophilic
- Synthesis: cytosol
- Storage: secretory
(chromaffin) granules
- Secretion: exocytosis
- ransport: as
a free hormone and bound to plasma proteins
- Receptor site: surface
of target cell
- Action: second
messenger system
- Structure: iodinated
tyrosine derivative
- Solubility: lipophilic
- Synthesis: extracellular
colloid
- Storage: extracellular
colloid
- Secretion: endocytosis
of colloid
- Transport: mostly
bound to plasma proteins
- Receptor site: inside
of target cell
- Action: direct
effects on genes ®
production of new proteins