The hormones are classified into four categories :
Amino acid derivative: The hormones epinephrine
and norepinephrine secreted by the adrenal
medulla and thyroxine hormone are derived from
the amino acid tyrosine.
(b) Peptide hormone : The hormones oxytocin and vasopressin secreted by the posterior lobe of pituitary glands are composed of peptides.
(c) Polypeptide hormones : The hormones (like somatotropic, thyrotropic etc.) secreted by anterior lobe of pituitary gland, insulin, glucagon hormones secreted by pancreas are made up of polypeptides.
(d) Steroid hormones : The hormones secreted by
adrenal cortex, testes and ovaries are composed of steroids.