Hormones can affect cells directly through intracellular hormone receptors or indirectly through plasma membrane hormone receptors Amino acid-derived hormones are relatively small molecules and include the adrenal hormones epinephrine and norepinephrine.

Peptide hormones are polypeptide chains or proteins and include the pituitary hormones, antidiuretic hormone (vasopressin), and oxytocin Lipid-derived hormones are structurally similar to cholesterol and include steroid hormones such as estradiol and testosterone.

oxytocin — hormone released by the posterior pituitary to stimulate uterine contractions during childbirth and milk let-down in the mammary glands. norepinephrine — hormone released by the adrenal medulla in response to a short-term stress hormone production by the gonads. epinephrine — hormone released by the adrenal medulla in response to a short term stress. plasma membrane hormone receptor — a hormone receptor on the surface of the plasma membrane of a cell.