Mechanism of Hormone Action:
Hormones produce their effects on target tissues by binding to receptor proteins present in the target tissues.
On the basis of chemical nature, hormones are divided into:
- Peptide, polypeptide & protein hormones: Insulin, Glucagon, Pituitary hormones, Hypothalamic hormones.
- Steroids: Cortisol, Testosterone, Progesterone, Estrogen.
- Iodothyronines: Thyroid hormones.
- Amino acid derivatives: Epinephrine.
Mode of Hormone Action:
- Non-steroid hormones: They are amino acid, peptides & protein hormones. As they are water soluble & lipid insoluble, they cannot pass through the cell membrane. So, they act through second messengers.
- Steroid hormones: They are lipid soluble, and can pass through the cell membrane. So they directly enter the cell. The only exception being Thyroid hormones that are amine derivatives but are lipid soluble.