Hormone action:

Any hormone that causes changes in the target cell does not directly act on the cellular structure. First the hormone combines with receptors present in the target cells to form hormone-receptor complex. This complex then induces various changes or reactions in the cells.

Hormone receptors:

The hormone receptors are situated either in the cell membrane, cytoplasm or nucleus of the cells. Therefore according to their situation they are classified as:

1. Cell membrane receptors: They are present in the cell membrane and especially attach the protein hormones like insulin, glucagon.
2. Cytoplasmic receptors: They are present in the cytoplasm of the cell and act as receptor for steroid hormones.
3. Nuclear receptors: They are present in the nuclear membrane and act as receptor for thyroid hormones.