The mechanism of hormone action on the target organ/ tissue/cell can be understood as follows:
Hormone receptors: Hormone receptors are specific proteins which are present on the cell membrane or inside the cell.
- Hormone receptors on the cell membrane are called membrane bound receptors.
- Hormone receptors present inside the cell are called intracellular hormone receptor and are mostly present in the nucleus hence called nuclear receptors.
The union of hormone and receptor forms a complex called hormone - receptor complex. Each hormone binds to a specific receptor. i.e., this is hormone/receptor specific. This complex formation leads to certain biochemical change in the target tissue. The target tissue’s metabolism and physiological function are thus, regulated by hormones. Those hormones which are bound to the membrane receptors normally do not enter the target cell, but instead generate a second messengers e.g., cyclic AMP, IP3, Ca++ etc. Which in turn regulate the metabolism of the cell.
The hormones that enter the cell and interact with the intracellular receptors e.g., steroid hormones, iodothyronines etc. These results in mostly regulation of gene expression/chromosome function by the interaction of hormone receptor complex with the genome. Cumulative biochemical action results in the physiological and developmental effects in the individual.
