Summary:
- Hormones are the messenger molecules of the endocrine system.
- Endocrine hormones travel throughout the body in the blood.
- Each hormone affects only certain cells, called target cells.
- A target cell is affected by a particular hormone because it has receptor proteins that are specific to that hormone.
- A hormone travels through the bloodstream until it finds a target cell with a matching receptor it can bind to.
- When the hormone binds to a receptor, it causes a change within the cell.
- Exactly how this works depends on whether the hormone is a steroid hormone or a non-steroid hormone.