| Define hormones | Chemical substances that act like messenger molecules in the body. |
| Define receptors | A molecule inside or on the surface of a cell that binds to a specific substance and causes a specific effect in the cell. |
| Define the circulatory system | The system that contains the heart and the blood vessels and moves blood throughout the body |
| Define the lymphatic system | The lymphatic system is our body's 'sewerage system'. It maintains fluid levels in our body tissues by removing all fluids that leak out of our blood vessels. |
| Define upregulation | An increase in the number of receptors on the surface of target cells, making the cells more sensitive to a hormone or another agent. |
| Define downregulation | The process of reducing or suppressing a response to a stimulus |
| Define signal transduction | The process by which a cell responds to substances outside the cell through signalling molecules found on the surface of and inside the cell. |
