cell signalling

• Cells need to communicate with each other to control processes inside the body and to respond to changes in the environment. Cells communicate with each other by cell signalling, which uses messenger molecules.
• • Cell signalling starts when one cell releases a messenger molecule (e.g. a hormone).
  • This molecule travels to another cell (e.g. in the blood).
  • The messenger molecule is detected by the cell because it binds to a receptor on its cell membrane.
  • The binding then triggers a change in the cell, e.g. a series of chemical signals is set off.
• The cell membrane is important in the signalling process. Proteins in the cell membrane act as receptors for messenger molecules. These receptor proteins are called 'membrane-bound receptors'.
• • Receptor proteins have specific shapes - only messenger molecules with a complementary shape can bind to them.
  • Different cells have different types of receptors - they respond to different messenger molecules.
  • A cell that responds to a particular messenger molecule is called a target cell.
• Many messenger molecules are hormones. Hormones work by binding to receptors in cell membranes and triggering a response in the cell.
• Glucagon is a hormone that's released when there isn't enough glucose in the blood. It binds to receptors on liver cells, causing the liver cells to break down stores of glycogen to glucose.
• FSH is a hormone that's released by the pituitary gland during the menstrual cycle. It binds to receptors on cells in the ovaries, causing an egg to mature ready for ovulation.
• Many drugs work by binding to receptors in cell membranes. They either trigger a response in the cell, or block the receptor and prevent it from working. Understanding how cells communicate using membrane-bound receptors is important in the development of medicinal drugs - the receptors can be used as sites for targeted action.
• The body produces chemicals called endorphins, to relieve pain.

  Endorphins bind to opioid receptors in the brain and reduce the transmission of pain signals. Morphine is a drug used to relieve pain.

  It works by binding to the same opioid receptors as endorphins, also triggering a reduction in pain signals.
• Cell damage causes the release of a chemical called histamine. Histamine binds to receptors on the surface of other cells and causes inflammation. Antihistamines work by blocking histamine receptors on cell surfaces. This prevents histamine from binding to the cell and stops inflammation.