Cell Signaling and Chemical Messengers

Living cells rarely act in isolation. From a single-celled organism sensing nutrients to the billions of cells in your body coordinating a heartbeat, life depends on communication. Cell signaling is the process by which cells detect and respond to chemical messages in their environment. This lesson introduces the vocabulary and logic of signaling, which underlies almost every regulatory system you will meet in biology.

Chemical messengers and their range

Cells communicate using chemical messengers called ligands. These messengers differ in how far they travel:

• Endocrine signaling uses hormones released into the bloodstream, reaching distant target cells throughout the body. Insulin from the pancreas is a classic example.
• Paracrine signaling affects nearby cells; the messenger diffuses onl