4.1.1 Cell communicate by sending & receiving chemical messengers called signaling molecules

Ligands 配体 binds to specific receptor proteins when there is a complementary between molecular shape & electro signs

4.1.2 Cells can communicate over various distances

1. Autocrine: Sending & receive by itself(自言自语)
2. Paracrine: to others (说话)
3. Juxtacrine: Gap junction (肢体接触)
4. Endocrine: information send through circulatory system (打电话)

4.1.3 Communication among cells, tissues & organs underlies homeostasis