Cellular signals can be classified into different types based on the distance they travel and their mode of action:
1. Autocrine signaling: The cell releases a signal that acts on itself. 2. Paracrine signaling: The signal affects nearby cells. 3. Endocrine signaling: Hormones travel through the bloodstream to act on distant cells. 4. Juxtacrine signaling: Requires direct contact between cells.
