In paracrine signaling, where do signaling molecules act?

• A. They act on distant tissues via the bloodstream.
• B. They act on neighboring cells in close proximity.
• C. They act inside the same cell.
• D. They diffuse to all body tissues equally.

Answer: (B)

Paracrine signaling involves local action: a cell releases signaling molecules that diffuse through the extracellular fluid to neighboring cells in the same tissue. Because these mediators travel only short distances and are often degraded quickly, their effects stay near the source rather than spreading throughout the body. This is different from endocrine signaling, where messengers enter the bloodstream to reach distant tissues; it’s also different from autocrine signaling, where a cell responds to its own secreted signals; and it isn’t a global diffusion to all tissues.