Which statement best describes paracrine signaling?

Which statement best describes paracrine signaling?

• A. Ligands secreted into the bloodstream by distant cells.
• B. Ligands secreted by neighboring cells.
• C. Ligands bind DNA directly.
• D. Signals transmitted through gap junctions only.

Answer: (B)

Paracrine signaling is local cell communication where a cell releases signaling molecules into the surrounding extracellular space and those molecules diffuse to nearby cells in the same tissue, triggering responses there. The statement that ligands are secreted by neighboring cells fits this local, short-range mode of communication. If the signal were carried all the way through the bloodstream to distant cells, that would be endocrine signaling, not paracrine. If a signal acted by binding directly to DNA, that’s not how paracrine signaling works—the signaling molecules typically bind to receptors on target cells to start a cascade. And signaling through gap junctions involves direct cytoplasmic transfer between adjacent cells, a different form of communication from the extracellular diffusion seen in paracrine signaling.

Paracrine signaling is local cell communication where a cell releases signaling molecules into the surrounding extracellular space and those molecules diffuse to nearby cells in the same tissue, triggering responses there. The statement that ligands are secreted by neighboring cells fits this local, short-range mode of communication.

If the signal were carried all the way through the bloodstream to distant cells, that would be endocrine signaling, not paracrine. If a signal acted by binding directly to DNA, that’s not how paracrine signaling works—the signaling molecules typically bind to receptors on target cells to start a cascade. And signaling through gap junctions involves direct cytoplasmic transfer between adjacent cells, a different form of communication from the extracellular diffusion seen in paracrine signaling.