Which signaling mechanism involves the hormone remaining bound to the adjacent target cell?

• A. Juxtracrine
• B. Paracrine
• C. Autocrine
• D. Endocrine

Answer: (A)

Juxtacrine signaling occurs when the signaling molecule is bound to the surface of the sending cell and directly interacts with a receptor on an adjacent cell that is in contact. Because the signal remains attached to the first cell and does not diffuse away, its effect is limited to the neighboring cell that touches the signaling cell. This is why it matches the idea of the hormone staying bound to the adjacent target cell.

In contrast, paracrine signaling involves secreted factors that diffuse through the extracellular fluid to nearby cells; autocrine signaling targets the same cell that released the signal; endocrine signaling releases hormones into the bloodstream to reach distant targets.