Modes of intercellular communication — defining paracrine signaling In paracrine signaling, a cell releases a chemical messenger that affects which targets?

Introduction:
Cells communicate through endocrine, paracrine, autocrine, and synaptic modes. Paracrine signaling is characterized by local action in the tissue microenvironment rather than systemic distribution through the blood.

Given Data / Assumptions:

• Paracrine mediators diffuse short distances in extracellular fluid.
• They are often rapidly degraded or taken up, limiting range.
• Endocrine signals, in contrast, travel via the bloodstream to distant organs.

Concept / Approach:

Define each mode and match the definition: paracrine targets nearby cells; autocrine targets the same cell; endocrine targets distant cells; synaptic targets are across specialized junctions. The local nature of paracrine action makes Option A correct.

Step-by-Step Solution:

Verification / Alternative check:

Examples include prostaglandins, nitric oxide, and growth factors acting within tissues, observed in developmental biology and inflammation.

Why Other Options Are Wrong:

Option B describes endocrine signaling.

Option C conflates endocrine with paracrine.

Option D describes no signaling; autocrine is signaling to the same cell, not “no cells.”

Option E refers to synaptic signaling, not general paracrine diffusion.

Common Pitfalls:

Confusing paracrine with endocrine simply because both involve secreted factors.

Final Answer:

Only target cells close to the cell from which it was secreted