Question 11: Which of the following mechanisms is used by the marked structure to influence neighboring cells?
- A. Nerve mediated
- B. Vein mediated
- C. Paracrine (Correct Answer)
- D. Autocrine
Explanation: ***Paracrine***
- The image displays an **Islet of Langerhans** (endocrine component) embedded within the **exocrine acini** of the pancreas. Hormones released from the islet cells act on the adjacent acinar cells, which is a classic example of **paracrine signaling**.
- Specifically, **insulin** released from islet beta cells potentiates exocrine enzyme secretion, while **somatostatin** from delta cells inhibits both endocrine and exocrine secretions locally.
- **Paracrine signaling** involves secretion of signaling molecules that affect nearby target cells in the local environment.
*Incorrect: Nerve mediated*
- Although the pancreas is innervated by the **autonomic nervous system** which regulates both endocrine and exocrine functions, this is not the mechanism by which islet cells *directly* influence their immediate neighboring acinar cells.
- Nerve-mediated control involves neurotransmitters released from nerve endings, not signaling molecules released from the islet cells themselves to act on adjacent acini.
*Incorrect: Vein mediated*
- This describes **endocrine signaling**, where hormones enter the bloodstream to act on distant target organs. While islet hormones do enter veins for systemic effects, their influence on *neighboring cells* is through local diffusion (paracrine), not via the circulation.
- The pancreas has a unique **islet-acinar portal system** where blood from islets perfuses the surrounding acini, but the direct local signaling mechanism is paracrine.
*Incorrect: Autocrine*
- **Autocrine signaling** refers to cells responding to signaling molecules they themselves secrete. For example, some islet cells may respond to their own insulin or glucagon.
- However, the question asks about influencing *neighboring cells* (acinar cells), not self-stimulation, making paracrine the correct mechanism.