Okay, let's tackle this question about Substance P and its role in peripheral pain. The question is asking which option correctly identifies how Substance P is increased in response to peripheral pain. The correct answer is probably related to the release from sensory nerves.

First, I need to recall what Substance P does. It's a neuropeptide involved in transmitting pain signals. It's stored in the central and peripheral terminals of sensory neurons. When there's peripheral pain, these neurons release Substance P into the synapse. So the mechanism would involve the activation of nociceptors, which are the pain-sensing nerve endings.

Wait, the question is about the peripheral response. So when peripheral tissue is injured, the nociceptors are activated, leading to the release of Substance P. This causes vasodilation and increased vascular permeability, contributing to inflammation. The release is probably mediated by the activation of the C-fibers, which are unmyelinated and transmit slow, persistent pain.

Looking at the options, the correct answer should be the release from C-fiber nociceptors. The other options might include things like release from A-delta fibers, mast cells, or other sources. A-delta fibers are myelinated and transmit sharp, fast pain, but they might not be the main source of Substance P. Mast cells release histamine, not Substance P.

Clinical pearl: Remember that Substance P is part of the tachykinin family and is involved in neurogenic inflammation. It's a key player in chronic pain states. The clinical correlation here is understanding the peripheral mechanisms of pain signaling and how Substance P contributes to the inflammatory response.

**Core Concept**
Substance P is a neuropeptide released from **C-fiber nociceptors** in response to peripheral pain. It mediates neurogenic inflammation via vasodilation and increased vascular permeability. Key to understanding is the role of **tachykinin receptors (NK1)** in pain signaling.

**Why the Correct Answer is Right**
Peripheral pain activates **unmyelinated C-fibers**, which release Substance P from their peripheral terminals. This triggers **NK1 receptor activation** on endothelial cells, causing vasodilation and mast cell degranulation. Substance P also sensitizes nociceptors, amplifying pain signals—a hallmark of **inflammatory pain**.

**Why Each Wrong Option is Incorrect**
**Option A:** Mast cells release histamine, not Substance P.
**Option B:** Aδ-fibers mediate fast, sharp pain but do not release Substance P.
**Option C:** Sympathetic nerves release norepinephrine; they are not primary sources of Substance P.

**Clinical Pearl / High-Yield Fact**
Substance P is a **classic target for analgesics** (e.g., NK1 receptor antagonists). Remember: **"C-fibers = Substance P = slow, burning pain + inflammation."** Avoid confusing with Aδ-fiber-mediated acute pain.

**Correct Answer: C. Release from C-fiber nociceptors**

✓ Correct Answer: D. Nerve terminals