**Core Concept**
Deglutition peristalsis is a type of peristaltic movement in the esophagus that occurs during swallowing. It is a coordinated, wave-like contraction of the esophageal muscles that propels food from the pharynx into the stomach. This process is essential for the normal transit of food through the esophagus.

**Why the Correct Answer is Right**
During deglutition, the process begins with the initiation of the swallow reflex, which triggers a series of electrical impulses that travel down the esophagus. These impulses stimulate the smooth muscle cells in the esophageal wall to contract in a coordinated manner, creating a peristaltic wave that moves food downwards. The peristaltic wave is mediated by the release of acetylcholine from the parasympathetic nervous system, which binds to muscarinic receptors on the esophageal smooth muscle cells, causing them to contract.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the mechanism of deglutition peristalsis. While the myenteric plexus is involved in regulating esophageal motility, it is not the primary mechanism responsible for deglutition peristalsis.
**Option B:** This option is incorrect because it is not a specific mechanism of deglutition peristalsis. The release of gastrin is not directly involved in the process of swallowing.
**Option C:** This option is incorrect because it is not a characteristic of deglutition peristalsis. The esophageal muscles do not relax during deglutition; instead, they contract in a coordinated manner to propel food downwards.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that deglutition peristalsis is a reflexive process that is triggered by the swallow reflex. This process is essential for the normal transit of food through the esophagus, and any disruption to this process can lead to swallowing disorders, such as dysphagia.

**Correct Answer: D. Esophageal smooth muscle contraction.**