**Question:** Cervical part of esophagus all are true except-

A. Esophagus is a muscular tube that transports ingested food from the mouth to the stomach.
B. Esophagus has a mucous membrane that protects against gastric acid.
C. Esophagus is innervated by parasympathetic nervous system.
D. Esophagus undergoes peristalsis, a rhythmic muscle contraction, to move food along.

**Correct Answer: Option B (Mucous membrane protects against gastric acid)**

The correct answer is B. The esophagus has a mucous membrane that protects the esophagus from the corrosive stomach acid. This mucous membrane helps neutralize the acid and prevents damage to the esophageal tissue.

The other options are true for the cervical part of the esophagus:

A. The esophagus is a muscular tube that transports food, which is also true.
C. The esophagus is innervated by the parasympathetic nervous system, which is also true.
D. Peristalsis, the rhythmic muscle contractions that aid in food movement, is also true for the esophagus.

However, option B is incorrect because the primary role of the mucous membrane is not to protect against gastric acid but to lubricate, cushion, and facilitate the sliding of food bolus through the esophagus. The esophagus does have intrinsic defenses such as the mucus-secretory glands and bicarbonate-secreting cells that neutralize the stomach acid, making it less corrosive for the esophagus.

In summary, while all options except B are true, option B is incorrect as it inaccurately attributes the function of the esophagus's mucous membrane to a defensive mechanism against gastric acid, when its primary function is to facilitate the movement of food bolus.

**Clinical Pearls:**

1. The esophagus begins at the cricopharyngeal sphincter and ends at the gastroesophageal junction, connecting to the stomach.
2. The primary purpose of the mucous membrane lining is to lubricate, cushion, and aid the sliding of food bolus through the esophagus.
3. The esophagus is innervated by the parasympathetic nervous system, which helps regulate the smooth muscle contractions involved in peristalsis and the relaxation of the lower esophageal sphincter.

4. The esophagus is protected by several defense mechanisms including the production of mucus and bicarbonate ions that neutralize the stomach acid, making the esophagus less susceptible to gastric acid damage. This is the reason why option B is incorrect, as it misattributes the function of the mucous membrane to protect against gastric acid, when its primary function is to facilitate the movement of food bolus.