Motility in the upper third of the oesophagus is decreased in all except-
**Core Concept**
The question tests the understanding of oesophageal motility disorders, specifically focusing on the upper third of the oesophagus. Oesophageal motility is controlled by the **swallowing reflex**, which involves the coordination of **skeletal muscle** in the upper oesophagus and **smooth muscle** in the lower oesophagus.
**Why the Correct Answer is Right**
Without the specific options, the general approach to this question involves understanding that the upper third of the oesophagus is primarily composed of **skeletal muscle** and its motility is controlled by the **cranial nerves**, particularly the **vagus nerve**. Disorders affecting this region can lead to decreased motility.
**Why Each Wrong Option is Incorrect**
**Option A:** Would be incorrect if it suggested a condition that universally decreases motility in the upper oesophagus.
**Option B:** Might be wrong if it proposed a disorder that doesn't typically affect the upper third's motility.
**Option C:** Could be incorrect if it mentioned a condition known for reducing motility in this specific region.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that **oesophageal motility disorders** can significantly impact quality of life, and understanding their pathophysiology is crucial for diagnosis and treatment.
**Correct Answer:** D.