**Core Concept**
Cushing ulcers are a type of stress-induced gastric mucosal damage that occurs due to prolonged exposure to stress hormones, particularly cortisol. They are a complication of Cushing's syndrome or can occur in critically ill patients.

**Why the Correct Answer is Right**
Cushing ulcers typically occur in the upper stomach (gastric body), but they can also be found in the lower stomach (antrum) and the duodenum. The pathophysiology involves increased gastric acid secretion, impaired mucosal defense, and reduced blood flow to the gastric mucosa. The stress response leads to the release of cortisol, which in turn stimulates the release of gastric acid.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not a common site for Cushing ulcers. The stomach is the primary site, and the rest of the small intestine is less commonly affected.

**Option B:** This option is incorrect because it is a possible location for Cushing ulcers. The duodenum can be involved in the disease process.

**Option C:** This option is incorrect because it is not a common site for Cushing ulcers. The duodenum is a possible location, but the jejunum is less commonly affected.

**Clinical Pearl / High-Yield Fact**
Cushing ulcers are often associated with other complications of stress, such as gastritis, pancreatitis, and stress-induced bleeding. The diagnosis is typically made on endoscopic examination, and treatment involves addressing the underlying cause of stress.

**Correct Answer:** D.