**Core Concept**
The lesser omentum is a double-layered fold of peritoneal tissue that attaches the liver to the stomach, the first part of the duodenum, and the proximal part of the pancreas. It contains blood vessels and nerves that supply these abdominal organs.

**Why the Correct Answer is Right**
The lesser omentum contains the portal vein, the hepatic artery proper, and the common bile duct (CBD), which are the structures that run from the liver to the duodenum. These structures are responsible for the transport of blood, oxygen, and bile between the liver and the intestines. The portal vein carries blood from the gastrointestinal tract and spleen to the liver for detoxification and nutrient processing.

**Why Each Wrong Option is Incorrect**
**Option A:** The lesser omentum does not contain the greater splanchnic nerves, which are actually associated with the greater omentum.
**Option B:** The lesser omentum does not contain the splenic vein, which is actually located in the greater omentum and drains into the portal vein.
**Option C:** The lesser omentum does not contain the left gastric artery, which is actually located in the greater omentum and supplies the stomach.

**Clinical Pearl / High-Yield Fact**
The lesser omentum is a critical anatomical structure that surgeons must consider when performing procedures such as liver transplantation or gastric resection.

**Correct Answer: D.**