Corpus: Duodenum

The duodenum is the most proximal part of the small intestine, located immediately after the stomach.

The name "duodenum" originates from the Greek physician Herophilus, who compared its length to 12 fingers. The medieval Latin name "intestinum duodenum digitorum" was later shortened to "duodenum."

3.1. Structure

The duodenum is approximately 30 cm long, mostly retroperitoneal, and forms a horseshoe shape around the head of the pancreas. It is divided into four parts based on its course and location:

• Superior part: This upper portion lies intraperitoneally, measures about 5 cm, and has an enlarged initial section called the duodenal ampulla or duodenal bulb. It transitions at the superior duodenal flexure into the descending part.
• Descending part: In this segment, the common bile duct and pancreatic duct open into the duodenum at the papilla duodeni major. If an accessory pancreatic duct is present, it opens at the papilla duodeni minor. It transitions at the inferior duodenal flexure into the horizontal part.
• Horizontal part: This lower, horizontal portion crosses in front of the inferior vena cava and abdominal aorta, passing beneath the superior mesenteric artery and vein. It transitions into the ascending part.
• Ascending part: The ascending part ends at the duodenojejunal flexure, where it transitions to the jejunum. Two peritoneal folds, the superior duodenal fold (Treitz ligament) and inferior duodenal fold, form the superior and inferior duodenal recesses at this junction.

3.2. Curvatures

The duodenum contains three key flexures:

• Superior duodenal flexure: between the superior and descending parts
• Inferior duodenal flexure: between the descending and horizontal parts
• Duodenujejunal flexure: between the ascending part and the jejunum (Treitz flexure)

3.3. Vascular supply

3.3.1. Arterial supply

The duodenum is supplied by branches from both the celiac trunk and the superior mesenteric artery. The common hepatic artery gives rise to the gastroduodenal artery, which further branches into:

• Posterior superior pancreaticoduodenal artery and anterior superior pancreaticoduodenal artery, supplying the superior and descending parts.
• Retroduodenal arteries, which originate from the gastroduodenal artery and supply the dorsal parts of the duodenum.

The superior mesenteric artery gives off the inferior pancreaticoduodenal artery, which splits into anterior and posterior branches, supplying the lower sections of the duodenum. These vessels form a double vascular loop around the pancreatic head through anastomoses between the superior and inferior pancreaticoduodenal arteries.

3.3.2. Venous outflow

Venous drainage follows the course of the arteries, with the veins named analogously to the corresponding arteries.

3.3.3. Lymphatic drainage

Lymphatic vessels follow the arteries in the opposite direction, draining into the pancreaticoduodenal lymph nodes and pyloric lymph nodes for the upper sections, and into the superior mesenteric lymph nodes for the lower sections.

3.4. Innervation

3.4.1. Sympathetic innervation

Preganglionic sympathetic fibers reach the duodenum via the greater splanchnic nerve and the celiac ganglion, traveling along periarterial plexuses.

3.4.2. Parasympathetic innervation

Preganglionic parasympathetic fibers run in the posterior vagal trunk. They switch to the second neuron within the intestinal wall.

The duodenum's wall structure is similar to other parts of the small intestine, but with distinctive features such as pronounced Kerckring folds (plicae circulares) and the presence of Brunner's glands, which are unique to the duodenum and are located within its submucosa. These glands produce mucus to protect the duodenum from the acidic chyme entering from the stomach.

The duodenum neutralizes the acidic pH of stomach contents by mixing it with bicarbonate-rich secretions. In addition, it blends chyme with digestive enzymes from the pancreas and duodenal glands. The duodenum also plays a regulatory role in gastric emptying and secretion, as well as in the release of bile and pancreatic juice, through hormonal control. The duodenal epithelium secretes hormones such as secretin and cholecystokinin, which are regulated by factors like the pH and fat content of the chyme.

6.1. Diagnostics

The duodenum is typically examined using endoscopy, specifically gastroduodenoscopy, which allows for both visual inspection and the collection of tissue samples from suspicious areas.

6.2. Diseases

The most common pathological condition of the duodenum is a duodenal ulcer. Malignant tumors of the duodenum are relatively rare. Other conditions include:

• Duodenal atresia
• Duodenal diverticulum

Duodenal stenosis can result from superior mesenteric artery syndrome or superior mesenteric vein syndrome, as well as from other causes.