Duodenum

The first section of the small intestine in most higher vertebrates, including humans

The duodenum is the first section of the small intestine in most higher vertebrates, including humans. It plays a crucial role in the digestive process by receiving partially digested food from the stomach and beginning the absorption of nutrients.

Anatomy

The duodenum is approximately 25 to 30 centimeters (10 to 12 inches) long and is shaped like a "C". It is located just below the stomach and is connected to the pylorus, the opening from the stomach into the duodenum. The duodenum is divided into four parts:

First Part

The first part, also known as the superior part, is about 5 centimeters long. It begins at the pylorus and extends to the neck of the gallbladder. This section is intraperitoneal and is the most mobile part of the duodenum.

Second Part

The second part, or descending part, is about 7 to 10 centimeters long. It runs vertically downward in front of the right kidney. This section receives the bile and pancreatic juice through the major duodenal papilla.

Third Part

The third part, or horizontal part, is about 10 centimeters long. It crosses horizontally from right to left, passing in front of the inferior vena cava, the aorta, and the vertebral column.

Fourth Part

The fourth part, or ascending part, is about 2.5 centimeters long. It ascends on the left side of the aorta to the level of the second lumbar vertebra, where it turns abruptly forward to become the jejunum.

Function

The duodenum plays a vital role in the digestive process. It is responsible for:

• Receiving chyme from the stomach and neutralizing its acidity.
• Mixing chyme with bile and pancreatic juices to aid in digestion.
• Beginning the absorption of nutrients such as iron and calcium.

The duodenum's lining contains Brunner's glands, which secrete an alkaline mucus that helps to neutralize gastric acid in the chyme.

Clinical Significance

The duodenum can be affected by various medical conditions, including:

• Duodenal ulcers: These are sores that develop on the lining of the duodenum due to excessive acid production or infection with Helicobacter pylori.
• Celiac disease: An autoimmune disorder where ingestion of gluten leads to damage in the small intestine, including the duodenum.
• Duodenitis: Inflammation of the duodenum, often caused by infection or irritation from stomach acid.

Images

File:Duodenum anatomy.png

Diagram of the duodenum showing its four parts.

The duodenum is part of the digestive system, connecting the stomach to the jejunum.

Related Pages

• Small intestine
• Digestive system
• Pancreas
• Bile duct