To better understand gastrointestinal bleeding, it helps to understand the anatomy of the gastrointestinal tract.

The esophagus is a muscular tube that pushes food to the stomach. The stomach is a large pouch that receives food from a meal. The stomach slowly pushes the food into the small intestine, which absorbs nutrients from the food.

Food passes through the small intestine and into the large intestine, which absorbs water from the food. The small intestine is about 18 feet (3.5 m) long and the large intestine is about 5 feet (1.5 m) long.

The small intestine has three parts:

• Duodenum:
• Connects to the stomach
• Jejunum:
• Middle portion of the small intestine
• Ileum:
• Lower portion of the small intestine that connects to the cecum (first part of the large intestine)

The large intestine is also known as the colon. It is the last portion of the intestine.

The colon has several parts, including:

• Cecum:
• The portion of the colon that connects to the ileum (small intestine). The appendix is a finger-like pouch that comes off of the cecum.
• Ascending colon:
• The first section after the small intestine, located on the right side
• Transverse colon:
• Sits horizontally across the upper abdomen
• Descending colon:
• Located on the left side of the abdomen
• Sigmoid:
• A short, S-shaped section above the rectum
• Rectum:
• The lowest internal part of the colon

Gastrointestinal anatomy:

• Esophagus and stomach
• Intestines
• Blood vessels of the intestines
• Entire gastrointestinal tract