The gastrointestinal (GI) tract is a continuous tube running from the mouth to the anus, responsible for processing food, absorbing nutrients, and eliminating waste. Medical professionals divide this structure into the upper GI tract and the lower GI tract, primarily for diagnostic and clinical purposes. This division helps localize the source of symptoms, such as bleeding or pain, and determines the most appropriate examination methods.
Defining the Upper GI Tract
The upper GI tract encompasses the organs responsible for the initial stages of digestion and the transit of food from the mouth. This section includes the esophagus, the muscular tube that transports swallowed food down to the stomach. The stomach, a J-shaped organ, then mixes food with acids and digestive enzymes to break it down further.
Following the stomach is the duodenum, the first segment of the small intestine. Here, the initial breakdown of food is completed with the help of bile from the liver and enzymes from the pancreas. The anatomical demarcation separating the upper and lower GI tracts is the Ligament of Treitz, also known as the suspensory muscle of the duodenum. This ligament connects the duodenojejunal flexure—where the duodenum ends and the jejunum begins—to the abdominal wall.
Defining the Lower GI Tract
The lower GI tract begins immediately after the Ligament of Treitz, transitioning into the jejunum and continuing through the ileum, the final and longest segment of the small intestine. The small intestine, extending for approximately 20 feet, is responsible for absorbing nutrients and minerals from digested food.
The tract then enters the large intestine, which includes the cecum, colon, and rectum. The large intestine’s primary function is to absorb water and electrolytes from the remaining indigestible material, transforming liquid contents into solid waste. The colon, divided into ascending, transverse, descending, and sigmoid sections, prepares this waste for storage. The rectum and anus serve as the temporary storage and exit point for stool during elimination.
Common Diagnostic Tests for the Upper GI
When a patient presents with symptoms suggesting an issue in the upper GI tract, medical professionals often use Esophagogastroduodenoscopy (EGD), commonly known as an upper endoscopy. The EGD is a direct visual examination using an endoscope—a thin, flexible tube equipped with a light and miniature video camera. This device is passed through the mouth and down the esophagus, stomach, and into the duodenum.
During the procedure, typically performed under sedation, the specialist examines the lining of these organs for ulcers, inflammation, tumors, or blockages. The endoscope allows the physician to perform therapeutic actions, such as stopping bleeding, or to take tissue samples (biopsies) for laboratory analysis. The procedure usually takes between 15 to 30 minutes.
Another common diagnostic tool for the upper tract is the Barium Swallow, also known as an upper GI series or esophagram. This test uses X-ray technology to visualize the internal structure and function of the esophagus, stomach, and duodenum. The patient drinks a liquid containing barium, a substance that coats the mucosal lining and appears opaque on X-ray imaging.
As the patient swallows the contrast agent, fluoroscopy captures a real-time moving image of the barium traveling through the tract. This dynamic view helps diagnose issues related to swallowing, muscle motility disorders, or structural abnormalities like hiatal hernias or strictures. The Barium Swallow often serves as a complementary tool to the direct visual inspection offered by an EGD.
Common Diagnostic Tests for the Lower GI
The primary procedure for examining the lower GI tract is a Colonoscopy. This examination uses a longer, flexible scope called a colonoscope, which is inserted through the rectum and guided through the entire colon. Colonoscopy is a tool for both screening and diagnosis, allowing the physician to visually inspect the inner wall of the colon and rectum.
The procedure is widely used to screen for colorectal cancer by detecting and removing precancerous growths known as polyps. If polyps or other abnormal tissues are found, the colonoscope is equipped with instruments to remove them or take biopsies. Alternative methods include flexible sigmoidoscopy, which only examines the lower portion of the colon and rectum, and CT colonography, a non-invasive X-ray scan that creates detailed images of the colon’s interior.