Upper GI Tract
The upper digestive tract consists of the
- pharynx (throat),
- stomach, and
- duodenum (first part of the small intestine).
Your mouth is the first part of your digestive tract. It is where food is chewed and mixed with saliva until it becomes a soft mass that can be swallowed. Saliva is released into the mouth even before food enters itthe odor or thought of food can make you salivate. An enzyme in saliva called amylase starts breaking down the carbohydrates from food in your mouth. When you swallow, food moves into your pharynx, a passageway that is 5 inches long and carries both food and air.
From the throat, food enters the esophagusa hollow, muscular tube about 10 inches long. At the upper end of the esophagus is a circular area of muscle tissue called the upper esophageal sphincter. When you swallow, this sphincter relaxes to allow food to enter the esophagus.
After you swallow, the sphincter contracts to prevent air in the throat from entering the esophagus. A structure called the epiglottis closes over the trachea to prevent the food from entering the airways or lungs. Peristalsis pushes food through your esophagus.
The esophagus descends into the stomach through an opening in the diaphragm (a thin muscle that separates your chest cavity from your abdominal cavity). At the lower end of the esophagus is a ring of muscle tissue called the lower esophageal sphincter. When food approaches, the lower esophageal sphincter relaxes to allow food to pass through to the stomach. It then contracts to prevent reflux (the backflow of stomach contents into the esophagus).
The esophagus contains a protective inner lining called the mucosa. In a healthy esophagus, the mucosa is smooth and pink. The place where the esophagus makes contact with the stomach is called the gastroesophageal junction; it forms an irregular white line called the Z-line that can be seen by your doctor with an endoscope.
Stomach and Duodenum
Your stomach is a large, stretchy bag located slightly to the left in the upper portion of your abdomen. Its function is to hold ingested food and to continue the digestive process that began in your mouth by secreting gastric acid and digestive enzymes. Your stomach has four sections:
- the cardia, a short part next to the gastroesophageal junction
- the fundus, the top of the stomach located under the left dome of the diaphragm
- the body, the largest portion of the stomach located between the fundus and the antrum
- the antrum, a short, channel-like portion near the outlet of the stomach
The pylorus is a circular muscle below the antrum that connects the outlet of the stomach with the duodenum. The duodenum, the first portion of the small intestine, is a C-shaped tube that curves around the head of the pancreas. The part of the duodenum closest to the stomach is called the duodenal bulb.
Farther along in the duodenum is the major duodenal papilla, a protuberance where the common bile duct and main pancreatic duct enter the duodenum. The common bile duct carries bile secreted from the liver after it is stored in the gallbladder into the duodenum; the main pancreatic duct carries enzymes formed in the pancreas. The bile and pancreatic enzymes help digest food in the duodenum.