How do the Stomach and Esophagus Process Food?
The food you eat makes its way to your stomach via the esophagus. It officially enters the abdomen when it passes through the esophageal hiatus of the diaphragm. The esophagus ends at the esophagogastric junction, where it joins the stomach.
The digestive tract runs from the mouth to the anus and includes part of the esophagus, the stomach, the small intestine, and part of the large intestine.
In the abdomen, the esophagus is located just to the left of the midline of the body near the level of the 11th thoracic vertebra. It’s also located behind the peritoneum, so it’s considered to be retroperitoneal.
The esophagus has two layers of muscle, a circular layer internally and an external layer that runs from one end to the other longitudinally. In the upper part of the esophagus, the outer layer of muscle is skeletal muscle, whereas the external layer of the lower part of the esophagus is smooth muscle.
The lining of the esophagus is different than the lining of the stomach, and the area of transition between the two is called the Z line. The inferior esophageal sphincter (tight ring of muscle) is located just superior to (above) this line.
The esophageal sphincter opens to allow food and liquid to enter the stomach; otherwise it remains shut. Gastroesophageal reflux disease (you may know it as GERD or acid reflux) results when the sphincter frequently remains open, allowing the acidic stomach juices to flow into the lower part of the esophagus, which is painful and can result in damage to the tissues that line the esophagus.
Innervation of the esophagus comes from the anterior and posterior gastric nerves (vagal trunks) and the greater splanchnic nerves (thoracic sympathetic trunks). The esophagus receives blood flow from the esophageal branches of the left gastric artery and from the left inferior phrenic artery. Venous blood is drained by the left gastric vein of the portal system and into the esophageal veins that drain into the azygos vein. Lymph drains into the left gastric lymph nodes, which drain into the celiac lymph nodes.
The stomach is a muscular bag that holds food and mixes it with digestive juices. The stomach is covered by peritoneum except for areas where blood vessels run along its exterior and a small area posterior to the cardial orifice. It’s located left of the midline of the body in the upper part of the abdominal cavity. The lesser curvature forms the right concave (inwardly curving) margin of the stomach. The greater curvature forms the left convex (outwardly curving) margin of the stomach.
The stomach has a slightly different shape in each person, but it is divided into the same parts:
Cardia: The cardia surrounds the cardial orifice, which is where the esophagus joins the stomach.
Cardial notch: The cardial notch is located between the esophagus and the fundus.
Fundus: The fundus is the superior portion of the stomach. It begins at the top of the stomach (just underneath the left dome of the diaphragm) and ends at a plane at the level of the cardial orifice.
Body: The body is the major part of the stomach between the fundus and the pyloric antrum.
Pyloric portion: The pyloric portion of the stomach forms the rest of the stomach and ends with the pyloric orifice that opens into the duodenum. The widest part is called the pyloric antrum, and the narrower part of the funnel-shape is the pyloric canal. The pylorus has a thickened layer of smooth muscle that works like a sphincter to control the release of stomach contents into the small intestine.
The interior part of the stomach has rugae that appear when the stomach muscle tissue is contracted.
Parasympathetic innervation is provided by the anterior vagal trunk, which is from the left vagus nerve, and by the posterior vagal trunk, which comes from the right vagus nerve. Sympathetic nerve supply comes from the celiac plexus.
The short gastric arteries supply blood to the fundus, and the right and left gastric arteries and the right and left gastro-omental arteries supply the rest of the stomach. Veins that drain the stomach include the left and right gastric veins, the short gastric veins, the left gastro-omental veins, and the right gastro-omental vein. The veins drain into the hepatic portal circulation.
Lymphatic vessels follow the arteries and drain lymph into the gastric lymph nodes, gastro-omental lymph nodes, pancreaticosplenic lymph nodes, pyloric lymph nodes, and pancreaticoduodenal lymph nodes. Lymph from these nodes passes to the celiac lymph nodes located near the celiac trunk.
From there, the food travels into the small intestine.