Osmosis knows that anatomy can be overwhelming, but hopefully this video on the esophagus and stomach can make it a bit easier, so let's begin “digesting” this content together! The esophagus and the stomach are part of the upper digestive tract and are involved in the first phases of digestion. We are going to use the pizza we ate for dinner last night as an example to help us explore the pathway of the esophagus and stomach.
Now, let’s start with the esophagus, which is a muscular tube that carries food from the pharynx to the stomach. We can think about the esophagus as a subway that our food travels in between these two structures. After the pizza we ate has been chewed and swallowed, the muscles of the esophagus help propel the bolus towards the stomach in a wave-like motion called peristalsis.
The esophagus is made up of two muscular layers: an internal circular layer and an external longitudinal layer. In its proximal or superior third, the external layer consists of striated skeletal muscle, which is under voluntary control, while its distal or inferior third is made up of smooth muscle, which is under involuntary control.
And as you’d expect, the middle third is a transitional segment that consists of a mix of both types of muscle. The esophagus follows the curve of the vertebral column as it descends through the neck and into the mediastinum.
Once it reaches the diaphragm, it passes through the esophageal hiatus, just to the left of the median plane at the level of the T10 vertebra, where it becomes the abdominal esophagus. The abdominal esophagus finishes its journey by becoming continuous with the stomach through the cardial orifice, which is surrounded by the cardiac sphincter.
It sits left of the midline at the level of the T11 vertebra and designates the esophagogastric junction, which is an important landmark where the mucosa abruptly changes from the stratified squamous epithelium of the esophagus to the simple columnar epithelium of the stomach.
The right border of the abdominal esophagus continues with the lesser curvature of the stomach, while its left border will eventually continue with the fundus of the stomach.
There are also important points along the length of the esophagus where there are natural constrictions. These constrictions of the esophagus are caused by four structures passing the esophagus as it descends in the cervical, thoracic and diaphragmatic regions.
Now, to better visualize the esophagus and these constrictions, a barium swallow study can be performed which uses an x-ray imaging technique called fluoroscopy. The cervical constriction, also known as the upper esophageal sphincter, is located at the pharyngoesophageal junction and is caused by the cricopharyngeus muscle.
Lastly, the diaphragmatic constriction is where the esophagus passes through the esophageal hiatus of the diaphragm, with the diaphragm actually contributing to the lower esophageal sphincter. These esophageal constrictions are areas where food can potentially get stuck.
Now let’s talk about blood supply! Proximally, the esophagus is supplied by branches of the inferior thyroid arteries. As we move distally, branches of the bronchial arteries and branches coming directly from the thoracic aorta supply the thoracic esophagus. The arterial supply of the abdominal esophagus is provided by the left gastric artery which is a branch of the celiac trunk, and the left inferior phrenic artery.
The venous drainage of the thoracic esophagus occurs via the inferior thyroid vein and tributaries of the azygos vein. The venous drainage of the abdominal esophagus has two routes: to the hepatic portal venous system through the left gastric vein, and into the systemic venous system through esophageal veins entering the azygos vein.
The lymphatic drainage of the esophagus is divided into thirds; the superior third drains into deep cervical lymph nodes, the middle third into superior and posterior mediastinal lymph nodes, and the inferior third into the left gastric lymph nodes.
Lastly, let’s discuss the innervation of the esophagus. It receives parasympathetic fibres from the right and left vagus nerves, and sympathetic fibers from the sympathetic trunks. The vagus nerves go on to form the esophageal plexus, which also contains sympathetic fibers mainly from the greater splanchnic nerves that arise from the sympathetic trunk at the T5 to T9 level.
Its fibers synapse along the aorta - including at the celiac ganglia - before contributing to the esophageal plexus. Let’s take a quick break and try to identify the four anatomical areas of constrictions in the esophagus.
Now, let’s move on to the stomach, the next stop for our bite of pizza after its journey through the esophagus. The stomach acts as a reservoir for ingested food like our piece of pizza, and prepares it for digestion with the help of enzymes and gastric juice which gradually converts solid food into a semiliquid mixture called chyme - we can think about the stomach as our own endogenous food blender.
Now, the size, shape and position of the stomach can vary from person to person and may change even in the same person during movements such as respiration and body position. When lying supine, the stomach can occupy parts of the epigastric region, umbilical region, left hypochondriac region, and left lumbar region of the abdomen. On the other hand, when sitting upright, the stomach will move slightly inferior.
Now that we understand what the stomach does and its position within the body, let's dig into the external anatomical features of the stomach. The stomach has four parts: the cardia, the fundus, the body and the pyloric part, along with two curvatures: the lesser curvature and the greater curvature.
The cardia is the part surrounding the cardial orifice which is the superior opening of the stomach and where the esophagus connects to the stomach. The cardia is located at the level of the T11 vertebra.
The fundus is the dilated superior portion of the stomach and is related to the left dome of the diaphragm. Between the fundus and the esophagus, there’s a deep notch called the cardial notch. The body of the stomach comprises the major portion of the stomach and is located between the fundus and the pyloric antrum.
The pyloric portion of the stomach is a funnel-shaped region which has a wider part called the pyloric antrum and a narrow part called the pyloric canal. Distally, it has a sphincteric region called the pylorus which is a marked thickening of the circular layer of smooth muscle that controls passage of the stomach contents through the pyloric orifice into the duodenum.
In a supine position, the pyloric part is located at the level of the transpyloric plane, located at the L1 vertebra midway between the jugular notch superiorly and the pubic crest inferiorly, while in a standing position, its location varies from the L2 through L4 vertebra.
The lesser curvature of the stomach forms the shorter concave right border of the stomach which is continuous with the right side of the esophagus superiorly. The greater curvature forms the longer convex left border of the stomach, which passes inferiorly and curves medially to reach the pyloric antrum. Because of the unequal lengths of the two curvatures, the stomach is shaped like the letter J.
Let’s take another break and try to identify the parts of the stomach as well as the two curvatures.
- "Clinically Oriented Anatomy, 7e" Wolters Kluwer (2017)
- "Stomach" Radiopaedia (2021)