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The esophagusThe muscular tube that transports food from the pharynx to the stomach via peristalsis. is a muscular tube that connects the pharynxThe muscular passageway connecting the mouth to the esophagus and larynx. to the stomach. It propels food from the mouthThe opening of the digestive tract where food enters and mastication begins. to the stomach through peristaltic contractions.
Mucosa
The esophagus is a hollow tube through which a bolusA rounded mass of food mixed with saliva that is ready for swallowing. of food moves. When not in use the esophagus collapses, producing folds in the mucosaThe innermost lining of the digestive tract that contains mucus-secreting cells for protection and a. The epithelium lining the esophagus is composed of stratified squamous epithelial cellsThe basic structural and functional units of life.. The epithelium of the esophagus is non-keratinized, but there are keratinized patches in the superiorAbove or toward the upper part of the body. portion by the pharynx. These waterproofed patches are not necessary as we move inferiorly into the esophagus towards the stomach. The multiple layers of squamous cells can shed due to mechanical abrasion. This is caused by the food bolus scraping along the sides as it descends to the stomach.
Submucosa
The submucosa of the esophagus is made largely of areolar and dense irregular connective tissues. In the superior portion of the esophagus, submucosal glandsGlands in the airway walls that secrete mucus. secrete an alkaline mucus substance. This helps in lubricating the passage of the bolus. These glands become more numerous in the inferiorBelow or toward the lower part of the body. portion of the esophagus. Glands secrete mucus with a more neutralA solution with a pH of 7. pHA measure of hydrogen ion concentration in a solution.. This mucus protects the esophagus from acidicA solution with a pH below 7, having a higher concentration of H⁺ ions. gastric juices. This protection is needed in the inferior portion of the esophagus.
Muscularis Externa
The muscularis externaA smooth muscle layer of the digestive tract responsible for peristalsis and segmentation. is the layer of smooth muscle. It is responsible for peristaltic contractions. These contractions propel food through the esophagus and into the stomach. It consists of inner circular layers of smooth muscle fibers. It also contains outer longitudinal layers. These fibers contract sequentially to create wave-like movements (peristalsis Rhythmic contractions of smooth muscle that move food through the digestive tract.). To complete the peristaltic contractions, the inner circular layer contracts in an alternating pattern with the longitudinal layer. These alternating contraction propel the food through the expanded tube of the esophagus. In the superior portion of the esophagus, parts of the muscularis externa are skeletal muscle. They transition to smooth muscle in the inferior esophagus.
Serosa
The outermost layer of the esophagus is the adventitiaThe outermost connective tissue layer of an organ, such as the esophagus, which binds it to surround. It is a dense layer of connective tissue that surrounds the muscularis externa. This layer provides structural support to the esophageal wall. This adventitia is thicker than the serosa covering the GI tract inferior to the diaphragm. The thicker adventitia aids in protecting other critical organs in the thoracic cavityThe body cavity housing the heart and lungs.. These organs include the heart and lungs. In the abdominal portion of the esophagus, it pierces the diaphragm at the esophageal hiatus. There, the outermost layer is covered by serosa. This serous membrane is derived from the peritoneumThe membrane lining the abdominal cavity and organs..
Specializations
There are specialized muscular structures called sphincters at both ends of the esophagus. These sphincters regulate the passage of food into and out of the esophagus. The upper esophageal sphincter (UES) controlsVariables that remain constant to ensure a fair test. food passage from the pharynx into the esophagus. The lower esophageal sphincter (LES or cardiac sphincter) manages food movementA fundamental property of life involving motion of the body or its parts. from the esophagus into the stomach. It also prevents gastric contents from refluxing into the esophagus. If this sphincter malfunctions, it can allow gastric juices to “reflux” into the esophagus. The mucosa is not prepared for this acidity. Barrett’s esophagus is a pre-cancerous condition. The stratified squamous cells of the esophagus elongate. They become cuboidal and columnar to resist the erosion from the gastric juices.
The esophagus pierces the diaphragm at the esophageal hiatus. When the fundic portion of the stomach pushes through this hole, it is called a hiatal hernia. Hiatal hernias reduce the volume the stomach can hold. This leads to early satiation. You may feel like you have eaten enough food. This early feeling of fullness leads to lower consumption of calories and malnutrition.
Figures 1-4: Esophagus, H&E, 20X Slide 153
Figure 5: gastro-esophageal junction H&E longitudinal, 40X Slide155
All by University of Michigan Histology, licensed under CC BY-NC-SA 3.0.
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List of terms
- esophagus
- pharynx
- mouth
- bolus
- mucosa
- cells
- superior
- submucosal glands
- inferior
- neutral
- pH
- acidic
- muscularis externa
- peristalsis
- adventitia
- thoracic cavity
- peritoneum
- controls
- movement