What is the esophagus?
- A muscular tube
- Measures 25 cm in length
- Extends from the pharynx to the stomach
Describe the mucosa of the esophagus.
- Stratified squamous
- Protects the esophagus from friction as food travels from the oral cavity to the stomach.
Describe the submucosa of the esophagus.
- Contains mucus-secreting glands
- The mucus secreted is transported through a duct to be deposited in the lumen of the esophagus
- This mucus will lubricate the tract to allow food to pass through more easily
Describe the muscularis externa of the esophagus.
- typically consists of only smooth muscle, however, in the esophagus, this layer includes both smooth and skeletal muscle
- the upper 1/3 is only skeletal muscle, the middle 1/3 is mixed skeletal and smooth muscle fibers, and the lower 1/3 is entirely smooth muscle
Describe the serosa/adventitia of the esophagus.
The majority of esophagus is covered by adventitia, which is composed of loose connective tissue.
What are the regions of the stomach?
- Fundus
- Body
- Antrum
What is the greater Omentum?
A structure that hangs off of the greater curvature of the stomach. It is an apron-like structure that covers and protects the abdominal viscera.
Describe the mucosa of the stomach.
- folded into ridges and folds called rugae (non-permanent folds and allow the stomach to expand following ingestion of food or liquid)
- the epithelium is simple columnar, and inward folds extend down into the lamina propria to form gastric glands
- the epithelium secretes mucus, which helps protect the stomach from acids secreted by the gastric glands. these acids facilitate the chemical digestion of food.
Describe the submucosa of the stomach.
contains blood vessels, lymphatics, glands, and nerve plexuses, which supply the stomach tissue with oxygen and control contraction of the musculature
Describe the muscularis externa of the stomach.
- has three layers of smooth muscle arranged in different directions: an outer longitudinal, middle circular, and an inner oblique layer
Describe the serosa/adventitia of the stomach.
- the stomach is covered by serosa
Why does the stomach have three layers of muscle while the esophagus only has two?
The stomach needs to churn food during digestion, as well as push it toward the small intestine. These actions require more muscular power.
Compare and contrast the histological layers of the upper esophagus, lower esophagus, and stomach.
The major change in histology of the upper to lower esophagus is in the muscularis externa, which changes from skeletal (upper) to mixed smooth muscle (lower).
The stomach also has three layers compared to the esophagus, which only has two layers.
There are also differences in the mucosa, transitioning from stratified squamous in the esophagus to simple columnar in the stomach.
Explain the differences in the mucosa of the esophagus and stomach are observed.
The differences in mucosa exist due to the function of the esophagus and stomach. The esophageal epithelium allows for protection against friction of food passing from the oral cavity to the stomach. The stomach secretes acid, to chemically digest food, and secretes mucus that protects stomach lining from the secreted acid.
