**2. Structure of esophagus**

Esophagus consists of four histologic layers: mucosa, submucosa, muscularis propia, and adventitia.

**Figure 1.** Anatomy of larynx (with permission of Turkish Surgery Association).

**Figure 2.** Length of esophageal parts.

#### **2.1. Mucosa**

Nonkeratinized stratified squamous epithelium covers all esophageal lumen. Lamina propia and lamina muscularis mucosa are located under this epithelium. Lamina propia consists mostly of loose connective tissue and lamina muscularis mucosa consists of some smooth muscle tissue and elastic fibers. Nonkeratinized stratified squamous epithelium of mucosa transforms simple columnar epithelium in cardia of stomach, occurring at a point called "Z line," an irregular zigzag line. On endoscopy, esophageal mucosa is paler than mucosa of stomach.

#### **2.2. Submucosa**

This layer consists of elastic and collagen fibers that form a dense, irregular connective tissue. This layer consists of veins, lymphatics, and meissner plexus.

#### **2.3. Muscularis propia**

Both longitudinal and circular muscles form tube-like esophagus: longitudinal muscle fibers are located superficially and the circular muscle fibers are located deeply. Longitudinal fibers begin from posterior face of cricoid cartilage and form a triangle named as "Lamier triangle," which is limited by longitudinal muscle fibers laterally and cricopharyngeus muscle superiorly. Another triangle, called "Killian triangle," is found in this area, and borders of this triangle are formed by inferior constrictor muscle of pharynx and cricopharyngeus muscle. These weaker areas are important for the formation of Zencker's diverticula. Longitudinal muscle fibers are gathered laterally in upper portion of esophagus, but these fibers expand and surround all surfaces at lower sides, becoming strongest in lower third part of esophagus. Circular muscle fibers are located under longitudinal muscle, and the circular muscle is thinner than longitudinal muscle. Circular muscles are not actually circular at all parts of esophagus; these fibers are more elliptic in upper third part and become more circular at lower third part of esophagus. Circular muscle fibers do not make a regular formation, but run in an irregular pattern making a shutter-like system. Spontaneous perforation of esophagus usually occurs in last 2 cm, and this perforation consists of entire esophageal wall, causing mediastinitis because of gastric acid leakage. Upper part of esophagus consists of striated muscle and the lower part consists of smooth muscle fibers. Transition zone differs in all humans, but mostly upper quarter consists only of striated muscle fibers; second quarter consists of both striated and smooth muscle fibers; and lower half consists of only smooth muscle fibers (Aurbach plexus is in this layer).

#### **2.4. Adventitia**

**Figure 2.** Length of esophageal parts.

**Figure 1.** Anatomy of larynx (with permission of Turkish Surgery Association).

4 Esophageal Abnormalities

This layer surrounds most of the esophagus and consists of loose connective tissue. Because no serosa is found on esophagus, infections, and tumors can spread easily [5, 6].
