ESOPHAGUS

Function: muscular tube that delivers food and liquid from oropharynx to the stomach.

MUCOSA

Function:

• barrier - separates the lumen of the digestive tract, which is continuous with the environment, from the body of the organism.
• secretory - synthesizes and secretes mucus.

Composition:

• stratified squamous nonkeratinized epithelium (in humans) or stratified squamous keratinizing epithelium (in many animals).
• lamina propria - loose connective tissue, blood capillaries and lymphatic capillaries, nerves, diffuse lymphatic tissue, lymphatic nodules, cardiac glands.
• muscularis mucosae - longitudinally organized smooth muscle layer.

SUBMUCOSA

Function: forms the number of longitudinal folds. As bolus of food passes down the esophagus, the folds flatten out, resulting a localized dilation of the lumen.

Composition: moderately dense irregular connective tissue, blood vessels, lymphatic vessels, nerve network, esophageal glands proper.

MUSCULARIS EXTERNA

Function: propels the contents by shortening the tube.

Composition: the upper 1/3 - striated muscle that circular layer is thickened to form pharyngoesophageal sphincter, the middle third - striated muscle and smooth muscle, the distal third - smooth muscle.

ADVENTITIA

Composition: in thoracic cavity: loose connective tissue, in abdominal cavity: serosa - loose connective tissue covered by simple squamous epithelium - mesothelium, white adipose tissue.

GLANDS

Function: mucus secretion.

• Esophageal glands proper - small compound tubuloacinar glands.

• Esophageal cardiac glands - simple branched tubular glands