Digestive One: Salivary Glands and Esophagus (Dog)

Parotid gland

A major salivary gland located around the base of the ear in dogs.

Mandibular gland

A salivary gland located near the mandible, closely associated with mandibular lymph nodes.

Sublingual gland

A salivary gland located under the tongue.

Zygomatic gland

A salivary gland located deep to the zygomatic arch.

Parotid gland duct

Runs across the masseter muscle and opens into the oral cavity just above the fourth upper premolar.

Sublingual caruncles

Raised areas on either side of the midline under the tongue where the mandibular and sublingual glands' common duct exits.

Saliva release

Driven by parasympathetic activity, especially during rest, relaxation, and digestion ('rest-and-digest' phase).

Primary functions of saliva

Lubrication for bolus formation, swallowing, taste enhancement, and enzymatic digestion in some species.

Saliva composition

Predominantly water, proteins, glycoproteins (for viscosity), immunoglobulins (IgA), and electrolytes (e.g., bicarbonate).

Amylase

A salivary enzyme that digests carbohydrates; its presence varies by species.

Lipase

A salivary enzyme that digests fats; notable as a temporary enzyme in newborn mammals for milk fat digestion.

IgA

Immunoglobulin A; an antibody in saliva providing nonspecific oral defense against microbes.

Bicarbonate (NaHCO₃) in saliva

Helps neutralize acids, particularly important in species with significant gastric/ruminal acidity.

Ramula

A blister-like, fluid-filled lesion beneath the tongue caused by a clog at the sublingual caruncle.

Salivary Mucocele (sialomucocele)

A more posterior/ductal obstruction where saliva leaks into subcutaneous spaces, forming a fluctuating mass, often in the neck area.

Treatment for salivary mucocele

Typically requires surgical removal of the affected salivary gland due to high recurrence rates if only the duct is opened.

Pharynx

A pathway for food after bolus formation, subdivided into nasopharynx, oropharynx, and laryngopharynx.

Esophagus

A muscular tube that transports the bolus from the pharynx to the stomach.

Four tunics (layers) of the esophagus

Mucosa (innermost), submucosa, muscularis (longitudinal and circular), and serosa (outermost).

Muscularis layers

Composed of longitudinal and circular muscle layers that coordinate to produce peristaltic movement.

Peristalsis

Coordinated contractions of longitudinal and circular muscle layers that advance the bolus toward the stomach.

Lower Esophageal Sphincter (LES)

A muscular narrowing at the distal esophagus that prevents backflow from the stomach into the esophagus.

Esophageal hiatus

The opening in the diaphragm through which the esophagus passes.

Hiatal hernia

Herniation of a portion of the esophagus (and potentially stomach) through the diaphragmatic hiatus.

Megaesophagus

A condition where the esophagus dilates and loses peristaltic function, increasing the risk of regurgitation and aspiration pneumonia.

Diagnostic approach for megaesophagus

Barium swallow/contrast radiography to show the dilated esophagus with poor contrast transport.

Management for megaesophagus

Elevated feeding to use gravity for food movement, and sometimes prokinetic medications.