Physiology of the Gastrointestinal System I: Ingestion and Propulsion

The physiology of the gastrointestinal system starts with ingestion as food enters the mouth.

Mechanical digestion begins with mastication, involving both upper and lower jaws.

The salivary glands, including the parotid, submandibular, and sublingual glands, release saliva-containing enzymes like salivary amylase.

These enzymes start carbohydrate breakdown and moisten the food to form a bolus for easier swallowing.

During deglutition, the tongue pushes the bolus toward the pharynx, triggering an involuntary reflex that closes off the nasopharynx and trachea, directing the bolus into the esophagus.

Receptors in the oropharynx activate a swallowing reflex, raising the soft palate to seal the nasopharynx and blocking the trachea with the epiglottis to prevent food from entering the respiratory tract.

Once in the esophagus, peristalsis, which involves coordinated rhythmic contractions of the esophageal muscles, moves the bolus downward to the stomach.

The upper esophageal sphincter allows food to enter the esophagus, while the lower sphincter regulates entry into the stomach and prevents reflux.