Always in motion is the future.

GE 345: Week 5

Mouth & Esophagus

Chewing and Swallowing

The mechanical process of digestion begins with mastication of the bolus, increasing surface area exposed to digestive enzymes, which only act on the surface of food particles. Chewing is a reflexive process, stimulated by the pressure of the bolus in the mouth.

Deglutition (swallowing) has two stages:

Voluntary: tongue presses up & back against palate, squeezing/rolling bolus posteriorly into pharynx.
Pharyngeal: movement of bolus into back of mouth triggers involuntary series of pharyngeal contractions, closing the trachea, temporarily halting respiration, opening the esophagus. Peristaltic waves move bolus into the upper esophagus.

Salivary Secretions

Salivary glands contain two major protein secretion types:

serous secretions containing ptyalin, an alpha-amylase, a starch-digesting enzyme secreted by parotid, submandibular, and sublingual glands begin starch hydrolyzing process.
mucus secretions containing mucin secreted by submandibular, sublingual and buccal glands contain mucin to lubricate and protect surfaces.

Under basal conditions, except sleep, almost all saliva secreted is mucus. Functions of saliva include:

help was away pathogenic bacteria which can destroy tissue and cause cavities.
ions and proteolytic enzymes in saliva can destroy bacteria and digest food particles, thereby removing metabolic support for bacteria.
protein atibodies in saliva can destroy oral bacteria.

Salivatory nuclei in the brain stem control salivary secretion, and are activated by:

taste and tactile stimuli from tongue and mouth.
signals from higher brain centers which are in turn influenced by how much a particular food is liked or disliked.
presence of irritating foods or nausea. Swallowed saliva can dilute or neutralize certain irritants.

The esophagus

In the esophagus, primary peristalsis, a continuation of the wave initiated in the pharynx, moves the bolus from pharynx to stomach in 8-10s. If primary wave doesn't move all the food, secondary waves are initiated. A relaxation wave precedes the peristaltic wave, which relaxes the gastroesophageal sphincter (which normally is tonically constricted to prevent reflux of acidic stomach contents into the esophagus), and prepares the stomach to receive the bolus.

Esophageal secretions are mainly lubricating mucus. Toward the gastric end, the mucus is more complex, protecting that section from gastric reflux.