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Module 1: Módulo 3: Introdução ao sistema digestivo humano

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When the food has been adequately broken down (increased surface area),
wetted thoroughly, and tested (tasted), it is ready to be swallowed.
a. The bolus is moved posteriorly out of the mouth (oral cavity) into the pharynx
and then down through the esophagus to the stomach.
b. The pharynx is common to both the digestive and respiratory systems.
Therefore, as the bolus passes through the pharynx, both the upper and lower air
passageways must be protected. Otherwise, food particles might enter the
passageways.

Step 1 Movement out of the oral Cavity
a. Initial Movement of the Bolus. There are intrinsic muscles in the tongue.
Through their action, the tongue arches upward and presses against the hard palate,
the roof of the mouth. This initiates the posterior movement of the bolus.
b. Action of the Hyoid Complex. The muscles of the hyoid bone pull the hyoid
bone upward and force the tongue upward into the oral cavity. This closes up the front
part of the oral cavity and forces the bolus further to the rear.
c. Action of the Soft Palate. As the bolus approaches the pharynx, the soft
palate is raised. Thus, the soft palate serves as a trap door to close the upper air
passageway. By tensing to resist the pressure from the bolus of food, the soft palate
ensures the continued backward movement of the bolus into the pharynx.

Step 2 Movement through the Pharynx
a. Pharyngeal Constrictor Muscles. The wall of the pharynx contains three
pharyngeal constrictor muscles. By wavelike contractions, these muscles force the
bolus down into the beginning of the esophagus.
b. Action of the Epiglottis. As the hyoid bone's muscles raise the tongue up
into the oral cavity, they also raise the larynx. The larynx is raised because it is
attached to the inferior margin of the hyoid bone. As the larynx is raised, its epiglottis
automatically turns down over the opening of the larynx. Thus, food is prevented from
entering the lower-air passage-way.

Step 3 Movement through the esophagus
The esophagus is a tube with muscular walls. It extends from the pharynx
above, through the neck and thorax, to the stomach in the abdomen. Wavelike
contractions (peristalsis) move the bolus through the esophagus to the stomach.