b. Pharynx. The pharynx contributes to the digestive process by deglutition.
The wall of the pharynx contains three pharyngeal constrictor muscles. By wave-like
contractions, these muscles force the food mass (the bolus) down into the beginning of
c. Esophagus. Two processes contribute to digestion in the esophagus:
mechanical digestion and peristalsis. The functions of the esophagus are to secrete
mucus and transport food to the stomach. The process of deglutition continues as the
bolus continues on its way to the stomach. The involuntary muscular movements of
peristalsis which are wave-like movements squeeze food downward; through the
esophagus. This is the process of esophageal peristalsis:
(1) The circular muscles just above the bolus contract causing the
esophagus to become narrower thus pushing the bolus down the esophagus.
(2) The section of the esophagus just below the bolus adjust to make the
esophagus under the bolus widen to accept this food mass.
(3) These muscles continue in waves to contract continually pushing the
food mass toward the stomach.
(4) At the same time, glands in the esophagus secrete mucus which also
helps the food mass move through the esophagus.
Solid or semisolid food usually moves from the mouth to the stomach in from
four to eight seconds. Very soft foods and liquids pass from the mouth to the
stomach in about one second.
d. Stomach. Both mechanical digestion and chemical digestion take place in
(1) Mechanical digestion. The food mass enters the stomach, and several
minutes later mixing waves pass over the stomach. These are gentle, rippling peristaltic
movements which pass over the stomach every 15 to 25 seconds when there is food in
the stomach. The movement of these waves mixes the food with the secretions of the
gastric glands, softening the food mass, and reducing it to a thin liquid called chyme
(pronounced kim). The fundus portion of the stomach is mainly a storage area, and few
mixing waves take place there. Foods may be stored is the fundus for an hour or more
without becoming mixed with gastric juice. During this storage time, salivary digestion
continues. The food progresses through the stomach from the fundus to the body
where the mixing waves become stronger and even stronger as the food reaches the
pylorus. At the pylorus, each mixing wave forces a small amount of the stomach
contents into the duodenum. Most of the food is forced back into the body of the