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Chapter 24
5 – Deglutition & The Stomach
Deglutition
• A bolus is a soft, rounded mass of food that is
formed in the mouth when food is mixed
with saliva.
Deglutition
– Once the bolus is swallowed, it passes from the
mouth into the pharynx.
Deglutition
• The pharynx is a funnel-shaped tube that
starts at the back of the mouth and runs down
the neck where it opens into the esophagus
posteriorly and the larynx anteriorly.
Deglutition
• The esophagus is a hollow muscular tube that
connects the pharynx to the stomach.
Deglutition
• Deglutition (swallowing) is the movement of
food from the mouth into the stomach.
Deglutition
• Deglutition occurs in three stages:
1. The voluntary stage
2. The pharyngeal stage
3. The esophageal stage
Deglutition
1. The voluntary stage starts when the bolus is
forced to the back of the oral cavity and into
the pharynx by the movement of the
tongue.
Deglutition
2. The pharyngeal stage begins when the bolus
moves into the pharynx and the brain stem
sends impulses to the epiglottis to close the
opening of the larynx which prevents the
bolus from entering the trachea.
Deglutition
3. The esophageal stage begins once the bolus
enters the esophagus; during this phase
peristalsis pushes the bolus into the
stomach.
Deglutition
• Peristalsis is a progression of successive
muscular contractions that occurs in the
muscularis of the GI tract.
The Stomach
• The stomach is a J-shaped enlargement of the
GI tract that connects the esophagus to the
duodenum.
The Stomach
• The stomach has four main regions:
1. The cardia
2. The fundus
3. The body
4. The pylorus
The Stomach
1. The carida surrounds the superior opening of
the stomach.
The Stomach
2. The fundus is the rounded portion superior
to and to the left of the cardia.
The Stomach
3. The body is the large central portion of the
stomach inferior to the fundus.
The Stomach
4. The pylorus is the region of the stomach that
connects the duodenum; it communicates
with the duodenum via a sphincter called
the pyloric sphincter.
The Stomach
• **The stomach wall is composed of the same
four basic layers of the GI tract, with certain
modifications.
The Stomach
• **Recall – the four layers of the GI tract are:
the mucosa, the submucosa, the muscularis,
and the serosa.
The Stomach
• **The mucosa of the stomach contains
secretory cells called ‘gastric glands’ that
empty their secretions into narrow channels
called gastric pits.
The Stomach
• Gastric glands are glands in the mucosa of the
stomach; the four types of cells are chief cells,
parietal cells, mucous neck cells and G cells.
The Stomach
1. Chief cells secrete pepsinogen & gastric
lipase
2. Pareital cells secrete hydrochloric acid (HCl)
3. Mucous neck cells secrete mucus
4. G cells secrete gastrin
The Stomach
• **The digestion that occurs in the stomach is
both mechanical and chemical.
The Stomach
1. Mechanical digestion in the stomach
consists of peristaltic movements called
‘mixing waves’ that intensify as food reaches
the pylorus.
The Stomach
• Mixing waves macerate food, mix it with
secretions of the gastric glands, and reduce it
to chyme.
The Stomach
• Chyme is the semifluid mixture of partly
digested food and digestive secretions found
in the stomach and small intestine during the
digestion of a meal.
The Stomach
• **As food reaches the pylorus, each mixing
waves periodically forces about 3 mL of chyme
into the duodenum through the pyloric
sphincter.
The Stomach
– Most of the chyme is forced back into the
stomach where mixing continues; the next wave
pushes the chyme forward again and forces a
little more into the duodenum.
The Stomach
2. Chemical digestion in the stomach consists
of the conversion of proteins into peptides by
pepsin, and triglycerides into fatty acids and
glycerol by the enzymes lingual lipase &
gastric lipase.
The Stomach
• **Pepsin, lingual lipase & gastric lipase are all
activated in extremely acidic environments.
The Stomach
• **Recall – the acid (HCl) is secreted by the
stomach’s parietal cells; it creates a very acidic
environment (pH 2) in the stomach.
The Stomach
• **Recall – ‘pepsinogen’ is secreted by the
stomach’s chief cells.
The Stomach
• **Pepsinogen is converted into active ‘pepsin’
when it comes in contact with HCl.
The Stomach
• The stomach wall is impermeable to most
substances; however, some water,
electrolytes, certain drugs (especially aspirin),
and alcohol can be absorbed through the
stomach lining.
The Stomach
• From the stomach, chyme passes into the
small intestine; chemical digestion in the small
intestine is not autonomous, it depends on
activities of accessory digestive organs.
Homework
• Finish handout:
– “Deglutition & The Stomach”
• Study for mini-quiz