The Stomach

The Stomach

• J-shaped enlargement of the GI tract

• Most distensible part of the GI tract

• Connects esophagus to the duodenum

• Directly inferior to the diaphragm in the umbilical, and
left hypochondriac regions of the abdomen

Regions of the Stomach

• Serve as a mixing chamber and holding reservoir

• Digestion of starch continues

• Digestion of proteins and triglycerides begins

• Certain substances are absorbed

Anatomy of

• The Cardia

– Surrounds the superior opening of the stomach

• The Fundus

– Rounded portion superior to, left of the cardia

• The Body

– Inferior to the fundus, large central portion

• The Pylorus

– Region of the stomach that connects to the duodenum

– Pyloric antrum – Connects to the body of the stomach

– Pyloric canal – Leads into the duodenum


– When the stomach is empty, the mucosa lies in large folds

– can be seen with the unaided eye

• The Pyloric

– Pylorus communicates with the duodenum via a smooth muscle
sphincter called the pyloric sphincter

• Lesser curvature

– The concave medial border

• Greater curvature

– The convex lateral border

Overview of

The stomach wall is composed of the same basic layers as the
rest of the GI tract, with certain modifications

of the Stomach


• Layer of simple columnar epithelial cells called surface
mucous cells

• Lamina propria (areolar connective tissue)

• Muscularis mucosae (smooth muscle)

• Epithelial cells extend down into the lamina propria &
form gastric glands

• Several gastric glands open into the bottom of narrow
channels called gastric pits

• The gastric glands contain three types of exocrine gland

• Gastric glands include a type of enteroendocrine cell – G

of the Stomach


• Composed of areolar connective tissue


• Three layers of smooth muscle

• Outer longitudinal layer

• Middle circular layer

• Inner oblique layer


• Composed of simple squamous epithelium (mesothelium) and
areolar connective tissue

of Stomach

• Mechanical digestion consists of mixing waves

• Chemical digestion – conversion of proteins into peptides
by pepsin

• The stomach wall is impermeable to most substances

• Among the substances the stomach can absorb are water,
certain ions, drugs, and alcohol

Digestion in the Stomach

• Gentle, rippling, peristaltic movements called mixing
waves pass over the stomach every 15 to 25 seconds

• These waves macerate food, mix it with secretions of the
gastric glands – chyme

• Few mixing waves are observed in the fundus

• Primarily has a storage function

• Intensify as
they reach the pylorus

• Gastric emptying –
Each mixing wave periodically forces about 3 mL of chyme into the duodenum
through the pyloric sphincter

Digestion in Stomach

• Churning action
mixes chyme with acidic gastric juice

• Enzymatic digestion of proteins also begins in the stomach

• Acidic fluid of
the stomach kills many microbes in food

• HCl

– Partially denatures (unfolds) proteins in food

– Stimulates the secretion of hormones that promote the flow of
bile and pancreatic juice

Digestion Process


• The only proteolytic enzyme in the stomach

• Secreted in an inactive form called pepsinogen; activated
by H

• Pepsin breaks down proteins into smaller peptide fragments

• Pepsin is most effective in the very acidic environment of
the stomach (pH 2)

• Becomes inactive at a higher pH

Alkaline Mucus

• Secreted by surface mucous cells and mucous neck cells

• Protect the stomach epithelial cells from gastric juices
(1–3 mm thick layer of alkaline mucus)

• Gastric lipase

– Splits the short-chain triglycerides in fat molecules into
fatty acids and monoglycerides

– Has a limited role in the adult stomach