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Chapter 14 – Part 2
The Digestive System
Stomach Anatomy
 Located on the left
side of the
abdominal cavity
 C-shaped
 Nearly hidden by
the liver and
diaphragm
Stomach Anatomy
 Regions of the
stomach
 Cardiac region –
near the heart
 Fundus – expanded
part lateral to the
cardiac region
 Body - midportion
 Pylorus – funnelshaped terminal
end
Stomach Anatomy
 Food enters the
stomach at the
cardioesophageal
sphincter
 Food empties into
the small intestine
at the pyloric
sphincter
Stomach Anatomy
 The stomach is about 10 inches long
 Its diameter depends on how much food
it contains
 When it is full it can hold about 1
gallon of food
 When it is empty it collapses inward
on itself
Stomach Anatomy
 Rugae – internal folds
of the mucosa (seen
especially when the
stomach is empty)
 External regions
 Lesser curvature – the convex lateral
surface of the stomach (smaller curve)
 Greater curvature – the concave medial
surface of the stomach (larger curve)
Stomach Anatomy
 There are two layers of peritoneum that
are attached to the stomach:
 Lesser omentum – attaches the liver to
the lesser curvature
 Greater omentum – attaches the greater
curvature to the posterior body wall
 Drapes downward and covers the
abdominal organs like a lacy apron
 Contains fat which helps to insulate,
cushion, and protect abdominal organs
Greater and Lesser Omentum
Peritonitis
 Peritonitis – occurs when the
peritoneum is infected
 The peritoneal membranes tend to
stick together around the infection
site
 Helps to seal off and localize many
intraperitoneal infections
 Provides time for macrophages to
mount an attack
Stomach Anatomy
Stomach Functions
1. Acts as a storage
for food
tank
2. Site of food breakdown
3. Chemical breakdown of protein begins
4. After food has been processed in the
stomach, it delivers chyme (processed
food) to the small intestine
Structure of the Stomach Mucosae
 Besides the usual longitudinal and
circular muscle layers, the stomach
contains a third obliquely arranged layer
in the muscularis externa.
 Does more than just move food along
the tract
 Allows it to churn, mix and pummel the
food, physically breaking it down to
smaller fragments
Stomach Anatomy
Specialized Mucosa of the Stomach
 The mucosae of the
stomach is a simple
columnar epithelium
that produces large
amounts of mucus.
 It dotted with deep
gastric pits (formed
by folded mucosa)
 Glands and specialized
cells are in the gastric
gland region
Specialized Mucosa of the Stomach
Mucous neck cells – produce a sticky
alkaline mucus
 Clings to the stomach mucosa and protects
the stomach wall itself from being damaged
by the acid and digested by the enzymes
Gastric glands – secrete gastric juice
Specialized Mucosa of the Stomach
Chief cells – produce protein-digesting
enzymes (pepsinogens)
Parietal cells – produce hydrochloric
acid, which makes the stomach acidic
and activates the enzymes
Endocrine cells – produce gastrin
(important for digestion)
Structure of the Stomach Mucosa
Small Intestine
 The body’s major digestive
organ
 Site of nutrient absorption
into the blood
 Muscular tube extending from the pyloric
sphincter to the ileocecal valve
 Longest section of the alimentary canal (613 feet in a living person)
 Is encircled and framed by the large
intestine
Small Intestine: Three Subdivisions
1. Duodenum
 Attached to the stomach
 Curves around the head
of the pancreas
 About 10 inches long
2. Jejunum
 Extends from the duodenum to the ileum
 About 8 feet long
3. Ileum
 Terminal part of the small intestines
 About 12 feet long
Chemical Digestion in the Small
Intestine
 The small intestine is
able to process only
a small amount of
food at one time
 The pyloric sphincter
(literally, “gatekeeper”):
 Controls food movement into the small
intestine from the stomach
 Prevents the small intestine from being
overwhelmed
Chemical Digestion in the Small
Intestine
 Enzymes complete the
chemical breakdown of
food in the small intestine
 Source of enzymes that are mixed with
chyme
Produced by the intestinal cells
Produced by the pancreas and ducted
into the duodenum of the small
intestine via the pancreatic duct
Chemical Digestion in the Small
Intestine
 Bile enters the duodenum from the gall
bladder via the bile duct
 Bile is formed by the liver
 Bile helps to break down fats
Chemical Digestion in the Small
Intestine
Figure 14.6
Main Function of the Small Intestine
 Nearly all food absorption occurs in the
small intestine
 Its wall has three structures that increase
the absorptive surface tremondously
1. Microvilli
2. Villi
3. Circular Folds
 Well suited for absorption
 These structural modifications decrease in
number toward the end of the small intestine
Villi of the Small Intestine
 Villi - Fingerlike
structures of the
mucosa
 Give the small
intestine more
surface area
 Gives it a velvety
appearance
Microvilli of the Small Intestine
 Microvilli - small
projections of the plasma
membrane
 Gives the cell surface a
fuzzy appearance
 Sometimes referred to as
brush border
 Found on absorptive cells
Microvilli and Villi of the Small Intestine
Structures Involved in Absorption of
Nutrients
 Digested foodstuffs
are absorbed through
the villus of mucosa
cells via:
1. Rich capillary bed
2. A modified
(specialized)
lymphatic capillary
called a lacteal
Folds of the Small Intestine
 Circular folds, called
plicae circulares,
are deep folds of
both the mucosa
and submucosa
layers
 Do not disappear
when filled with food
(unlike the rugae)
Folds of the Small Intestine
 The submucosa has
Peyer’s patches
(collections of lymphatic
tissue)
 More are found towards
the end of the small intestine
 The undigested food residue in the
intestine contains huge numbers of
bacteria, which must be prevented from
entering the bloodstream