Download Ch. 25 / 28 Anatomy of the Digestive System Notes

Anatomy & Physiology
Chapter 28:
Anatomy of the Digestive System
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Organization of the Digestive System

Organs of digestion (Figure 28-1)
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
Main organs of the digestive system
form the GI tract that extends through
the abdominopelvic cavity
Ingested food material passing
through the lumen of the GI tract is
outside the internal environment of
the body
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Organization of the Digestive System

Wall of the GI tract (Figure 28-2)
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Mucosa—innermost layer
Submucosa—contains numerous glands,
blood vessels, and parasympathetic
nerves
Muscularis—thick layer of muscle tissue
Serosa—outermost layer
Modifications of layers—structure of layers
varies in different regions throughout
length of GI tract (Table 28-1)
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Mouth

Structure of the oral cavity (buccal
cavity) (Figure 28-3)

Lips
 Covered externally by skin and
internally by mucous membrane
 Junction between skin and mucous
membrane is highly sensitive
 Line of contact between closed lips
forms the oral fissure
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Mouth

Structure of the oral cavity (cont)

Cheeks
 Lateral boundaries of the oral
cavity, continuous with the lips and
lined by mucous membrane
 Formed in large part by the
buccinator muscle covered by
adipose tissue
 Contain mucus-secreting glands
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Mouth

Structure of the oral cavity (cont)

Hard palate and soft palate
 Hard palate consists of portions of
four bones: two maxillae and two
palatines
 Soft palate forms the partition
between the mouth and
nasopharynx and is made of
muscle arranged in an arch
 Suspended from the midpoint of the
posterior border of the arch is the
uvula
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Mouth

Structure of the oral cavity (cont)
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Tongue—solid mass of skeletal muscle
covered by a mucous membrane; extremely
maneuverable
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Has three parts: root, tip, and body (Figure 284)
Papillae located on the dorsal and lateral
surfaces of the tongue (Figure 28-5)
Lingual frenulum anchors the tongue to the
floor of the mouth (Figure 28-6)
Intrinsic muscles important for speech and
mastication; extrinsic muscles important for
deglutition and speech (Figure 28-7)
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Mouth
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Salivary glands

Three main pairs of compound tubuloalveolar
glands (Figure 28-8)
Secrete approximately 1 liter of saliva each day
 Additional small buccal glands contribute less
than 5% of the total salivary volume but provide
for hygiene and comfort of oral tissues
Parotid glands—largest of the paired salivary glands;
produce watery saliva containing enzymes
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Submandibular glands—compound glands that
contain enzyme- and mucus-producing elements
Sublingual glands—smallest of the salivary glands;
produce a mucous type of saliva
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Mouth
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Teeth—organs of mastication
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Typical tooth (Figure 28-9)
 Crown—exposed portion of a tooth,
covered by enamel; ideally suited to
withstand abrasion during mastication
 Neck—narrow portion that joins the
crown to the root; surrounded by
gingivae
 Root—fits into the socket of the alveolar
process; suspended by a fibrous
periodontal membrane
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Mouth

Typical tooth (cont)
• Outer shell contains two additional
tissues: dentin and cementum
 Dentin—greatest portion of the tooth
shell; at the crown, covered by
enamel, and at the neck and root,
covered by cementum
 Pulp cavity—located in dentin,
contains connective tissue, blood,
and lymphatic vessels and sensory
nerves
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Mouth

Teeth—organs of mastication
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Types of teeth (Figure 28-10)
• Deciduous teeth—20 baby teeth,
which appear early in life
• Permanent teeth—32 teeth, which
replace the deciduous teeth
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Pharynx
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Tube through which a food bolus
passes when moved from the mouth
to the esophagus by the process of
deglutition
Air passes through all three divisions
of the pharynx; only terminal portion
involved in digestive system
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Esophagus
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Tube that extends from the pharynx
to the stomach; first segment of the
digestive tube (Figure 28-11)
Lined with stratified squamous
epithelium (Figure 28-12)
Each end encircled by muscular
sphincters
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Stomach
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Size and position of the stomach
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Size varies according to factors such as
gender and amount of distention
 When no food is in the stomach, it is
about the size of a large sausage
 In adults, its capacity ranges from 1.0
to 1.5 liters
Stomach location: upper part of the
abdominal cavity under the liver and
diaphragm
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Stomach
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Divisions of the stomach (Figure 28-13)
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Cardia—collarlike region at junction with
esophagus
Fundus—enlarged portion to the left and
above the opening of the esophagus into
the stomach
Body—central portion of the stomach
Pylorus—lower part of the stomach
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Stomach
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Curves of the stomach
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Lesser curvature—upper right curve of the
stomach
Greater curvature—lower left curve of the
stomach
Sphincter muscles—circular fibers arranged so
that there is an opening in the center when
relaxed and no opening when contracted
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Lower esophageal sphincter (LES), or cardiac
sphincter, controls the opening of the esophagus
into the stomach
Pyloric sphincter controls the outlet of the pyloric
portion of the stomach into the duodenum
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Stomach
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Stomach wall (Figure 28-14)
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Gastric mucosa
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Epithelial lining has rugae marked by gastric pits
(Figure 28-15)
Gastric glands—found below the level of the pits;
secrete most of the gastric juice
Chief cells—secretory cells found in the gastric
glands; secrete the enzymes of gastric juice
Parietal cells—secretory cells found in the gastric
glands; secrete hydrochloric acid; thought to
produce intrinsic factor needed for vitamin B12
absorption
Endocrine cells—secrete gastrin and ghrelin
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Stomach
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Stomach wall (cont)
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Gastric muscularis
 Thick layer of muscle with three
distinct sublayers of smooth
muscle tissue arranged in a
crisscrossing pattern
 This pattern allows the stomach to
contract strongly at many angles
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Stomach
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Functions of the stomach
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Reservoir for food until it is partially digested
and moved further along the GI tract
Secretes gastric juice to aid in digestion of food
Breaks food into small particles and mixes
them with gastric juice
Secretes intrinsic factor
Performs limited absorption
Produces gastrin and ghrelin
Helps protect the body from pathogenic
bacteria swallowed with food
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Small Intestine

Size and position of the small intestine
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Tube approximately 2.5 cm in diameter
and 6 m in length
Coiled loops fill most of the abdominal
cavity (Figure 28-16)
Divisions of the small intestine
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Duodenum—uppermost division;
approximately 25 cm long, shaped
roughly like the letter C
Jejunum—approximately 2.5 m long
Ileum—approximately 3.5 m long
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Small Intestine

Wall of the small intestine (Figure 28-17)
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Intestinal lining has plicae with villi
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Villi—important modifications of the mucosal layer
Each villus contains an arteriole, venule, and
lacteal vessel
 Covered by a brush border made up of 1700
ultrafine microvilli per cell
 Villi and microvilli increase the surface area
of the small intestine hundreds of times
Crypts—located between villi; contain stem cells
from which other cell types are produced and then
migrate upward to cover the villi, where they
eventually slough off (Figure 28-18)


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Large Intestine

Size of the large intestine
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Average diameter, 6 cm
Length, approximately 1.5 to 1.8 m
Divisions of the large intestine
(Figure 28-19)

Cecum—first 5 to 8 cm of the large
intestine; blind pouch located in the
lower right quadrant of the abdomen
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Large Intestine
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Divisions of the large intestine (cont)
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Colon
Ascending colon—vertical position on the right
side of the abdomen; the ileocecal valve prevents
material from passing from the large intestine into
the ileum
 Transverse colon—passes horizontally across
the abdomen, above the small intestine; extends
from the hepatic flexure to the splenic flexure
 Descending colon—vertical position on left side
of the abdomen
 Sigmoid colon joins the descending colon to the
rectum

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Large Intestine
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Divisions of the large intestine (cont)
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Rectum
 Last 7 or 8 inches of the intestinal tube
 Terminal inch is the anal canal with the
opening called the anus (Figure 28-20)
Wall of the large intestine (Figure 28-21)


Intestinal mucous glands produce
lubricating mucus that coats feces as
they are formed
Uneven distribution of fibers in the
muscle coat
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Veriform Appendix
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Accessory organ of digestive
system
8 to 10 cm in length;
communicates with the cecum
Serves as reservoir for beneficial
gut bacteria
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Peritoneum
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Large, continuous sheet of serous
membrane (Figure 28-22)
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Many organs are covered with visceral
peritoneum; parietal peritoneum then
lines the wall of the abdominopelvic
cavity
Extraperitoneal space is outside the
parietal layer of the peritoneum;
retroperitoneal identifies the
extraperitoneal space along the posterior
and bottom of the abdominopelvic cavity.
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Peritoneum
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Mesentery—projection of the parietal
peritoneum; allows free movement of
each coil of the intestine and helps
prevent strangulation of the long tube
(Figure 28-23)
Transverse mesocolon—extension of
the peritoneum that supports the
transverse colon
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Liver

Location and size of the liver
(Figure 28-24)
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Largest gland in the body, weighs
approximately 1.5 kg
Lies under the diaphragm;
occupies most of the right
hypochondrium and part of the
epigastrium
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Liver
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Liver lobes and lobules—two lobes
separated by the falciform ligament
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Left lobe—forms about one sixth of the
liver
Right lobe—forms about five sixths of the
liver; divides into right lobe proper,
caudate lobe, and quadrate lobe
Hepatic lobules—anatomical units of the
liver; a small branch of the hepatic vein
extends through the center of each lobule
(Figures 28-25 and 28-26)
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Liver
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Bile ducts (Figure 28-27)
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Small bile ducts form right and left
hepatic ducts
Right and left hepatic ducts
immediately join to form one hepatic
duct
Hepatic duct merges with the cystic
duct to form the common bile duct,
which opens into the duodenum
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Liver

Functions of the liver
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Detoxification by liver cells—ingested toxic substances and
toxic substances formed in the intestines may be changed to
nontoxic substances
Bile secretion by liver—bile salts are formed in the liver from
cholesterol and are the most essential part of bile; liver cells
secrete approximately 1 pint of bile per day
Liver metabolism—carries out numerous important steps in
metabolizing proteins, fats, and carbohydrates

Storage of substances such as iron and some vitamins

Production of important plasma proteins
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Gallbladder

Size and location of the gallbladder
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
Pear-shaped sac 7 to 10 cm long and 3
cm wide at its broadest point
Lies on the undersurface of the liver
(Figure 28-27)
Structure of the gallbladder


Serous, muscular, and mucous layers
compose the gallbladder wall
The mucosal lining has rugae that
expand to allow storage of bile; holds 30
to 50 ml of bile
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Gallbladder
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Functions of the gallbladder
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Storage of bile
Concentration of bile fivefold to tenfold
Ejection of the concentrated bile into
the duodenum
Gallstones—often made of
cholesterol; can form when bile
becomes concentrated (Figure 28-28)
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Pancreas

Size and location of the pancreas
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
Grayish pink–colored gland; 12 to 15
cm long; weighs approximately 60
grams
Runs from the duodenum, behind the
stomach, to the spleen
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Pancreas

Structure of the pancreas (Figure 28-29)—
composed of endocrine and exocrine glandular
tissue
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
Exocrine portion makes up the majority of the
pancreas; has a compound acinar arrangement;
tiny ducts unite to form the main pancreatic duct,
which empties into the duodenum
Endocrine portion—embedded between exocrine
units; called pancreatic islets; constitute only 2%
of the total mass of the pancreas; made up of
alpha cells and beta cells; pass secretions into
capillaries
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Pancreas
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Functions of the pancreas
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Acinar units secrete digestive
enzymes
Beta cells secrete insulin
Alpha cells secrete glucagon
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Cycle of Life: Digestive System

Changes in digestive function and structure
are age related

Result in diseases or pathological conditions

May occur in any segment of the intestinal tract


Changes involve accessory organs: teeth,
salivary glands, liver, gallbladder, and pancreas
Infants have immature intestinal mucosa

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Intact proteins can pass through epithelial cells
lining the tract and trigger an allergic response
Lactose intolerance affects infants who lack the
enzyme lactase
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Cycle of Life: Digestive System
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

Mumps common in children; appendicitis
more common in adolescents and then
incidence decreases with advancing age
Ulcers and gallbladder disease common
in middle age
Decreased digestive fluids, slowing of
peristalsis, and reduced physical activity
lead to constipation and diverticulosis in
the elderly
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