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Chapter 23
Digestive System
Overview of the Digestive
System
A. Role of the digestive system
1. Preparing food for absorption
2. Process of altering the chemical and
physical components of food so that
it can be absorbed and used by
body cells
Overview of the Digestive
System
B.
Organization of the
digestive system
1. Organs of
Digestive system
a. Segments of the
Gastrointestinal
track (GI)
1)
2)
3)
Mouth
Oropharynx
Esophagus
4)
5)
6)
7)
8)
Stomach
Small Intestine
Large Intestine
Rectum
Anal Canal
Figure 23.2 Gastrointestinal tract activities.
Ingestion
Mechanical
breakdown
• Chewing (mouth)
• Churning (stomach)
• Segmentation
(small intestine)
Digestion
Food
Pharynx
Esophagus
Propulsion
• Swallowing
(oropharynx)
• Peristalsis
(esophagus,
stomach,
small intestine,
large intestine)
Stomach
Absorption
Lymph
vessel
Small
intestine
Large
intestine
Blood
vessel
Mainly H2O
Feces
Defecation
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Anus
Overview of the Digestive
System
b. Accessory Organs
1) Salivary glands
2) Tongue
3) Teeth
4) Liver
5) Gallbladder
6) Pancreas
7) Vermiform appendix
Overview of the Digestive
System
2.
Wall of the GI track
a. The GI track is essentially a tube with
walls fashioned of four layers of tissue.
1) Mucosa – inner most layer
2) Submucosa – thicker than muscosa
3) Muscularis – wraps around the
submuscosa
4) Serosa – Outermost layer
Figure 23.6 Basic structure of the alimentary canal.
Intrinsic nerve plexuses
• Myenteric nerve plexus
• Submucosal nerve plexus
Glands in
submucosa
Mucosa
• Epithelium
• Lamina propria
• Muscularis
mucosae
Submucosa
Muscularis externa
• Longitudinal muscle
• Circular muscle
Mesentery
Nerve
Artery
Gland in mucosa
Vein
Duct of gland outside
Lymphatic vessel
alimentary canal
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Serosa
• Epithelium
(mesothelium)
• Connective tissue
Lumen
Mucosa-associated
lymphoid tissue
Overview of the Digestive
System
b. Modifications of layers
1) Variations in the epithelial layer
2) Upper esophagus have protection
from abrasion
3) Small intestine has a muscosal layer
which has microvilli to enhance
absorption
Mouth
A.
Structure of the Oral
Cavity
1.
Lips
2.
Cheeks
3.
Hard Palates –
consists of
portions of four
bones
4.
a.
Two maxillae
b.
Two palatines
Soft Palates
Figure 23.7a Anatomy of the oral cavity (mouth).
Soft
palate
Palatoglossal
arch
Uvula
Hard
palate
Oral cavity
Palatine
tonsil
Tongue
Oropharynx
Lingual tonsil
Epiglottis
Hyoid bone
Laryngopharynx
Esophagus
Trachea
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Sagittal section of the oral cavity and pharynx
Figure 23.7b Anatomy of the oral cavity (mouth).
Upper lip
Gingivae
(gums)
Palatine
raphe
Hard
palate
Soft
palate
Uvula
Palatine
tonsil
Superior
labial
frenulum
Palatoglossal
arch
Palatopharyngeal
arch
Posterior wall
of oropharynx
Tongue
Sublingual
fold with
openings of
sublingual
ducts
Lingual frenulum
Opening of
Submandibular
duct
Gingivae (gums)
Oral vestibule
Lower lip
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Anterior view
Inferior labial
frenulum
Mouth
4.
Tongue
a.
Skeletal muscle
covered by a
mucous
membrane
b.
Mastication –
chewing
c.
Deglutition –
swallowing
d.
Papillae – Taste
buds
Figure 23.8 Dorsal surface of the tongue, and the tonsils.
Epiglottis
Palatopharyngeal
arch
Palatine tonsil
Lingual tonsil
Palatoglossal
arch
Terminal sulcus
Foliate papillae
Vallate papilla
Medial sulcus
of the tongue
Dorsum of tongue
Fungiform papilla
Filiform
papilla
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Mouth
B.
Salivary glands
1. Three pairs of
compound
tubuloveolar
glands secrete a
major amount –
about 1 liter of
saliva each day
Figure 23.9a The salivary glands.
Tongue
Parotid
gland
Teeth
Ducts of
sublingual
gland
Parotid duct
Masseter muscle
Frenulum
of tongue
Body of mandible
(cut)
Sublingual
gland
Posterior belly of
digastric muscle
Mylohyoid
muscle (cut)
Submandibular
duct
Anterior belly of
digastric muscle
Submandibular
gland
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Mouth
C.
Teeth
1. Typical tooth
a. Crown –
exposed
portion of
a tooth
and is
covered
by
enamel
Figure 23.11 Longitudinal section of a canine tooth within its bony socket (alveolus).
Enamel
Dentin
Crown
Neck
Dentinal
tubules
Pulp cavity
(contains
blood vessels
and nerves)
Gingival
sulcus
Gingiva
(gum)
Cement
Root
Root canal
Periodontal
ligament
Apical
foramen
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Bone
b. The outer shell
of the tooth is
also covered
by dental
tissues
(greatest
proportion of
the tooth shell
c. Pulp cavity
consists of
connective
tissue, blood,
and lymphatic
vessels and
sensory nerves
Figure 23.10 Human dentition.
Incisors
Central (6–8 mo)
Lateral (8–10 mo)
Canine (eyetooth)
(16–20 mo)
Molars
First molar
(10–15 mo)
Second molar
(about 2 yr)
Deciduous
(milk) teeth
Incisors
Central (7 yr)
Lateral (8 yr)
Canine (eyetooth)
(11 yr)
Premolars
(bicuspids)
First premolar
(11 yr)
Second premolar
(12–13 yr)
Molars
First molar (6–7 yr)
Second molar
(12–13 yr)
Third molar
tooth) Inc.
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(17–25 yr)
Permanent
teeth
2.
Types of teeth
a. Twenty
deciduous
teeth – baby
teeth (does
not include
premolars
i.
Incisors
ii.
Canine
(eyetooth)
iii. Molars
b. Thirty-two permanent teeth
i.
Incisors –
cutting
ii. Canine –
tear and
pierce
iii. Premolars
(Bicuspids)
iv. Molars –
grinding
and
crushing
Pharynx
A.
Bolus – mass of food
B.
Deglutition
(swallowing) moves
food (bolus) from
the mouth to the
stomach
C. Used for digestion
and respiration
Figure 23.13 Deglutition (swallowing). (1 of 5)
Bolus of food
Tongue
Pharynx
Epiglottis
Glottis
Trachea
1 During the buccal phase, the upper
esophageal sphincter is contracted.
The tongue presses against the hard
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palate,
forcing
the food bolus into the
oropharynx.
Figure 23.13 Deglutition (swallowing). (2 of 5)
Uvula
Bolus
Epiglottis
Esophagus
2 The pharyngeal-esophageal phase
begins as the uvula and larynx rise to prevent
food from entering respiratory passageways.
The tongue blocks off the mouth. The upper
esophageal
sphincter
relaxes, allowing food
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to enter the esophagus.
Figure 23.13 Deglutition (swallowing). (3 of 5)
Upper
esophageal
sphincter
Bolus
3 The constrictor muscles of the
pharynx contract, forcing food into
the esophagus inferiorly. The upper
esophageal
© 2013
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(closes) after food enters.
Figure 23.13 Deglutition (swallowing).
Bolus of food
Tongue
Uvula
Pharynx
Bolus
Epiglottis
Epiglottis
Glottis
Trachea
Esophagus
1 During the buccal phase, the upper
esophageal sphincter is contracted.
The tongue presses against the hard
palate, forcing the food bolus into the
oropharynx.
2 The pharyngeal-esophageal phase
begins as the uvula and larynx rise to prevent
food from entering respiratory passageways.
The tongue blocks off the mouth. The upper
esophageal sphincter relaxes, allowing food
to enter the esophagus.
4 Peristalsis moves
food through the
esophagus to the
stomach.
Relaxed muscles
Circular muscles
contract
Upper
esophageal
sphincter
3 The constrictor muscles of the
pharynx contract, forcing food into
the esophagus inferiorly. The upper
esophageal sphincter contracts
(closes) after food enters.
Relaxed
muscles
5 The gastroesophageal
sphincter surrounding the
cardial oriface opens, and
food enters the stomach.
Bolus of food
Longitudinal muscles
contract
Circular muscles contract
Gastroesophageal
sphincter closed
Gastroesophageal
sphincter opens
Stomach
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Bolus
Esophagus
A.
Collapsible, muscular,
mucus – lined tube
1.
About 25 cm (10
inches) long
2.
Extends from the
pharynx to the
stomach
3.
Passage way for
food, pushing the
food toward the
stomach
Esophagus
B.
First segment of the
digestive tube
1.
Upper esophageal
sphincter – helps
prevent air from
entering during
respiration
2.
Lower esophageal
sphincter – also
called cardiac
sphincter junction
between
esophagus and
stomach
Figure 23.13 Deglutition (swallowing). (4 of 5)
4 Peristalsis moves
Relaxed muscles
food through the
esophagus to the
stomach.
Circular muscles
contract
Bolus of food
Longitudinal muscles
contract
Gastroesophageal
sphincter closed
Stomach
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Esophagus
C.
Gastroesophageal
reflux disease (GERD)
1.
Backward flow of
stomach acid up
through the
cardiac sphincter
2.
Treated by
elimination of
excess stomach
acid or by surgery
to strengthen the
LES (cardiac
sphincter)
Figure 23.13 Deglutition (swallowing). (5 of 5)
Relaxed
muscles
5 The gastroesophageal
sphincter surrounding the
cardial oriface opens, and
food enters the stomach.
Circular muscles contract
Gastroesophageal
sphincter opens
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Stomach
A.
Size and Position of
the stomach
1.
2.
The stomach
lies in the
upper part of
the abdominal
cavity under
the liver and
diaphragm
After meals the
stomach is
enlarged
Stomach
B.
Divisions of the
stomach
1.
Fundus – above
the opening of
the esophagus
2.
Body- Central
part
3.
Pylorus – lower
portion
Stomach
C. Sphincter muscles
1. Guard both stomach openings
2. Muscle consisting of circular fibers
3. Cardiac sphincter controls the
opening of the esophagus into the
stomach
4. Pyloric sphincter controls the
opening from the pyloric portion of
the stomach into the first part of the
small intestine
Figure 23.19 Peristaltic waves in the stomach.
Pyloric
valve
closed
Pyloric
valve
closed
1 Propulsion: Peristaltic
waves move from the fundus
toward the pylorus.
2 Grinding: The most
vigorous peristalsis and
mixing action occur close to
the pylorus.
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Pyloric
valve
slightly
opened
3 Retropulsion: The pyloric
end of the stomach acts as a
pump that delivers small amounts
of chyme into the duodenum,
simultaneously forcing most of its
contained material backward into
the stomach.
Stomach
D.
Gastric Muscosa
1.
Chief cells – secrete enzymes of gastric juice
2.
Parietal cells – secrete hydrochloric acid
3.
Endocrine cells – secrete ghrelin – a
hormone that stimulates the hypothalamus
to increase appetite and gastrin which
influences digestive functions
Figure 23.14 Anatomy of the stomach.
Cardia
Fundus
Esophagus
Muscularis
externa
• Longitudinal layer
• Circular layer
• Oblique layer
Serosa
Body
Lumen
Lesser
curvature
Rugae of
mucosa
Greater
curvature
Duodenum
Pyloric sphincter
(valve) at pylorus
Liver
(cut)
Pyloric
canal
Pyloric
antrum
Fundus
Body
Spleen
Lesser
curvature
Greater
curvature
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Figure 23.15a Microscopic anatomy of the stomach.
Surface
epithelium
Mucosa
Lamina
propria
Muscularis
mucosae
Submucosa
(contains
submucosal
Oblique
plexus)
layer
Muscularis
Circular
externa
layer
(contains
Longitudinal
myenteric
layer
plexus)
Stomach wall
Serosa
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Layers of the stomach wall
Figure 23.15b Microscopic anatomy of the stomach.
Gastric pits
Surface epithelium
(mucous cells)
Gastric
pit
Mucous neck cells
Parietal cell
Gastric
gland
Chief cell
Enteroendocrine cell
Enlarged view of gastric pits and
gastric glands
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Figure 23.15c Microscopic anatomy of the stomach.
Pepsinogen
Pepsin
HCI
Mitochondria
Parietal cell
Chief cell
Enteroendocrine
cell
Location of the HCl-producing parietal cells
and pepsin-secreting chief cells in a gastric
gland
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Stomach
E.
Gastric Muscle
1.
Crisscrossing
pattern of smooth
muscle fibers
2.
Stomach wall has
the ability to
contract strongly
at many angles
which causes
mixing action of
this organ.
Stomach
F.
Functions of the stomach
1.
Stores food
2.
Secretes gastric juice
3.
Churns the food, breaking it down into small
particles
4.
Secretes intrinsic factor
5.
Limited amount of absorption – certain
drugs, some water and alcohol and some
short – chain fatty acids
Stomach
6. Destroys pathogenic bacteria
7. Produces the hormone gastrin
8. Regulates the hormone ghrelin which
increases appetite
Small intestine
A.
Introduction
1. Small intestine is a
tube measuring
about 2.5 (1 inch)
in diameter and 6
m (20 feet) in
length.
2. Coiled and looped
Figure 23.28 Mechanisms promoting secretion and release of bile and pancreatic juice.
1 Chyme enter
-ing duodenum
causes duodenal
enteroendocrine
cells to release
cholecystokinin
(CCK) and
secretin.
2 CCK (red
dots) and
secretin (yellow
dots) enter the
bloodstream.
3 CCK induces
secretion of
enzyme-rich
pancreatic juice.
Secretin causes
secretion of
HCO3− -rich
pancreatic juice.
4 Bile salts
and, to a lesser
extent, secretin
transported via
bloodstream
stimulate Liver to
produce bile
more rapidly.
5 CCK (via
blood stream)
causes gallbladder
to contract and
Hepatopancreatic
Sphincter to
relax. Bile Enters
duodenum.
6 During cephalic
and gastric phases,
vagal Nerve stimulates gallbladder to
contract weakly.
CCK secretion
Secretin secretion
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Small intestine
B.
Divisions of the small
intestine
1.
Duodenum
a.
Uppermost
division
b.
Part to which
the pyloric end
of the stomach
attaches
c.
About 25 cm
(10 inches)
long
d.
Shaped like a
C
Small intestine
2. Jejunum – 2.5 m
(8 feet) long
3. Ileum – 3.5 m (
12 feet) long
Small intestine
C.
Wall of the small
intestine
1.
Intestinal ling has
circular folds that
have many tiny
projection call villi
2.
Epithelial cells on
the surface of villi
can be seen by
microscopy to
have a surface
resembling a fine
brush is formed by
microvilli
Figure 23.22b Structural modifications of the small intestine that increase its surface area for digestion and absorption.
Microvilli
(brush border)
Absorptive
cells
Lacteal
Goblet
cell
Blood
capillaries
Mucosaassociated
lymphoid
tissue
Intestinal
crypt
Muscularis
mucosae
Duodenal
gland
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Villus
Enteroendocrine
cells
Venule
Lymphatic vessel
Submucosa
Figure 23.22c Structural modifications of the small intestine that increase its surface area for digestion and absorption.
Absorptive cells
Goblet
cells
Villi
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Intestinal crypt
Figure 23.23 Microvilli of the small intestine.
Mucus
granules
Microvilli
forming the
brush border
Absorptive cell
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 D. Function – Complete Digestion and
food and nutrient absorption
Large Intestine
A.
Size of the Large
Intestine
1.
Diameter is
larger than that
of the small
intestine
2.
Length is 1.5 to
1.8 m (5-6 feet)
Figure 23.29a Gross anatomy of the large intestine.
Left colic
(splenic) flexure
Right colic
(hepatic) flexure
Transverse
mesocolon
Transverse colon
Epiploic
appendages
Superior
mesenteric artery
Descending colon
Haustrum
Ascending colon
IIeum
Cut edge of
mesentery
IIeocecal valve
Tenia coli
Sigmoid colon
Cecum
Appendix
Rectum
Anal canal
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External anal sphincter
Large Intestine
B.
Divisions of the large
intestine
1.
Cecum
2.
Colon
a.
Ascending colon
– lies in a vertical
position, on the
right side of the
abdomen
b.
Transverse colon
– passes
horizontally
across the
abdomen,
below the liver,
stomach and
spleen
Large Intestine
c. Descending colon –
lies in the vertical
position on the left
side of the abdomen
d. Sigmoid colon – that
courses downward
below the iliac crest
(joins the rectum)
Large Intestine
3. Rectum
a. Last part of the intestinal tube
b. Anal canal
c. Mucous lining is arranged in
numerous vertical folds known as
anal columns
1) Each which contains an artery
and a vein
2) Hemorrhoids are enlargements of
the veins in the anal canal
Figure 23.29b Gross anatomy of the large intestine.
Rectal valve
Rectum
Hemorrhoidal
veins
Levator ani muscle
Anal canal
External anal
sphincter
Internal anal
sphincter
Anal columns
Pectinate line
Anal sinuses
Anus
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C. Function of large intestine
1. Absorption of water
Figure 23.2 Gastrointestinal tract activities.
Ingestion
Mechanical
breakdown
• Chewing (mouth)
• Churning (stomach)
• Segmentation
(small intestine)
Digestion
Food
Pharynx
Esophagus
Propulsion
• Swallowing
(oropharynx)
• Peristalsis
(esophagus,
stomach,
small intestine,
large intestine)
Stomach
Absorption
Lymph
vessel
Small
intestine
Large
intestine
Blood
vessel
Mainly H2O
Feces
Defecation
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Anus
Vermiform Appendix
A.
Wormlike tubular
organ
B.
Average 8 to 10 cm
(3 to 4 inches) in
length
C. Its function
1. It contains masses
of lymphoid tissue
2. Plays an important
role in the body
immunity. It also
stores bacteria
upon the need
during digestion
Figure 23.30a Mesenteries of the abdominal digestive organs.
Falciform ligament
Liver
Gallbladder
Spleen
Stomach
Ligamentum teres
Greater omentum
Small intestine
Cecum
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Figure 23.30b Mesenteries of the abdominal digestive organs.
Liver
Gallbladder
Lesser omentum
Stomach
Duodenum
Transverse colon
Small intestine
Cecum
Urinary bladder
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Figure 23.30c Mesenteries of the abdominal digestive organs.
Greater omentum
Transverse colon
Transverse
mesocolon
Descending colon
Jejunum
Mesentery
Sigmoid
mesocolon
Sigmoid colon
Ileum
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Figure 23.30 Mesenteries of the abdominal digestive organs.
Falciform ligament
Liver
Gallbladder
Lesser omentum
Spleen
Stomach
Duodenum
Ligamentum teres
Transverse colon
Greater omentum
Small intestine
Cecum
Urinary bladder
Liver
Lesser omentum
Greater omentum
Transverse colon
Transverse
mesocolon
Pancreas
Stomach
Duodenum
Transverse mesocolon
Transverse colon
Mesentery
Descending colon
Jejunum
Mesentery
Sigmoid
mesocolon
Sigmoid colon
Greater omentum
Jejunum
Ileum
Ileum
Urinary bladder
Rectum
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Visceral peritoneum
Parietal peritoneum
Peritoneum
A. Membrane
covering and
holding in pace
most of the
organs of the
digestive system
B. Mesentery hold
organs together
(fan shape)
Liver
A. Location and
Size of the
Liver
1. Liver is the
largest
gland in the
body
2. Lies under
the
diaphragm
Figure 23.21 The duodenum of the small intestine, and related organs.
Right and left
hepatic ducts
of liver
Cystic duct
Common hepatic duct
Bile duct and sphincter
Accessory pancreatic duct
Mucosa
with folds
Tail of pancreas
Pancreas
Jejunum
Gallbladder
Major duodenal
papilla
Hepatopancreatic
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Duodenum
ampulla and sphincter
Main pancreatic duct and sphincter
Head of pancreas
Figure 23.24 Gross anatomy of the human liver.
Sternum
Nipple
Liver
Bare area
Falciform ligament
Left lobe of liver
Right lobe of liver
Gallbladder
Lesser omentum
(in fissure)
Left lobe of liver
Porta hepatis
containing hepatic
artery (left) and
hepatic portal vein
(right)
Quadrate lobe
of liver
Ligamentum teres
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Round ligament
(ligamentum teres)
Bare area
Caudate lobe
of liver
Sulcus for inferior
vena cava
Hepatic vein (cut)
Bile duct (cut)
Right lobe of liver
Gallbladder
Liver
B. Liver lobes and
lobules
1. Left lobe
2. Right lobe
3. Caudate lobe
4. Quadrate lobe
5. Hepatic
lobules – made
of hepatic cells
Liver
C.
Bile ducts
1.
Small bile ducts
within the liver join
the form two larger
ducts that emerge
from the under
surface of the
organ as the right
and left hepatic
duct
2.
Hepatic duct
merges with the
cystic duct from the
gallbladder to from
the common bile
duct
Liver
D. Functions of the Liver
1. Detoxify various substances
2. Secrete about a pint of bile a
day
3. Important in the metabolism
of proteins, fats (bile salts are
important in the absorption of
fats) and carbohydrates
Liver
4. Produces
important
plasma
proteins and
serves as a site
of blood cell
production
during fetal
development
5. Storage of iron
and vitamins
Gallbladder
6.
Gallbladder
a.
Size and Location
of the gallbladder
i.
Pear shaped
sac
ii.
7 to 10 cm (3-4
inches)long
iii.
Can hold 30 to
50 ml of bile
iv.
Lies under the
surface of the
liver
Gallbladder
b.
Structure of the
gallbladder
1.
Serous muscular
and mucous
layer
2.
similar to the
stomach wall
3.
Surgical removal
of the
gallbladder is
called
cholesystectomy
Gallbladder
C. Functions of the
gallbladder
1.
Stores bile
(fivefold to
tenfold
concentrations)
2.
During digestion
the gallbladder
contracts
ejecting the bile
into the
duodenum of
the small
intestine
Pancreas
A. Size and Location of the Pancreas
1. Grayish pink colored gland about 12
-15 cm (6-9 inches)
2. It resembles a fish with its head and
neck in the C – shaped curved of
the duodenum
3. Extends horizontally behind the
stomach and its tail touching the
spleen
Pancreas
B.
Structure of the pancreas
1.
Composed of two different types of
glandular tissue one exocrine and
endocrine
2.
Has a pancreatic duct which empties into
the duodenum at the same point of the
common bile duct
3.
Contains alpha cells and beta cells
Pancreas
C. Functions of the pancreas
1.
Pancreas secrete the digestive
enzymes found in pancreatic juice –
important part in digestion
2.
Beta cells of the pancreas secrete
insulin (hormone that exerts a major
control over Carbohydrate metabolism)
3.
Alpha cells secret glucagons – which
has a direct opposite effect on
carbohydrate metabolism
Figure 23.27 Activation of pancreatic proteases in the small intestine.
Stomach
Pancreas
Epithelial
cells
Membrane-bound
enteropeptidase
Trypsinogen
(inactive)
© 2013 Pearson Education, Inc.
Trypsin
Chymotrypsinogen
(inactive)
Chymotrypsin
Procarboxypeptidase
(inactive)
Carboxypeptidase
Disorders of the Digestive
System
A. Heartburn
1. Backflow of stomach acid up into
the esophagus
2. Heartburn is often caused by acid
reflux which might be aggravated
by
a. Smoking
b. Obesity
c. Spicy foods
Disorders of the Digestive
System
B. Ulcers
1. Is a craterlike wound or sore in a
membrane caused by tissue
destruction
2. These sores cause gnawing or
burning pain and may ultimately
result in hemorrhage
3. Gastroesophageal Reflux
Disease (GERD)
Figure 23.16a Photographs of a gastric ulcer and the H. pylori bacteria that most commonly cause it.
A gastric ulcer lesion
© 2013 Pearson Education, Inc.
Figure 23.16b Photographs of a gastric ulcer and the H. pylori bacteria that most commonly cause it.
Bacteria
Mucosa
layer of
stomach
H. pylori bacteria
© 2013 Pearson Education, Inc.
Disorders of the Digestive
System
C. Mumps
1. An acute viral disease
characterized by swelling
of parotid salivary glands
2. Can occur in children and
adults (more of a severe
infection in adults)
Disorders of the Digestive
System
D. Tooth Decay
1. Common disease
2. Disease of the enamel, dentin,
and cementum of teeth
3. Results in the formation of
cavity
Disorders of the Digestive
System
E. Appendicitis
1. Caused by the mucous lining
of the appendix becoming
inflamed.
2. If the appendix ruptures, it
will release infectious
material into the abdominal
cavity can cause death.
 Normal appendix compared to abnormal appendix

https://www.youtube.com/watch?v=lnVjXuyM6xk&list
=PLBMkFNFXhVis9AUGNrFJWgSJHAjonB8cK&index=5
 https://www.youtube.com/watch?v=9bnIuKiHdDE&in
dex=4&list=PLBMkFNFXhVis9AUGNrFJWgSJHAjonB8cK
 https://www.youtube.com/watch?v=eKLqFnAmK6c&li
st=PLBMkFNFXhVis9AUGNrFJWgSJHAjonB8cK&index=11
II. Digestion Physiology
A. Digestive Enzymes
1.
Enzymes are proteins which is made up of amino acids
2.
Can denature (not work properly)
3.
Function at a specific pH and temperature
a.
Amylase
1) Found in saliva
2) Optimal pH of neutral or slightly acidic
b.
Pepsin
1) Found in gastric juice (stomach)
2) The optimal pH is 2 (very acidic)
3) Pepsin must have HCl acid to function
Chapter 26
B. Nutrients
1.
Carbohydrates
a. Sugars with C6H12O6 groups
b. Examples
1) Polysaccharides include starches
(from plants) and glycogen (from
animals)
2) Disaccharides include sucrose
lactose and maltose
3) Monoscaccharides (smallest
carbohydrate molecule) glucose,
galactose and fructose
c. Enzymes affecting
carbohydrate digestion
1)Surcease
2)Lactase
3)maltase
Chapter 26
B. Nutrients
2. Proteins
a. Are large chains of amino acids
b. Enzymes affecting protein
digestion
1) Proteases
2) Pepsin
3. Lipids
a. Includes phospholipids and fats
b. Enzymes affecting fats Lipase
Chapter 26
C. Function of the organs
1. Mouth
a. Saliva contains amylase
b. Beginning digestion of
carbohydrates
2. Stomach
a. Gastric juice contains the
enzyme Protease (pepsin)
b. Beginning digestion of
proteins
Chapter 26
C. Function of the organs
3.
Small Intestine
1. Pancreas
a. Releases enzymes into the small
intestine that breaks down proteins
 Produces both enzymes, trypsin
and chymotrypsin
 produces protease
b. Releases enzymes into the small
intestine that breaks down
carbohydrates - amylase
c. Releases enzymes into the small
intestine that breaks down fats - Lipase
Chapter 26
C. Function of the organs
2.
3.
Enzymes produced by the small intestine
a. Peptidase – breaks down proteins into
amino acids
b. Surcease – breaks down sucrose into
glucose and fructose
c. Lactase – breaks down lactose (milk sugar)
into glucose and galactose
d. Maltase – (Malt sugar) – breaks down into
glucose molecules
Bile produced by the liver is released into the
small intestine and completely breaks down
fat
Chapter 26
C. Function of the organs
4. Large Intestine
1. Absorption of water
2. Stores waste material