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Essentials of Human Anatomy & Physiology
Elaine N. Marieb
Seventh Edition
Chapter 14
The Digestive System
and Body Metabolism
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Organs of the Digestive System
Figure 14.1
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
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Mouth, pharynx, esophagus, stomach, small
intestine, large intestine.
It does all digestive functions
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Ingests
Digests
Absorbs
Defecates
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Teeth, tongue, large digestive glands like the
liver, gall bladder and pancreas.
Assist with digestive functions
◦ Secrete enzymes
◦ Mechanical digestion
1.
2.
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Ingestion : taking in food
Propulsion: moving food through the
alimentary canal.
Peristalsis: alternate waves of contraction
and relaxation that move food through
the G.I. tract.
Segmentation: Neighboring segments of
the intestine contract and relax
alternately, mixing the food.
3.
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4.
Mechanical Digestion: physically
preparing food for digestion.
Mixing by tongue
Churning in stomach
Segmentation in small intestine.
Chemical Digestion: catabolic
process where large food particles
break down by enzymes. Process =
hydrolysis
5.
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6.
Absorption: transport of end
products from lumen (G.I. Tract) to
the blood.
Happens in the small intestine.
Defecation: elimination of
indigestible substances from the
body.

Why is the epithelium on the gums, hard
palate, and dorsal surface of tongue
keratinized?
◦ Protect from abrasion during eating
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Lips and cheeks

Palate
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What happens during swallowing so that we
do not aspirate food into the lungs?
◦ keep food between teeth when we chew
◦ play a role in speech
◦ hard palate & soft palate
◦ Soft palate rises to close off the nasopharynx
while Epiglottis closes off larynx to block trachea
Mouth (Oral Cavity) Anatomy
Figure 14.2a
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 14.4
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Functions
◦ speech movements
◦ mixes food with saliva
◦ forms food bolus
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What are the function of the intrinsic &
extrinsic muscles of the tongue?
◦ Intrinsic – allows tongue to change shape
◦ Extrinsic – alters the position of the
tongue
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Lingual Frenulum
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Papillae
◦ secures tongue to floor of mouth
◦ limits posterior movements – can’t really swallow
your tongue!
◦ tongue tied = extremely short lingual frenulum –
causes speech distortions – can be surgically cut
to correct
◦ Filiform = rough – provide friction
◦ Fungiform = taste buds – located on sides & apex
◦ Circumvallate = taste buds – row on back of
tongue
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4 functions
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Cleanses teeth
Dissolves food chemicals
Moistens food
Chemical breakdown of starch
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Parotid
◦ Mumps = viral inflammation of parotids – can
cause sterility in males
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submandibular
sublingual
Types of cells
◦ serous cells produce salivary amylase to
breakdown starch
◦ mucous cells produce mucus for lubrication
◦ different glands produce different types of
secretions
Review: Pharynx Anatomy
 Nasopharynx –
not part of the
digestive system
 Oropharynx –
posterior to oral
cavity
 Laryngopharynx –
below the oropharynx
and connected to
the esophagus
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 14.2a
Slide 14.8
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2 muscular layers (circular & longitundinal)
cause peristaltic waves to move food
Oropharynx and laryngopharynx are common
passageways for food, fluids, and air
Nasopharynx has no digestive role (unless
you laugh so hard that you blow your soda
through your nose !!!)
Alternating contractions &
relaxations move food one way
through digestive system
Alternating contractions & relaxations
move food back & forth to break it up
and mix it
 ~10
inches long
 epiglottis routes food into it
 goes through the diaphragm to
join stomach at gastroesophageal
sphincter (aka. Cardioesophageal
sphincter)
 Hiatal
hernia, heartburn,
esophagitis, & esophageal
ulcers: page 449
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GERD =
gastroesophageal
reflux disease
Heartburn is a
symptom of this
Also called acid
reflux
Includes full body digestive system diagram
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Function: storage tank
Site of mechanical digestion
Chemical breakdown of proteins begins
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Creamy semifluid mass of ingested, partially
digested food
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In shorter or more obese people:
◦ High and horizontal
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In taller or thinner people:
◦ Elongated vertically (like a J shape)
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~ 10 inches long – on left side of abdominal
cavity
can hold 1.5 L to 4.0 L of food
Rugae – large longitudinal folds that help mix
food in stomach
Know ALL structures on diagram
Stomach Anatomy
Figure 14.4a
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
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Pyloric sphincter: controls stomach emptying
into small intestine
What important substance is produced by the
parietal cells of the stomach & what does it
do?
◦ Intrinsic factor – necessary for vitamin B12
absorption

What blood disorder can absence of this
substance lead to?
◦ Pernicious anemia
 Mucosal
Barrier – important 3
factors
◦ Thick coating of alkaline mucus
◦ Tight junctions of epithelial cells
◦ Epithelium is completely
renewed ~3 days

Gastric Ulcers
◦ Erosion of stomach wall
◦ Causes: H.pylori bacteria,
hypersecretion of HCl or pepsin,
hyposecretion of mucus,
dietary/smoking/stress factors
contribute
◦ Danger: perforation of stomach wall
followed by peritonitis and
hemorrhage
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Stomach empties in 4-6 hours – know this
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6 meters long (~21 feet) but only 1 inch in
diameter
suspended by mesentary in the abdominal
cavity
3 sections of the small intestine
◦ Duodenum: joins stomach at pyloric sphincter,
~10 inches, curves around head of pancreas
◦ Jejunum: ~8 feet
◦ Ileum: ~12 feet, joins large intestine at ileocecal
valve
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Function: all nutrient absorption
Huge surface area due to length &
modification
◦ Plicae circulares: deep folds that force chyme
to spiral – mixes it and slows movement – folds
do NOT disappear when filled with food – contain
Peyer’s patches (lymphatic glands)
◦ Villi: fingerlike projections – increase SA for
absorption
◦ Microvilli: tiny projections – increase SA &
release digestive enzymes
Villi of the Small Intestine
 Fingerlike
structures formed
by the mucosa
 Give the small
intestine more
surface area
Figure 14.7a
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Slide
Microvilli of the Small Intestine
 Small projections of the
plasma membrane
 Found on absorptive cells
Figure 14.7c
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
Structures Involved in Absorption of
Nutrients
 Absorptive cells
 Blood capillaries
 Lacteals (specialized
lymphatic capillaries)
Figure 14.7b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
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Liver has multiple functions: metabolic &
regulatory
Only digestive function is to produce bile for
export to the duodenum
◦ Bile is used to emulsify fats – distribute fat into
solution to be accessible to digestive enzymes
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Has 4 lobes & weighs about 3 pounds
Very vascular (since one of its other functions
is to detoxify blood!)
It is the largest gland in your body
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Hepatocytes:
◦ Produce bile
◦ Pick up nutrients to process (example: convert
glucose to glycogen for storage)
◦ Store vitamins ADEK
◦ Detoxify substances in blood
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Kupffer cells
◦ Phagocytes that remove debris from blood
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Hepatitis: acute inflammation of liver –
usually caused by a virus – multiple types:
some transmitted by contaminated food or
water, some transmitted sexually
Cirrhosis: chronic inflammation of liver – can
be caused by multiple things: alcoholism,
toxins, ongoing hepatitis
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4 inches long
Thin walled, greenish sac
Stores & concentrates bile
Sphincter of Oddi regulates release of bile
into small intestine
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Principal enzyme producing organ of the
digestive system
2 types of cells
◦ Acinar – secrete pancreatic enzymes (digestive)
◦ Islets of Langerhan’s – secrete insulin & glucagon to
regulate blood glucose
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Bile & pancreatic juice enter SI together
through Sphincter of Oddi
Chemical Digestion in the Small
Intestine
Figure 14.6
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
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~5 feet long
Major function: dry out indigestible
substances by absorbing water – then
eliminates feces
Subdivisions (see on diagram): Cecum,
appendix, ascending colon, transverse colon,
descending colon, sigmoid colon, rectum,
anus
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Appendix can be a trouble spot: can be a
spot for bacteria to accumulate, multiply,
cause infection, then rupture
◦ Signs: pain in umbilical region, nausea, lower right
quadrant pain (rebound pain)
◦ Surgical removal before rupture!
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Internal,
involuntary
External,
voluntary
Processes of the Digestive System
Figure 14.11
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide
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Mechanoreceptors: responds to stretch of
the organ walls
Osmoreceptors: responds to solute
concentration and pH
Chemoreceptors: responds to the presence
of end products
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Salivary amylase is an enzyme that begins
the digestion of starches
There are 4 helpful substances in saliva that
help protect/heal
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IgA antibodies
Lysozyme
Glandular virus blocker
Growth factor
The average daily output of saliva is 1 to
1.5 L
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Fear/excitement cause dry mouth
◦ When SNS is activated, it causes vasocontriction of
BV to the salivary glands and inhibits saliva release

Halitosis: Any disease process that inhibits
saliva secretion will result in halitosis since
decomposing food particles accumulate and
bacteria flourish (bacterial waste cause the
odor!!)
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Structures involved in swallowing:
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Tongue
Soft palate
Pharynx
Esophagus
22 other muscles
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Hard palate does not fuse completely so
mouth is open into nasal cavity. Seriousness
is that infants cannot suck properly to obtain
nourishment. They will have to be fed
through a stomach tube.

What 3 things does your body do to cause
food to be routed into the digestive tract
only?
◦ Tongue blocks off mouth
◦ Soft palate rises to close off nasopharynx
◦ Epiglottis closes off laryngeal opening to
respiratory tract

How long does it take food & fluids to reach
the stomach?
◦ Fluids: 1-2 seconds
◦ Food: 4-8 seconds
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What is the only stomach function essential to
life?
◦ Secretion of intrinsic factor
◦ If a gastrectomy is performed, B12 must be injected
to prevent pernicious anemia
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What is plasticity & why is it important?
◦ Stress/relaxation response: ability of smooth
muscle to be stretched & then relax
◦ Prevents tension from causing the stomach to
contract expulsively as it fills with food/fluids
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It takes the stomach 4-6 hours to empty
completely
The rate of gastric emptying depends on:
◦ Contents of duodenum as well as state of food
digestion in stomach.
◦ Duodenum must be empty enough to receive chyme
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High carbohydrate meals move rapidly
through the duodenum
Fats form an oily layer on top of the chyme
and cause release of enterogastrone which
slows digestion
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Irritation of the stomach activates the emetic
center in the medulla.
Causes reverse peristalsis, moving
chyme/partially digested food out of the
stomach and in some cases, the small
intestine.
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The enzyme called rennin is only produced by
infants.
This enzyme helps with milk digestion by
solidifying the milk.
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Alcohol and aspirin are 2 of the commonly
ingested substances that can be absorbed
directly into the blood stream through the
stomach mucosa.
Other nutrients are absorbed in the SI during
their 3-6 hour journey.
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Bile salts emulsify fats
◦ Remember: bile is produced by the liver & stored in
the gall bladder
◦ Bilirubin gives bile its yellowish-green color
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Urobilinogen is the breakdown product of
bilirubin that gives feces their brown color
(feces would be grayish-white without it!)
(SORRY – no pictures!)
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Caused by a decline or absence of intestinal
lactase
Symptoms are bloating, gas, stomach upset,
& diarrhea
Lactase capsules can be taken when eating
dairy products to help with this.
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Immature intestinal mucosa allows intact
proteins across the membranes.
Immune system doesn’t recognize the
antigens on the proteins & attacks them.
◦ These early food allergies usually disappear as
mucosa matures.
◦ This is the reason why infants should not be started
on solids foods too early – also the types of solid
foods they eat affect this.
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Insoluble cellulose compounds that are
indigestible by our digestive system
Fiber increases the strength of the colon
contractions and holds water to soften the
feces
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Bacteria in your LI have 5 main byproducts:
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H2 gas
CO2 gas
CH4 gas (methane)
H2S (hydrogen sulfide – rotten egg smell!)
Vitamins K and some B vitamins
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Feces are semisolid products delivered to the
rectum for excretion
They contain undigested food, residues,
mucus, cells, bacteria, and water
No diagrams