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Essentials of Human Anatomy & Physiology
Elaine N. Marieb
Seventh Edition
Chapter 15
The Digestive System
and Body Metabolism
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Functions of the Digestive System
 Digestion
Breakdown of ingested food
 Absorption
 Passage of nutrients into the blood
 Metabolism
 Production of cellular energy (ATP)
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Slide 14.1
Gastrointestinal (GI) Tract
• A continuous, hollow coiled tube that
digests food, breaks it down, and absorbs
the fragments through its lining into the
blood
Organs of the Digestive System
Figure 14.1
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Mouth (Oral Cavity) Anatomy
 Lips (labia) – protect
the anterior opening
 Cheeks – form the
lateral walls
 Hard palate – forms
the anterior roof
 Soft palate – forms
the posterior roof
 Uvula – fleshy
projection of the
soft palate
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Figure 14.2a
Slide 14.4
Mouth (Oral Cavity) Anatomy
 Vestibule – space
between lips externally
and teeth and gums
internally
 Tongue – attached at hyoid
& styloid processes, and
by the lingual frenulum
 Frenulum- mem-brane
that secures the tongue
to the floor of the mouth;
limits movement
Figure 14.2a
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Slide 14.5
Mouth (Oral Cavity) Anatomy
 Tonsils
 Palatine tonsils
 Lingual tonsil
Figure 14.2a
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Slide 14.6
Processes of the Mouth
 Mastication (chewing) of food
(mechanical digestion)
 Mixing masticated food with saliva
(chemical digestion)
 Initiation of swallowing by the tongue
 Allowing for the sense of taste
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Slide 14.7
Pharynx Function
 Serves as a passageway for air and
food
 Food is propelled to the esophagus by
two muscle layers
 Food movement is by alternating
contractions of the muscle layers
(peristalsis)
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Slide 14.9
Esophagus
 Runs from pharynx to stomach through
the diaphragm
 Conducts food by peristalsis
(slow rhythmic squeezing)
 Passageway for food only (respiratory
system branches off after the pharynx)
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Slide
Figure 24.10 The Esophagus
Figure 24.10a-c
The Swallowing Process
Figure 24.11a-h
Stomach Anatomy
 Located on the left side of the
abdominal cavity (~10 in long)
 When full holds about 1 gallon of food
 Food enters at the cardioesophageal
sphincter
 Food exits at the pyloric sphincter
(valve) btwn stomach & small intestine
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Slide
Stomach Anatomy
Figure 14.4a
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Slide
Structure of the Stomach Mucosa
Figure 14.4b, c
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Stomach Functions
 Acts as a storage tank for food
 Site of food breakdown
 Chemical breakdown of protein begins
 Delivers chyme (processed food) to the
small intestine
 Produces 2-3L/day of gastric juice (HCl,
enzymes, & mucus)
 Regulated by neural & hormonal factors
Slide
Diseases and Disorders
• Heartburn – occurs when the cardio-esophageal
sphincter fails to close tightly and gastric juice
backs up into the esophagus
• Hiatal hernia – superior part of the stomach
protrudes above the diaphragm allowing juices to
go into the esopahgus
• Vomiting – reverse movement of food, brought
about by a signal from the medulla
• It takes 4 hours for the stomach
to empty after a well-balanced
meal and 6 hours for a fatty
meal
Small Intestine
(4-8 hrs)
 The body’s major digestive organ
 Site of nutrient absorption into the blood
 Muscular tube extending from the
pyloric sphincter to the ileocecal valve
 Suspended from the posterior
abdominal wall by the mesentery
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Slide
Subdivisions of the Small Intestine
“Dogs Just Itch!
 Duodenum
 Attached to the stomach
 Curves around the pancreas (10 in)
 Jejunum
 Attaches to the duodenum (8 ft long)
 Ileum
 Extends from jejunum to ileocecal valve of
large intestine (12 ft long)
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Slide
Regions of the Small Intestine
Figure 24.16a
Chemical Digestion in the Small
Intestine
 Source of enzymes that are mixed with
chyme
Intestinal cells
Pancreas
 Bile enters from the gall bladder
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Slide
Chemical Digestion in the Small
Intestine
Figure 14.6
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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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Microvilli of the Small Intestine
 Small projections of the
plasma membrane
 Found on absorptive cells
Figure 14.7c
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Structures Involved in Absorption of
Nutrients
 Absorptive cells
 Blood capillaries
Figure 14.7b
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Slide
Digestion in the Small Intestine
 Break double sugars into simple sugars
 Complete some protein digestion
 Help complete digestion of starch
 Carry out about half of all protein digestion
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Slide
Digestion in the Small Intestine
(help from the pancreas)
 Pancreatic enzymes play the major
digestive function
 Responsible for fat digestion (lipase)
 Digest nucleic acids (nucleases)
 Alkaline content neutralizes acidic chyme
 Produce insulin
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Absorption in the Small Intestine
 Water is absorbed along the length of
the small intestine
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Slide
Propulsion in the Small Intestine
 Peristalsis is the major means of
moving food
 Segmental movements
 Mix chyme with digestive juices
 Aid in propelling food
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Slide
Figure 24.4 Peristalsis
Figure 24.4
Large Intestine (12-24 hrs.)
 Larger in diameter, but shorter than the
small intestine
 Frames the internal abdomen
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Slide
Large Intestine
Figure 14.8
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Functions of the Large Intestine
 Absorption of water
 Eliminates indigestible food from the
body as feces
 Does not participate in digestion of food
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Slide
Structures of the Large Intestine
 Ileocecal valve – btwn small & large
intestine
 Cecum – saclike 1st part of the large
intestine
 Appendix
Accumulation of lymphatic tissue that
sometimes becomes inflamed
(appendicitis)
Hangs from the cecum
Slide
Structures of the Large Intestine
 Colon
 Ascending – travels up the right side
 Transverse – travel across abdomin
 Descending – travels down the left side
 Sigmoidal colon (aka pelvic colon)
 Rectum – holding area before release of
fecal material
 Anus – external body opening
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Slide
Food Breakdown and Absorption in
the Large Intestine
 No digestive enzymes are produced
 Resident bacteria digest remaining
nutrients
 Produce some vitamin K and B
 Release gases
 Water and vitamins K and B are absorbed
 Remaining materials are eliminated via
feces
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Slide
Propulsion in the Large Intestine
 Sluggish peristalsis
 Mass movements
 Slow, powerful movements
 Occur three to four times per day
 Presence of feces in the rectum causes
a defecation reflex
 Internal anal sphincter is relaxed
 Defecation occurs with relaxation of the
voluntary (external) anal sphincter
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Slide
Digestive Secretion and Absorption of Water
Diseases and Disorders
• Diarrhea – results when water is not
sufficiently absorbed by large intestine (can
be due to bacteria)
• Constipation – results when too much water
is absorbed by the large intestine
Accessory Digestive Organs
 Salivary glands
 Teeth
 Pancreas
 Liver
 Gall bladder
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Slide
Salivary Glands
 Saliva-producing glands
 Parotid glands – located anterior to ears
(mumps is inflammation of the parotis
glands)
 Submandibular glands
 Sublingual glands
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Mumps
Saliva
 Aids in chemical digestion
 Mixture of mucus and serous fluids
 Contains salivary amylase to begin
starch digestion
 Dissolves chemicals so they can be
tasted
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Slide
Teeth
 The role is to masticate (chew) food
 Aids in mechanical digestion
 Humans have two sets of teeth
 Deciduous (baby or milk) teeth
 20 teeth are fully formed by age two
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Teeth
 Permanent teeth
 Replace deciduous teeth beginning
between the ages of 6 to 12
 A full set is 32 teeth, but some people do
not have wisdom teeth
 Teech are named according to their main
function
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Classification of Teeth
 Incisors
 Canines
 Premolars
 Molars
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Classification of Teeth
Figure 14.9
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Regions of a Tooth
 Crown – exposed part
(hardest substance in
the body)
 Outer enamel
 Dentin
 Pulp cavity
 Neck
 Region in contact with
the gum
 Connects crown to
root
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Figure 14.10
Slide
Regions of a Tooth
 Root
 Periodontal
membrane
attached to the
bone
 Root canal carrying
blood vessels and
nerves
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Figure 14.10
Slide
Pancreas
 Produces a wide spectrum of digestive
enzymes that break down all categories of food
 Enzymes are secreted into the duodenum
 Alkaline fluid introduced with enzymes
neutralizes acidic chyme
 Endocrine products of pancreas
 Insulin
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Figure 24.18 The Pancreas
Figure 24.18a-c
Liver
 Largest gland in the body
 Located on the right side of the body
under the diaphragm
 Consists of four lobes suspended from
the diaphragm and abdominal wall by
the falciform ligament
 Connected to the gall bladder via the
common hepatic duct
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The Anatomy of the Liver
Figure 24.19a
Bile
 Produced by cells in the liver
 Composition
 Bile salts
 Bile pigment (mostly bilirubin from the
breakdown of hemoglobin)
 Cholesterol
 Phospholipids
 Electrolytes
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Role of the Liver in Metabolism
 Several roles in digestion
 Detoxifies drugs and alcohol
 Degrades hormones
 Produce cholesterol, blood proteins
(clotting proteins)
 Plays a central role in metabolism
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Slide
Metabolism
• Metabolism – chemical reactions that are
necessary to maintain life
– Catabolism – substances are broken down,
energy released and captured to make ATP
– Anabolism – small molecules come together to
form larger molecules
How to maintain blood glucose
(sugar) levels…
• Blood circulates through the liver and
glucose is removed. If the body has an
abundance, glucose is made into gycogen.
This is called glycogenesis.
• If the body is low on sugar, the liver will
break down the glycogen into sugar. This is
called glycogenolysis.
Carbohydrate metabolism
• Cellular respiration – glucose is broken
down, releasing chemical energy to form
ATP
• Glucose + O2 = CO2 + H20 + ATP
• If too much sugar is in the blood, it si
converted to FAT!
Fat metabolism
• Most of it occurs in the liver
• Fat is broken down into acetic acid. Then it
is oxidized and CO2, H2O, and ATP are
formed.
• This occurs when there are low amounts of
sugar in the blood.
Protein metabolism
• Amino acids (make up proteins) are used to
make ATP only when proteins are over
abundant or carbs. and fats are not
available.
• Amino acids are oxidized and ammonia
(NH3) is given off (secreted). The rest if the
amino acids enter the citric acid cycle.
Gall Bladder
 Sac found in hollow part of the liver
 Stores bile from the liver
 Bile is introduced into the duodenum in
the presence of fatty food
 Gallstones can cause blockages
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Slide
The Gallbladder
Figure 24.21a, b
Diseases and Disorders
• Gallstones occur when bile is stored for too
long and fat crystallizes
• Jaundice – bile enters the blood stream and
tissues become yellow
Processes of the Digestive System
 1. Ingestion – getting food into the
mouth
 2. Food breakdown –(Propulsion) –
moving foods from one region of the
digestive system to another
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Slide
Processes of the Digestive System
 Mechanical digestion
 Mixing of food in the mouth by the tongue
 Churning of food in the stomach
 Segmentation in the small intestine
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Processes of the Digestive System
 Chemical Digestion
 Enzymes break down food molecules into
their building blocks
 Each major food group uses different
enzymes
 Carbohydrates are broken to simple sugars
 Proteins are broken to amino acids
 Fats are broken to fatty acids and alcohols
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Processes of the Digestive System
3. Food movement
 Peristalsis – alternating
waves of contraction
 Segmentation – moving
materials back and forth
to aid in mixing
Figure 14.12
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Slide
Processes of the Digestive System
 4. Absorption
 End products of digestion are absorbed in
the blood or lymph
 Food must enter mucosal cells and then
into blood or lymph capillaries
 5. Defecation
 Elimination of indigestible substances as
feces
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Slide
Processes of the Digestive System
Figure 14.11
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Slide
Nutrition - Take a Class!
 Nutrient – substance used by the body for
growth, maintenance, and repair
 Categories of nutrients
 Carbohydrates: simple sugars, starches,
fiber (fruit, grain, veggies, some milk &
meat)
 Lipids: triglycerides, phospholipids, fatty
acids
 Proteins: amino acids
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Nutrition cont.
• Vitamins: need a balanced diet to obtain
essential vitamins
• Most fxn as a coenzyme (act w/out an enzyme to
complete a rxn)
• Mineral – body requires 7 minerals (Ca, P, K, S,
Na, Cl, Mg)
• Water
What nutrients do for the body
• Carbohydrates – broken down to form ATP
• Lipids – build cell membranes, make
myelin sheath and insulates the body
• Proteins – major structure for building cells
Body Energy Balance
 Energy intake = total energy output
(heat + work + energy storage)
 Energy intake is liberated during food
oxidation
 Energy output
 Heat is usually about 60%
 Storage energy is in the form of fat or
glycogen
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Slide
Metabolic rate
• Basal metabolic rate – the amount of heat
produced by the body per unit of time while at
rest. This represents the energy supply a person
needs to perform essential life activities.
• Ex. 154lb adult has a BMR of 60-72 kcal/hr
• Total metabolic rate – total amount of kilocalories
the body must consume to fuel all ongoing
activities
Factors that influence BMR
•
•
•
•
Surface area, gender, age, and thyroid
Younger people have a high BMR
Smaller people have a lower BMR
Hyperthyroidism – excessive metabolic rate
= thin
• Hypothyroidism – slower metabolic rate =
obese
Diseases and Disorders
• Frostbite – when the body is exposed to low
temperatures. Capillaries constrict to keep
blood deeper for the internal organs.
• Shivering – occurs when internal body
becomes too cold; this produces heat
• Hypothermia – extremely low body temp.
This results from prolonged exposure to the
cold; vital signs decrease
Diseases and Disorders
• If the body is hot, capillaries become flushed with
warm blood, releasing heat. Sweating will occur.
Heat stroke or heat exhaustion can occur.
• Cleft palate – palate does not form properly;
deformities of mouth, nose, and lips
• Cystic fibrosis – excessive mucus impairs activity
of pancreas. Fat and fat-soluble vit. are not
digested
Diseases and Disorders
• PKU – inability to use amino acids in food;
can cause brain damage and mental
retardation
• Gastroenteritis – inflammation of the
gastrointestinal tract; can be caused by
contaminated food
Diseases and Disorders
• Appendicitis – inflammation of the
appendix
• Ulcer – lesion or erosion of mucus
membrane, exposed to secretions of the
stomach