What do you know about the
Digestive System?
Think-Pair-Share
 On a scratch sheet of paper,
jot down some thoughts
about what you know about
the digestive system
 Be prepared to share your
ideas…
Chapter 14
Course of Study
10.) Identify structures and functions of the
digestive system.
 Tracing
the pathway of digestion from the
mouth to the anus using diagrams
 Identifying disorders affecting the digestive
system
 Examples: ulcers, Crohn's disease, diverticulitis
Next Slide…(Picture in your Notes) Be prepared to
explain this step by step on the test!
Anatomy of the Digestive System
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AKA: Gastrointestinal (GI) Tract
Performs the whole menu of
digestive functions (ingests, digests,
absorbs, & defecates)
Is a continuous, coiled, hollow,
muscular tube that winds through the
ventral body cavity and is open at
both ends
Organs include: mouth, pharynx,
esophagus, stomach, small intestine,
& large intestine
In a cadaver, the alimentary canal is
approximately 9m long, but in a living
person, it is considerably shorter
because of its relatively constant
muscle tone
Food material within this tube is
technically outside the body, because
it has contact only with cells lining
the tract and the tube is open to the
external environment at both ends.
Alimentary Canal
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Includes teeth, tongue, &
several large digestive
glands
Assist the process of
digestive breakdown
Accessory Digestive
Organs
Mouth
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Food enters the digestive tract through the mouth or “oral cavity”
Mucous membrane-lined cavity
As food enters the mouth, it is mixed with saliva and masticated
(chewed)
The cheeks and closed lips hold the food between the teeth
during chewing and the tongue continually mixes food with saliva
and initiates swallowing.
Thus, the breakdown of food has begun before it even leaves the
mouth!
Also, as you already know, the papillae containing taste buds on
the tongue surface allow us to enjoy and appreciate food as it is
eaten….thank goodness
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Mouth
Parts include:
 Lips(labia): protect its
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anterior opening
Cheeks: Form its lateral
walls
Hard Palate: forms its
anterior roof
Soft Palate: forms its
posterior roof
Uvula: Fleshy fingerlike
projection of the soft palate
Tongue: Occupies the floor
of the mouth…has bony
attachments like the hyoid
bone and the styloid
process in the skull
Lingual frenulum: secures
the tongue to the floor of
the mouth and limits its
movements (short
frenulum=tongue tied in
children…gets cut)
Tonsils: part of the body’s
defense system
Pharynx
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Subdivided into the:
1.
2.
3.
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Nasopharynx: Part of the respiratory
passageway
Oropharynx: Posterior to the oral cavity
Laryngopharynx: Continuous with the
esophagus below
Walls of the pharynx contain to skeletal
muscle layers
 The cells of the inner layer run
longitudinally
 The cells of the outer layer run around the
wall in a circular fashion
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Alternating contractions of these two
muscle layers propel food through the
pharynx into the esophagus below
This propelling mechanism is called
Esophagus
“Gullet”
 Runs from the pharynx
through the diaphragm to
the stomach
 About 25 cm (10in) long
 It is essentially a
passageway that
conducts food by
to the
stomach
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Stomach
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C-shaped
On the left side of the
abdominal cavity nearly hidden
by the liver and the diaphragm
25cm (10in) long, but its
diameter depends on how much
food it contains
When it is full, it can hold about
4 liters (1 gallon) of food…when
it is empty, it collapses inward
on itself
Acts as a temporary “storage
tank” for food as well as a site
for food breakdown
Stomach
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Physical Breakdown:  Chemical Breakdown:
 Besides the longitudinal and
circular muscle layers, its wall
contains a third obliquely
arranged later in the
muscularis external…this
arrangement allows the
stomach not only to move food
along the tract, but also to
churn, mix and pummel the
food, physically breaking it
down to smaller fragments
 Chemical breakdown of proteins
begins in the stomach, a few
ways:
○ The mucosa of the stomach
produces large amounts of mucus
○ The lining of the stomach is dotted
with millions of deep gastric pits,
which lead into gastric glands that
secrete the solution called “gastric
juices”
 Chief cells produce protein-
digesting enzymes, mostly
pepsinogens, and parietal cells
produce corrosive hydrochloric
acid
 After food has been processed in
the stomach, it resembles heavy
cream and is called “chyme”
 Chyme enters the small intestine
through the pyloric sphincter
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The body’s major digestive organ
Within its twisted passageways,
usable food is finally prepared for
its journey into the cells of the
body
It is the longest section of the
alimentary tube, with an average
length of 2.5-7meters (8-18 feet)
in a living person
Except for the initial part of the
small intestine, the small intestine
hangs in sausage-like coils in the
abdominal cavity
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Has 3 subdivision:
 Duodenum 5% of length
 Jejunum 40% of length
 Ileum 60% of length
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 and
prevents the small intestine from
being overwhelmed
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Chemical Digestion in the Small Intestine
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The duodenum has interesting features
 Some enzymes are produced by the
intestinal cells of the intestine
 More important enzymes are produced by
the pancreas which are ducted into the
duodenum through the pancreatic ducts,
where they complete the breakdown of
foods in the small intestine
Bile (formed by the liver) also enters the
duodenum through the bile duct
Absorption in the Small Intestine
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Nearly all food absorption occurs in the small intestine
The small intestine is well suited for its function. It has
3 structures that increase the absorptive surface
tremendously:
 Microvilli
○ Tiny projections of the plasma membrane of the mucosa cells
that give the cell surface a fuzzy appearance; sometimes referred
to as the “brush border”
 Villi
○ Fingerlike projections of the mucosa that give it a velvety
appearance and feel…within each villus is a rich capillary
bed…the digested foodstuffs are absorbed through the mucosal
cells into the capillary beds.
 Circular Folds
○ Deep folds of both mucosa and submucosa layers
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All of these structural modifications increase the
surface area and amount of food absorbed!
Much larger in diameter than the small
intestine but shorter in length…about
1.5m (5 feet).
 Its major functions are to dry out the
indigestible food residue by absorbing
water and to eliminate these residues
from the body as feces.
 It frames the small intestine on 3 sides
and has the following subdivisions:
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 Cecum, appendix, colon, rectum, anal canal
Path of Food
Through the Body
You are a piece of your favorite
food…explain the path you take
through the body from your oral
cavity (mouth) to your
anus…give specific details of
things you would go through as
a piece of food…
Accessory Digestive Organs
Salivary Glands
 Teeth
 Pancreas
 Liver
 Gallbladder
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Salivary Glands
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Three pairs of salivary glands empty their
secretions into the mouth
 Parotid gland:
○ Lie anterior to the ears. Mumps, a common childhood
disease in an inflammation of the parotid glands
 Submandibular glands & Sublingual glands:
○ Empty their secretions into the floor of the mouth
through tiny ducts…their secretion is saliva-a mixture of
mucus and serous fluids.
 The mucus moistens and binds food together in a mass called
a bolus, which makes chewing and swallowing easier.
 The serous contains an enzyme, salivary amylase, that begins
the process of starch digestion in the mouth.
○ Saliva also contains substances such as lysozyme and
antibodies that inhibit bacteria.
○ Last, but not least, saliva dissolves food chemicals so
they can be tasted! Thank Goodness!
Teeth
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Used to masticate or chew by opening and closing our
jaws and moving them from side to side while continually
using our tongues to move the food between our teeth
Teeth tear and grind the food, breaking it down into smaller
fragments
By the age of 21, two sets of teeth have been formed:
 Baby teeth: AKA Deciduous teeth, begin to erupt around six
months and a baby has a full set of teeth by 2 years
 Adult teeth: AKA Permanent teeth, as this second set of teeth
enlarge and develop, the roots of the baby teeth are reabsorbed,
and between ages 6-12 they loosen and fall out. All of the
permanent teeth but the third molars have erupted by the end of
adolescence…the third molars “wisdom teeth” emerge later,
between the ages of 17-25. Although there are 32 permanent
teeth in a full set, the wisdom teeth often fail to erupt and
sometimes are even absent!
Teeth
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Classified according
to shape and
function as incisors,
canines, premolars,
and molars
 Incisors: adapted for
cutting
 Canines: “eye-teeth”
tearing or piercing
 Premolars and
molars: grinding
Teeth
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A tooth consists of 2 major
regions, the crown and the root
The enamel-covered crown is
the exposed part of the tooth
above the gum
Enamel is the hardest
substance in the body and is
fairly brittle because it is heavily
mineralized with calcium salts
The portion of the tooth
embedded in the jawbone is the
root
The root and the crown are
connected by the tooth region
called the neck
Pancreas
Soft, pink, triangular gland
that extends across the
abdomen from the spleen
to the duodenum
 Produces enzymes that
break down all categories
of digestible food
 The pancreatic enzymes
are secreted into the
duodenum in an alkaline
fluid, which neutralizes the
acidic chyme coming in
from the stomach
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Liver
Largest gland in the body
Located under the diaphragm
to the right side of the body
and almost completely covers
the stomach
 It is one of the body’s most
important organs…it has many
metabolic and regulatory roles
 Its digestive function is to
produce bile…bile leaves the
liver through the common
hepatic duct and enters the
duodenum through the bile
duct
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Bile
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Yellow-to-green, watery
solution that contains many
components, but of the
many only bile salts and
phospholipids aid the
digestive process
Bile does not contain
enzymes, but its bile salts
emulsify fats by physically
breaking large fat globules
into smaller ones, thus
providing more surface
area for the fat-digesting
enzymes to work on
Gallbladder
Small, thin-walled green sac that snuggles in a shallow fossa in the
inferior surface of the liver
 When food digestion is not occurring, bile backs up the cystic duct and
enters the gallbladder to be stored
 While being stored in the gallbladder, bile is concentrated by the
removal of water
 Later, when fatty food enters the duodenum, a hormonal stimulus
prompts the gallbladder to contract and spurt out stored bile, making it
available for use again
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Overview of Gastrointestinal Processes
and Controls
Ingestion
1.
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Food must be placed in the mouth to be acted
on…this active, voluntary process is called
ingestion
Propulsion
2.
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If foods are to processed by more than one
digestive organ, it must be propelled from one
organ to the next (peristalsis-discussed already)
Food Breakdown-Mechanical
3.
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Mixing of food in the mouth, churning of food in the
stomach, and segmentation (movement in one
direction) in the small intestine are all mechanical
food breakdown…physically prepares food by
physically breaking it down into smaller particles
Overview of Gastrointestinal Processes
and Controls
Food Breakdown-Chemical
4.
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The process of large food molecules being broken
down to their building blocks by enzymes is called
chemical digestion
Absorption
5.
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Transport of digested end products from the lumen
of the GI tract to the blood or lymph is
absorption…for absorption to occur, the digested
foods must enter the mucosal cells by active or
passive transport…small intestine is major
absorptive site
Defecation
6.
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Elimination of indigestible residues from the GI tract
through the anus in the form of feces
Disorders of the
Digestive System
1. Ulcers
2. Crohn’s disease
3. Diverticulitis
4. Impacted teeth
5. Gallstones
6. Heartburn
7. Pancreatitis
8. Appendicitus
9. Celiac disease
10.Hernia
11.Lactose intolerance