Digestive System
What goes in, must come out.
Major Activities of Digestive System
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Ingestion
Mechanical
Processing
Digestion
Secretion
Absorption
Defecation
Defense
Peristalsis
Organs of the Digestive Tract
 Digestive
parts:
Tract consists of two
 Alimentary
Canal – actual digestive
tract organs
 Accessory Organs – organs that help
in digestion but no food ever enters
Alimentary Canal
mouth
pharynx
esophagus
stomach
small intestine
large intestine
anus
Accessory Organs
salivary glands
teeth
pancreas
liver
gall bladder
Oral Cavity
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Food enters the digestive
system here
Teeth tear, cut and grind
food into small pieces
(mechanical digestion)
Saliva from salivary glands
moistens food
Saliva also contains amylase
that break down large
carbohydrates
Salivary Glands
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Parotid,
submandibular and
sublingual glands
located in the oral
cavity produce the
majority of the saliva
Saliva is mostly water
with mucous
What’s a bolus?
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The bolus is a small mass of chewed food
mixed with saliva. Epiglottis, flap of cartilage,
covers the opening of the larynx to prevent
food from going to lungs. Soft palate raises to
prevent bolus from entering into nasal cavity
Peristalsis
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Peristalsis is the rhythmic contraction of smooth
muscles to move contents through the digestive
tract.
Peristalsis starts in the esophagus where the
bolus is propelled down towards the stomach.
Lower esophageal (cardiac) sphincter is the
opening of the stomach and relaxes allowing
bolus to enter
Peristalsis in Action
Stomach
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Stores ingested food until it is released into the
small intestine
Secretes hydrochloric acid (HCl) and enzymes
(pepsin) that begins protein digestion = chyme
High acidic levels (low pH) kill most bacteria and
other pathogens found in the food we eat
Absorbs vitamin B12, alcohol, aspirin, water, and
caffeine
Facts about the Stomach
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muscular, elastic, pear-shaped
can change size … 12” x 6” and can hold
about 2-4 liters of food
Cardiac sphincter prevents food from
passing back to the esophagus (heartburn)
Stomach empties into the duodenum and is
separated by pyloric sphincter
You re-grow a new stomach lining every
3 days
Layers of the Stomach
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Starting from inside…
 Mucosa – acid and digestive juices
secreted
 Submucosa – connective tissue
 Muscularis – layer of muscle that moves
and mixes stomach content
 Subserosa and serosa – wrapping for
the stomach
Inside of Stomach
Outside of Stomach
The journey….
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After 1 to 3 hours in the stomach, chyme
moves into the small intestine
Strong peristaltic waves propel chyme
through pyloric canal toward pyloric
orifice (the opening between stomach
and small intestine)
Phyloric sphincter controls the rate and
amount of chyme entering intestine
Small Intestine
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Divided into three sections
 duodenum
 jejunum
 ileum
Duodenum
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First section of small intestine
C-shaped and ~ 10 inches long
Complete digestion of food molecules
occurs in the duodenum
Presence of acidic chyme stimulates the
release of pancreatic secretions
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these secretions are clear, basic, and contain
mostly water and some enzymes.
secretions help neutralize stomach acid
Pancreas
Pancreas makes
insulin and digestive
enzymes which are
‘dumped’ into the
duodenum
Insulin regulates
glucose levels and is
related to Diabetes
Microvilli
Increase surface
area of intestine so
more absorption
can occur
Jejunum and Ileum
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Most absorption of the
digested food occurs in the
jejunum
Jejunum is the middle part
of the small intestine
Ileum is the last part of
small intestine and is
primarily responsible for
absorbing salts and vitamin
B12
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the liver is an accessory
organ
produces bile that is
dumped into duodenum.
Bile is basic, contains
water, bile salts, bile
pigments, cholesterol and
enzymes
Absorbs alcohol
Liver
Bile breaks down large fat droplets into
smaller ones so enzymes can digest the fat
Excess bile is stored in the gall bladder
Large Intestine
Large Intestine
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a.k.a. “large bowel” – part of the digestive
system where waste products from food
are collected and processed into feces.
Large Intestine’s Functions:
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reabsorbs water; maintains fluid balance
absorbs certain vitamins
processes undigested material (fiber)
stores waste before it is eliminated
Cecum
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first part of the large intestine
shaped like a small pouch and is located in
the right lower abdomen
it connects the small and large intestines
the cecum accepts and stores processed
material from small intestine and moves it
towards the colon
ileocecal valve is the sphincter between
the two intestines
the appendix extends from the cecum
Vermiform Appendix
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A blind ended tube connected to the cecum
Vermiform in Latin means “worm-like”
The biological purpose of the appendix has
mystified scientists for some time
The most common explanation is that the
appendix is a vestigial structure with no absolute
purpose
Some people are born without an appendix
Sometimes bacteria and indigestible material
become trapped in the appendix causing it to
swell and rupture
Colon
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Shaped like an inverted
“U”
Largest part of the large
intestine
Colon has four sections:
 Ascending colon
 Transverse colon
 Descending colon
 Sigmoid colon
What does the colon do?
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Fiber, small amounts of water, vitamins, etc. mix
with mucus and bacteria and start to form feces
The lining of the colon absorbs most of the
water along with vitamins and minerals
Bacteria chemically break down some fiber for
their own nourishment
Through muscular movement, feces is pushed
along until the sigmoid colon contracts, and then
the feces is moved into the rectum.
The rectum is the final part of the large
intestine. Stool is stored here before being
passed as a bowel motion.