Digestive System
Chapter 14
Digestive system
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Divided into two parts:
1. Alimentary canal (aka GI tract)
– Path that the food takes through the body
– Performs all digestion functions (ingest,
digest, absorb, defecate)
– In a cadaver the length is about 9-10m
• Shorter when living….Why?
– Organs included?
Digestive System
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2nd part = Accessory organs
– Assist in the digestive system process in
various ways
– Organs included: Teeth, Tongue, Salivary
Glands, Liver, Gallbladder, Pancreas,
Spleen
Mouth
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aka Oral Cavity
Where food enters the body and
digestion begins here.
– How?
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Teeth (mechanical) and saliva
(chemical)
What role do the following play in the
mouth?
– Lips, cheeks, uvula
Tongue
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Mostly muscle tissue
– What type of muscle would it be?
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Frenulum – connects the tongue to the
bottom of the mouth
– What could be a problem if this is too short or
long?
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What is the purpose of the tongue?
Taste and move food around
Papillae – rough projections that contain taste
buds
– Why would these be rough?
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Four types of taste buds – sweet, sour, salt,
bitter
Palate
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2 sections
Hard Palate
– What bone would make this up?
– Anterior Portion
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Soft Palate
– Posterior Portion – mostly a muscular arch
– This and the uvula are drawn up during swallowing
• Why is this important?
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Blocks off the nasal passage during
swallowing
Tonsils
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Play a role in the defenses of the body
Two types:
Lingual – at the base of the tongue
– Used as anchor, covered by lymphatic tissue
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Palatine – Located on the posterior sides
of the tongue
– These are the ones removed when you have
tonsilitis
Teeth
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Used to mechanically breakdown food
– aka masticate, aka chewing
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2 sets
Primary (baby) – 10 on each jaw
– What happens to these?
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They are lost
– The roots are resorbed and teeth are pushed
out by secondary teeth
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Secondary (permanent) – 16 on each jaw
– Begin to appear around age six
Secondary Teeth
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Incisors – 8, front teeth
– Function?
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Cuspids (Canine) – 4, sharper teeth (fangs)
– Function?
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Bicuspids (premolar) – 8, behind cuspids, a bit
flatter
– Function?
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Molars – total of 12, back teeth, much flatter
(4 first, 4 Second, 4 Third)
– Third also known as wisdom teeth
– Function?
Tooth Structure
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Crown – above gums
Root – below gums
Enamel –
– Hardest substance in the body (but brittle) and
cannot be replaced
– What problem does this pose?
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Pulp cavity – Blood supply and nerves
Dentin – deep to the enamel and surrounds
the pulp cavity
Salivary Glands
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Main Secretions
– Amylase – breaks down large starch and
glycogen molecules
– Mucus –
•What is its purpose?
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Bind food particles and lubricate
alimentary canal
What triggers secretions?
Autonomic nervous system
Salivary Glands – 3 different
glands
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Parotid – Located anterior and inferior to
the ear
– Secretes saliva rich in amylase
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Submandibular – Located where?
– Secretes thicker saliva than parotid.
•Why thicker?
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Sublingual – Located where?
– Secretes primarily mucus
Pharynx
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Connects nasal and oral cavities with the
esophagus
Contains the epiglottis
– What is this?
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Flaplike structure used to seal off trachea
during swallowing.
Performs the swallowing reflex
Oral Cavity ?’s
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In comparison to bone, why is enamel
stronger and more brittle?
Differentiate between the parotid,
submandibular, and sublingual salivary
glands.
Why would it be a problem if the tongue
was not skeletal muscle tissue?
Why is the uvula important? (2 reasons)
Describe the teeth of a 12 year old girl.
Steps of Swallowing
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Soft palate raises
Hyoid and larynx raise causing the epiglottis
to close off larynx
Tongue compresses against the soft palate,
sealing the oral cavity from the pharynx
Longitudinal muscles pull the pharynx up
toward the food
Muscles of the lower pharynx relax to open
the esophagus
Peristaltic wave forces food into the
esophagus
Peristalsis
Wall Structure
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The rest of the alimentary canal is really just a
long coiled tube with 4 layers.
Mucosa –inner most layer
– Secretes mucus and enzymes
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Submucosa – contains blood vessels
– Carries nutrients to surrounding tissues but also
nutrients away during absorption.
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Muscular layer – contains circular and
longitudinal muscles
– Moves food through the system
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Serosa – outer layer, secretes serous fluid
– Why is this important?
Esophagus
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Connects pharynx to stomach
– Function?
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Found posterior to the trachea
Ends at cardioesophageal sphincter
– What is a sphincter?
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Ring of muscle that is contracted unless
opened for physiological function
– This one connects the stomach and the
esophagus, what will its function be?
– What will happen if it is not functioning all the
way?
Stomach
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Found on the upper left side of the abdominal
cavity
What happens in the stomach?
– Food is mixed with gastric juices to promote
chemical digestion, very little absorption
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Size is small when empty, yet it can hold up to
4 liters of food.
– How?
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Interior of stomach is lined with large folds
called rugae
– These unfold and the stomach has more area
Stomach
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Regions of the stomach
•Cardiac – near cardioesophageal sphincter
•Fundic – anterior portion (curvature above ces)
•Body – Main region
•Pyloric – posterior portion, near pyloric sphincter
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Stomach ends at Pyloric Sphincter
– What does this control?
Gastric Juice
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4 Components
– Pepsin – main component – digests protein
– Pepsinogen – inactive form of pepsin
– Hydrochloric Acid – converts pepsinogen to
pepsin
– Mucus – lubrication and protection
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Regulated by autonomic nervous system
When this is mixed with food it is called
chyme
Small Intestine
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The largest part of the alimentary canal
– Anywhere from 2.5m to 7m in length
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4 major functions:
Receives secretions from the pancreas
and liver
Completes digestion of chyme
Absorbs products
Transports residues to large intestine
Small Intestine
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3 subdivisions
– Duodenum - smallest section, comes just
after stomach
• Receives food from stomach, and secretions
from pancreas and and liver/gallbladder
– Jejunum – middle section
• Continues digestion, most absorption takes
place here
– Ileum – last and largest section
• Prepares residue for large intestine
Small Intestine
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Walls are well suited for absorption
Have folds, villi, and microvilli
– What are these going to do?
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Greatly increase surface area
Pancreas
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Located near posterior abdominal wall
inferior to stomach
3 important functions
Secretes pancreatic juice into the
duodenum. (where is this?)
– PJ contains amylase, lipase and nuclease
• What are these and what will these do?
– PJ is also very basic (high pH)
• Why is this important?
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What other important function?
Liver
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Located in superior medial part of abdominal
cavity
Very large and lobed (largest gland in body)
One of the most important glands in the body
Multiple Functions (thought to have over 500)
– Many having to do with the filtering and regulation
of many compounds in the blood
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Digestive functions
 Produce and secrete bile (huge in digestion of
fats)
 Secretes it into the duodenum
Bile
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Consists of:
1. Water
2. Bile pigments
 Two types biliverdin (green) and bilirubin (yellow)
 Which one is bad?
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3. Bile salts
 Only part of the bile that has digestive function
 Emulsification
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4. small amounts of other compounds
(electrolytes, cholesterol, phospholipids)
Gallbladder
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Storage area
– What do you think it stores?
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Bile (between meals)
– Reabsorbs water to concentrate it
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If stored too long, gall stones may form
Large Intestine
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Shorter than the small intestine (~1.5m)
Begins at cecum, ends at anus (has two
sphincters)
– Why would it have two?
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Divided into four sections: ascending,
transverse, descending, sigmoid colon
Lacks villi
Little digestive function
– absorbs water and electrolytes
– Eliminates food residue as feces
Questions
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If a person had a condition which limited their ability
to produce hydrochloric acid in the stomach, how
might this affect digestion and why?
Why would it be a problem if a person’s intestinal
walls were completely flat?
Why would storing bile for too long in the gall bladder
cause gallstones?
What would result if a person did not produce much
mucus in the stomach?
Thinking about the contents of the stomach, what
might happen to a person with a cardioesophageal
sphincter that does not close completely?
Disorders of the Digestive system
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What are these disorders and what
causes them?
– Diarrhea
– Peptic Ulcers
– Emesis
– Constipation
– Pancreatitis
– Heartburn
– Diverticulosis
– Jaundice