The Digestive
System
A D VA N C E D H U M A N A N AT O M Y
Introduction
 General function: physical /chemical breakdown of
foodstuffs so it can be absorbed into the bloodstream
and used by the cells/ tissues and eliminate nondigestible substances produced during metabolism
 Digestion: process of changing foodstuffs into usable
substances
 Absorption: transfer of nutrients into the blood stream
Digestive Processes
 Ingestion: process of taking food into the digestive tract
 Propulsion: process of moving food through the alimentary
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canal (swallowing, peristalsis)
Mechanical digestion: physical preparation of food for
chemical digestion; mastication, mixing of food with saliva
by tongue, churning and mixing of food in stomach,
segmentation in intestine
Chemical digestion: catabolic process in which large food
molecules are broken down into smaller molecules by
enzymatic hydrolysis
Absorption: transport of digested end products from the GI
tract into the capillaries and lymph vessels
Defecation: elimination of indigestible materials and waste
from the body
Alimentary Canal
 Gastrointestinal Tract (GI)
 Digests and absorbs food
 Coiled, hollow, muscular
tube with 2 openings
 Approximately 30 feet long
 Includes: mouth, pharynx,
esophagus, stomach, small
intestine, large intestine
Oral Cavity
 Mouth: root stoma = mouth
 Receives and tastes food
 Physical breakdown of food
 Partial digestion by saliva
 Lubrication of food
 Deglutition: the act of swallowing
 Hard palate: bony structure,
roof of mouth, separates mouth
from nasal cavity
Pharynx/Esophogus
Passageways 10 inches long; food only here 4-8 seconds;
no chemical changes take place
 Pharynx: throat, tube that carries food and air
 Epiglottis: flap that covers the trachea when food or
water is swallowed
 Esophagus: muscular tube dorsal to the trachea; carries
food to the stomach by rhythmic wavelike motion
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Peristalsis: progressive wave-like smooth muscle contraction,
distention
Stomach
 Food stays 3-4 hours for physical and chemical
breakdown
 Abdomen: stomach is located in the Left Upper
Quadrant (LUQ)
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Peritoneum: membranes that line abdomen, decreases friction
of organs (peritonitis)
Mesentery: greater and lesser omentum forms protective
covering that insulates organs and holds them in place
Stomach (ctd.)
 Stomach
 Fundus, body, antrum
 Rugae: folds in stomach to increase
surface area
 Sphincters: prevent reflux
Cardiac- ring of muscle where esophagus
and stomach join; keeps stomach contents
from moving up into the esophagus
 Pyloric- ring like muscle between the stomach
and small intestine; keeps food in stomach 30
minutes to 4 hours so that digestion can occur
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Gastric enzymes: pepsin (protein), rennin,
lipase (fats), HCl (kills bacteria, helps in
absorption of Fe, activates pepsin)
Chyme: gastric juices plus digested food
Small Intestine
 Approximately 21 feet long
 1 inch in diameter
 80% of absorption occurs
here
 3 sections
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Duodenum
Jejunum
Ileum
 Enzymes stimulate
intestinal secretions
 Hormones inhibit intestinal
secretions
 Peyer’s patches: lymph
nodes in intestine to aid in
defense/protection
Duodenum
 1st 10-12 inches
 Ducts from pancreas and
gallbladder (sphincter of
Oddi) enter here
 Receives chyme
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Pancreatic juices: amylopsin
(sugars), trypsin (proteins),
lipase (fats)
Gallbladder: bile (emulsifies
and breaks down fats)
Intestinal juices:
maltase/sucrase/lactase
(breakdown sugars)
Jejunum and Ileum
 Jejunum
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Middle portion; 8 feet
partially responsible for absorbing nutrients into the bloodstream.
It is lined with finger-like projections that are called villi, that move
nutrients, vitamins and minerals from the intestine to the bloodstream
 Ileum
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Final 12 feet
Connects to large intestine at cecum
Process of digestion completed
Absorbs bile acids, which are returned to the liver to be made into more
bile, then stored in the gallbladder for future use in the duodenum.
Absorbs vitamin B 12 , which the body uses to make nerve cells and red
blood cells.
The Digestive
System
A D VA N C E D H U M A N A N AT O M Y – DAY 2
Quick Review
 Ingestion,
Propulsion, Digestion
(mechanical and
chemical),
Absorption
 Mouth  Pharynx 
Esophogus (Epiglottis
helps direct traffic!) 
Stomach 
Duodenum 
Jejunum  Ileum
Peristalsis
• Wavelike ripple of smooth muscle
• Ring of contraction occurs where GI
wall is stretched, pushing bolus forward
• Stimulated by CCK – secreted by
endocrine cells in presence of chyme
Segmentation
• Mixing movement
• Forward and backward movement
that mechanically breaks down food
and mixes it with digestive juices
Large Intestine
 Ileocecal valve: circular, sphincter muscle; prevents food
from returning to ileum (small intestine)
 Cecum: pouch at first portion of the large intestines; lower
end is the appendix
 Colon: absorbs water,
remaining nutrients,
electrolytes; storage of
indigestible materials until
elimination; transport
waste out of the body
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Ascending (right side)
Transverse
Descending (left side)
Sigmoid
Rectum (final 6-8 inches):
storage of feces
Anal Canal
 Anal canal: anus; outlet of
rectum
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Fecal matter: non-digestible
waste products and bacteria
Defecation: emptying of fecal
matter from rectum
 2 Sphincters
 Internal anal sphincter:
involuntary, smooth muscle
 External anal sphincter:
voluntary, skeletal muscle
Accessory Organs
Liver
 Largest gland/solid organ of body;
 Located in the RUQ under
diaphragm; 3 pounds
 Secretes 1 liter of bile /24 hours
 Biliary tree: composed of hepatic
duct, cystic duct, and common bile
duct
Functions
 Manufactures blood proteins (i.e.
antibodies), blood clotting factors
 Stores iron, copper, vitamin
A/D/B12, glycogen
 Produces bile for fat digestion
 Detoxifies blood
Gallbladder
 Pear-shaped muscular sac under the liver
 Stores bile (approx. 500-600 ml. stored)
 Fatty foods enter duodenum 
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stimulates CCK hormone  contracts GB to
release bile  emulsifies fats and stimulates
peristalsis of small intestine muscular tissue
Bile pigments: bilirubin (formed from
breakdown of RBCs)
Bile helps soften stools, thus helping to speed up
the movement of feces in the colon
Bile helps destroy bacteria and other microbes
that can be present in foods
Obstruction of gallbladder  icterus and
jaundice
Cholelithiasis: gallstones = cholesterol and bile
salts
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Caused mainly by dietary choices
Cholecystectomy: removal of GB
Pancreas
 Behind the stomach; head attached to duodenum, tail
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reaching to spleen
Exocrine functions: acini cells secrete digestive juices and
bicarbonate ions (help adjust pH)
Endocrine functions: carbohydrate metabolism
 Insulin and Glucagon: secreted from the islets of
Langerhans for carbohydrate metabolism
Diabetes: decreased secretion
of insulin or insufficient
insulin, therefore glucose
is increased in blood
Pancreatitis: inflammation
caused by overproduction of
pancreatic juices
Appendix
 Function not fully known;
but thought to provide safe
place for good bacteria
 Appendicitis
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inflammation of appendix
not common in elderly
appendectomy – surgical removal of
appendix
Oral Cavity Accessory Organs
Salivary Glands
 Saliva: lubricates food for swallowing; body produces 1500
ml in 24 hours
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Lubricates mouth during speech and chewing
Moistens food for swallowing
Contains enzyme (salivary amylase) which begins chemical breakdown
of complex carbohydrates and starches into sugars
Teeth
 20 primary form 6 months to 2 years
 32 permanent: incisors, canines, premolars/molars,
cuspids/bicuspids
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Mastication: chewing
Bolus: mass of chewed food
Rumble in the Tummy?
 Stomach growling is the result of moving food through
the stomach and into the small intestine.
 Pockets of air and gas also get squeezed into chyme and
create the noises we hear.
 Stomach growling can happen at any time -- not just
when you're hungry -- but if there's food in your
stomach or small intestine, the growling becomes
quieter.
Hungry? Grab a Snickers.
 About two hours after your stomach empties itself, it
begins to produce hormones that stimulate local nerves
to send a message to the brain to prep for more food.
 The brain replies by signaling for the digestive muscles
to restart the process of peristalsis.
 Two results occur:
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First, the contractions sweep up any remaining food that was
missed the first time around.
Second, the vibrations of an empty stomach make you hungry.
Muscle contractions will come and go about every hour, generally
lasting 10 to 20 minutes, until you eat again.
Heartburn, GERD, Acid Reflux, Oh my!
 Heartburn is sometimes used
interchangeably with acid reflux
 Mainly caused by acid splashing up and
out of the stomach.
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Food is a key trigger to heartburn!
Relaxation of esophageal sphincter or over
production of stomach acid
 GERD is usually caused by changes in
the barrier between the stomach and the
esophagus
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Abnormal relaxation of the lower
esophageal sphincter
Impaired expulsion of gastric reflux
from the esophagus
Hiatal Hernia
Crohn’s Disease
 Crohn’s disease belongs to a group of conditions
known as Inflammatory Bowel Diseases (IBD).
 Crohn’s disease is a chronic inflammatory condition of
the gastrointestinal tract.
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Crohn’s most commonly affects the end of the small bowel (the
ileum) and the beginning of the colon
 Symptoms: persistent diarrhea, rectal bleeding,
abdominal cramps and pain, sensation of incomplete
evacuation, constipation (can lead to bowel
obstruction)
Colonoscopy
 Test that allows your doctor to look at the inner lining
of your large intestine (rectum and colon)
 Uses a thin, flexible tube called a colonoscope to look
at the colon
 Helps find ulcers, colon polyps, tumors, and areas of
inflammation or bleeding
Organ
Mechanical Process
Mouth (teeth and tongue)
Mastication
Deglutition
Pharynx
Esophagus
Deglutition
Deglutition
Peristalsis
Churning
Peristalsis
Segmentation
Peristalsis
Segmentation
Peristalsis
Mass peristalsis
Defecation
Stomach
Small Intestine
Ascending and Transverse
Colon
Descending Colon
Rectum