The Digestive System & Body Metabolism
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The Alimentary Canal
(or gastrointestinal, GI,
tract) is the hollow tube
where digestion occurs.
The organs include:
mouth, pharynx,
esophagus, stomach,
small intestine, large
intestine, and anus.
It is ~30 feet long.
http://www.google.com/imgres
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Digestion is the decomposition (breakdown)
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This is both chemical and mechanical.
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Mastication: chewing food.
of food for the body’s use.
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Digestion begins here.
Food is broken
down mechanically
and chemically.
Its accessory
organs:
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Cheeks
Lips
Tongue
Palate
Teeth
Mouth (Oral Cavity):
http://www.blogaholics.ca/wp/uploads/illu_mouth.jpg
Swallowing occurs in 3 stages:
◦ Voluntary: food is chewed & consciously swallowed
◦ Swallowing reflex is triggered: through a variety of
steps, food is moved by peristalsis to the esophagus
◦ Peristalsis: food moves through the esophagus
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While swallowing, breathing does not occur.
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From the stomach,
food passes thru to the
pharynx.
It contains 3 parts:
◦ Nasopharynx (air
passageway)
◦ Oropharynx (food
passageway)
◦ Laryngopharynx
(passageway to the
esophagus)
Pharynx:
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A tube that runs ~25cm
(10”) long
Allows peristalsis to
continue
Just before the esophagus
meets the stomach is a
circular section of smooth
muscle called the cardiac
sphincter (a.k.a. lower
esophageal sphincter)
which controls the
movement of food into
the stomach. Usually this
sphincter is closed (until
food reaches it).
Esophagus:
◦ Mucosa (mucous membrane): contains
glands that secrete mucus & digestive
enzymes
 serves as protection (underlying tissues)
◦ Submucosa
◦ Muscular layer: smooth muscle and some
nerves
 function is movement.
◦ Serosa (serous layer)
Four Layers:
http://www.webbooks.com/elibrary/medicine/Physiology/Digestive/stomach.jpg
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J-shaped organ that
is below the cardiac
sphincter of the
esophagus
It can hold ~1 liter
or more
It contains mucosal
and submucosal
layers
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Mixes food with
gastric juices (that
contain enzymes &
acids)
http://mywebpages.comcast.net/wnor/stomachinside.jpg
http://www.nfl.com/gamecenter?game_id=29294&displayPage=tab_gamecenter&season=2007&week=REG7
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Function: Finish digestion and begin absorption
of digested particles
Parts of the Small Intestine:
◦ Duodenum: first portion; ~25cm long
◦ Jejunum: second section
◦ Ileum: last section (not truly distinctive from the
jejunum)
Both the jejunum and the ileum are protected by the
peritoneal membrane called the mesentery
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Intestinal villi are tiny projections that come
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The small intestine is the most important
from the small intestines that increase the
surface area and aid in absorption.
absorbing organ of the alimentary canal.
Small Intestine:
http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/1922
1.jpg
http://www.google.com/imgres
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Chyme moves from the small intestine into the
large intestine
Much shorter than the small intestine but is
larger in its diameter
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“surrounds” the small intestine
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absorbs water & electrolytes from chyme
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the remaining material becomes feces.
◦ This is ~75% water while the remaining is anything
that was not digested or absorbed (electrolytes,
mucus, intestinal cells, bacteria & bile pigments which
give feces its color).
◦ Its odor comes from bacteria products.
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Does not contain villi
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Parts of the Large Intestine:
◦ Cecum: 1st part of the large intestine which is
directly below the ileocecal sphincter.
 Below this is the vermiform appendix (a.k.a. appendix).
This has no known function but has been discovered to
have some lymphatic tissue.
◦ Colon: has 4 portions:
 Ascending colon: upward
 Transverse colon: below the stomach; largest section
 Descending colon: downward
 Sigmoid colon: twists into an S-shape, becoming this;
the sigmoid reaches the rectum.
◦ Rectum: ends at ~5cm below the tip of the coccyx
◦ Anal Canal: an opening to the external
environment; feces exits the body.
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The anus is guarded by 2 sphincters:
◦ The internal anal sphincter muscle: involuntary
control (smooth muscle)
◦ External anal sphincter muscle: voluntary control
(skeletal muscle)
Large Intestine:
http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/1922
0.jpg
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Function: masticate
Primary teeth (a.k.a.
deciduous teeth) are the
first set of teeth
◦ 20 teeth (10 in each jaw)
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http://www.cdha.ca/images/facts_baby_6.gif
Secondary teeth (a.k.a.
permanent teeth) are the
second set of teeth
◦ 32 teeth (16 in each jaw)
◦ grow in at 6-25 years (3rd
molars appear between 1725)
http://www.tela.co.in/images/permteeth.jpg
 incisors (front teeth) have sharp edges
to bite off food
 cuspids (eye teeth) are sharp,
sometimes pointed for biting, grabbing
& tearing food
 biscuspids (behind cuspids) and molars
(back teeth) are flat for grinding food
Crown (above the gum)
Root (below the gum; anchors)
Enamel (glossy white covering
composed of calcium)
Dentin (bone-like substance that
surrounds the tooth’s interior
pulp cavity)
Pulp cavity (interior tooth
composed of BVs, nerves &
connective tissue)
Root canal (BVs and nerves that
run the center of the pulp
cavity)
http://apps.uwhealth.org/health/adam/graphics/images/en/1121.jpg
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http://cache.eb.com/eb/image?id=74321&rendTypeId=4
secrete saliva
(contains serous fluid
& mucus)
Serous fluid contains
a digestive enzyme,
amylase which breaks
down sugars.
Mucus lubricates &
coats the food
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Endocrine AND an
exocrine gland.
Produces pancreatic
juice.
Pancreatic juice
digests carbs, fats,
nucleic acids and
proteins.
http://www.med.umich.edu/1libr/wha/pancreas.gif
Liver:
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Gallbladder:
Reddish-brown
2 lobes
Produces bile (which
emulsifies fat)
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Connected to liver &
small intestine
Stores bile
http://www.pbiv.com/images/nature/lbp/liver_diagram.gif
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Ingestion: to eat
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Propulsion: to move food throughout the canal
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Mechanical digestion: to chew, churn; physical
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(peristalsis)
break down
Chemical digestion: to breakdown food with
enzymes
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Absorption: to transport products of digestion
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Defection: to eliminate waste
into blood stream
Know the location and final product of each
macromolecule digestion:
..\..\..\..\A&P_files\macromolecule end product of
digestion chart.docx
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http://www.buzzle.com/articles/list-of-digestiveenzymes.html
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Polysaccharides (mostly starch) are broken down
into disaccharides and monosaccharides (sugars.)
Proteins are broken down into amino acids.
Fats are broken down into glycerol and fatty acids.
Nucleic acids are broken down into nucleotides.
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Chyme takes 3-10 hours to move through
the small intestine
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A peristaltic rush can occur if the small
intestine is irritated.
◦ This is a sweeping motion that empties
the small intestine’s contents into the
large intestines and continues that
sweeping motion without nutrient
absorption.
◦ Diarrhea may result.
Movements of large intestine: both mixing
and peristalsis:
 Slower than the small intestine
 Peristalsis occurs 2-3 times daily
 Peristaltic waves produce mass
movements (irritation & inflammation,
such as colitis, also stimulate these mass
movements)
◦ Defecation reflex is the force of pushing
feces out the anus
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Look up online or in text!
Know the following:
appendicitis, gallstones, jaundice, hepatitis,
cirrhosis, heartburn, hiatal hernia, vomiting,
pancreatitis, peptic ulcers, diverticulosis,
diarrhea, constipation, BMR, hyperthyroidism,
hypothyroidism, hypothermia, frostbite,
hyperthermia, heat stroke, heat exhaustion, &
appendicitis