The Digestive System
Objectives:
• Structure
– Gross Anatomy
– Histology
• Function
– Mechanical
– Chemical
• Development
• Disorders
http://www.youtube.com/watch?v=e3O1A http://www.youtube.com/watch?v=Q25-1
n_Q0qKXzg
dlC8bI
Overview of GI tract Functions
1. Mouth- bite, chew, swallow
(Mastication)
2. Saliva - part of the initial process
of food digestion, enzymes in the
saliva begin break down of starch
and fat
3. Pharynx and esophagus- transport
to…
4. Stomach- mechanical disruption;
absorption of some water &
alcohol
5. Small intestine- chemical &
mechanical digestion & absorption
6. Large intestine- absorb
electrolytes & vitamins (B and K)
7. Rectum and anus- defecation
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Greater Omentum, Mesentery
PURPOSE: Support/organization of
bowels, Fat deposition, Immune
contribution, Infection/wound isolation
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Peritoneum
2 Layers:
1. Parietal peritoneum The outer layer, called, is attached to the
abdominal wall
2. Visceral peritoneum The inner layer, is wrapped around the
internal organs
The term mesentery is often used to refer to a double layer of visceral peritoneum.
There are often blood vessels, nerves, and other structures between these layers.
The space between these two layers is technically outside of the peritoneal sac,
and thus not in the peritoneal cavity.
For our purposes the terms Mesentery
and Peritoneum ought to be viewed as
basically the same thing
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Peritonitis
• Acute inflammation of the peritoneum (the
largest serous membrane in the body)
• Cause
– contamination by infectious microbes during
surgery or from rupture of abdominal organs
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Mouth
Mouths role in digestion :
1. Mastication of food – mechanical break down thru chewing. Mixes
food with saliva
2. Saliva – initial chemical break down of food by enzymes,
lubricates food.
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Pharynx
http://www.youtube.com/watch?v=Fn4pB
_TJhEk&feature=related
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Pharynx
• Funnel-shaped tube of skeletal muscle lined by
mucous membrane
• Deglutition (or swallowing) is facilitated by
saliva and mucus
– starts when bolus is pushed into the top of the
pharynx
– sensory nerves send signals to deglutition center in
brainstem
– úvula and soft palate are lifted to close nasopharynx
– larynx is lifted as epiglottis is bent to cover glottis
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Cleft Palate
Cleft lip and palate are birth defects that affect the upper lip and
the roof of the mouth.
Causes: Genetics, some viruses and toxins
http://www.youtube.com/watch?v=Ehork83SreY
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Esophagus
• Collapsed muscular
tube
• In front of vertebrae
• Posterior to trachea
• Posterior to the heart
• Pierces the diaphragm
at hiatus
– hiatal hernia or
diaphragmatic hernia is
when a piece of the GI tract
pushes through the hiatus
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*Esophagus is posterior to the trachea
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Hernia
http://www.youtube.com/watch?v=d72ezs
Z46gI
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Acid reflux or heart burn occurs when acidic
contents of the stomach flow back up into the
esophagus
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Physiology of the Esophagus - Swallowing
• Voluntary phase---tongue pushes food to back of oral cavity
• Involuntary phase----pharyngeal stage
–
–
–
–
breathing stops & airways are closed
soft palate & uvula are lifted to close off nasopharynx
vocal cords close
epiglottis is bent over airway as larynx is lifted
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Swallowing
• Upper sphincter relaxes
when larynx is lifted
• Peristalsis pushes food
down
• Travel time is 4-8 seconds
for solids and 1 sec for
liquids
• Lower sphincter relaxes as
food approaches
http://www.youtube.com/w
atch?v=jr2CuFRCsP8
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Heimlich Maneuver
For blocked airway
http://www.youtube.com/watch
?v=WleKTUaBCIw
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Anatomy of Stomach
• Which side is it on?
– (Left)
• Size when empty?
– large sausage. Stretches due to rugae (a
series of ridges produced by folding of
the wall of an organ.)
• Parts of stomach
– Cardia, fundus, pylorus, pyloric
sphincter
• The stomach releases proteases (proteindigesting enzymes such as pepsin) and
hydrochloric acid, which kills or inhibits
bacteria and provides the acidic pH for
the proteases to work. Food is churned by
the stomach through muscular contractions
of the wall and converted into chyme
• Empties as small squirts of chyme leave
the stomach through the pyloric valve
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Horse’s have a multi
chambered stomach
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Muscular Structure of Stomach
• Three layers of
smooth muscle-outer longitudinal,
circular & inner
oblique
• Permits greater
churning &
mixing of food
with gastric juice
http://www.youtube.com/watch?v=l4vREUUv9Lw
http://www.youtube.com/watch?v=ig5KI4tswNg
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SIDE EFFECTS OF GASTRIC BY PASS:
Chronic Dehydration
Difficulty swallowing
Gallstones
Hair Loss
Indigestion
Intolerance to certain foods, beverages and drugs
Vomiting
Change in bowel habits
(Diarrhea or loose stools and Constipation)
Kidney stones
Dumping Syndrome
(Combinations of weakness,
dizziness, flushing and warmth,
nausea and palpitation immediately
or shortly after eating )
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Pyloric Stenosis
Belching and projectile vomiting, weight loss, dehydration
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What is a peptic ulcer?
A peptic ulcer is a hole in the gut lining of the stomach, duodenum, or esophagus. An
ulcer occurs when the lining of these organs is corroded by the acidic digestive juices
which are secreted by the stomach cells.
What are the causes of peptic ulcers?
While acid is still considered significant in ulcer formation, the leading cause of ulcer
disease is currently believed to be infection of the stomach by a bacteria
Contrary to popular belief, alcohol, coffee, colas, spicy foods have no proven role in
ulcer formation. Similarly, there is no conclusive evidence to suggest that life stresses or
personality types contribute to ulcer disease.
http://www.yo
utube.com/wa
tch?feature=e
ndscreen&NR
=1&v=KAo6kyoaNk
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Anatomy of the Pancreas
• 5" long by 1" thick
• Main duct joins common bile
duct from liver
• Opens 4" below pyloric
sphincter
• Both an endocrine gland
(producing several important
hormones, including insulin) as
well as an exocrine gland,
secreting pancreatic juice
containing digestive enzymes
that pass to the small intestine.
These enzymes help in the
further breakdown of the
carbohydrates, protein, and
fat in the chyme.
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Pancreatic Cancer
The exact cause is unknown, but
pancreatic cancer is more common
in smokers and people who are
obese.
May often grow without any
symptoms at first. This may mean
pancreatic cancer is more advanced
when it is first found.
Early symptoms of pancreatic cancer
include:
1. Pain or discomfort in the upper
part of the belly or abdomen
2. Loss of appetite and weight loss
3. Jaundice (a yellow color in the
skin, mucus membranes, or the eyes)
4. Dark urine and clay-colored stools
5. Fatigue and weakness
6. Nausea and vomiting
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Liver
1. production of bile, which helps break down fats
in the small intestine – sent directly to small
intestine and also Gallbladder
2. production of certain proteins for blood plasma
3. production of cholesterol to help carry fats
through the body
4. conversion of excess glucose into glycogen
(fat) for storage
5. Storage of iron for hemoglobin (main protein of
blood)
6. conversion of poisonous ammonia to urea
(Urea is one of the end products of protein
metabolism that is excreted in the urine.)
7. clearing the blood of drugs and other poisonous
substances
8. regulating blood clotting
9. removing bacteria from the bloodstream
http://www.youtube.com/watch?v=ZD_Tl
u1JUoI&feature=related
Cirrhosis of the liver
What is cirrhosis?
Cirrhosis is a condition in which the liver slowly deteriorates and malfunctions due to
chronic injury. Scar tissue replaces healthy liver tissue, partially blocking the flow of
blood through the liver. Scarring also impairs the liver’s ability to control infections
remove bacteria and toxins from the blood, process nutrients, hormones, and drugs,
make proteins that regulate blood clotting, produce bile to help absorb fats
A healthy liver is able to regenerate most of its own cells when they become damaged.
With end-stage cirrhosis, the liver can no longer effectively replace damaged cells. A
healthy liver is necessary for survival.
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The Gallbladder
The adult human gallbladder
stores about 50 milliliters of
bile, which is released into the
duodenum when food containing
fat enters the digestive tract.
After being stored in the
gallbladder, the bile becomes
more concentrated than when it
left the liver, increasing its
potency and intensifying its
effect on fats.
http://www.youtube.com/watch?v=ECmw
bwIrBI8
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Gallstones are lumps or stones made up of various crystals that develop
in the gallbladder or bile duct.
When the chemicals in the gallbladder, cholesterol, calcium bilirubinate,
and calcium carbonate are out of balance gallstones may form.
What causes gallstones?
Overweight/obese people, especially women, who have bulging
People who have recently lost lots of weight.
People whose intake of dietary fat is high.
People over 60 years of age.
http://www.youtube.com/watch?v=_gBEh
Xlg4RQ
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Bile Production
• One quart of bile/day is secreted by the liver
– yellow-green in color & pH 7.6 to 8.6
• Components
– water & cholesterol
*Function: aids the process of digestion of
lipids in the small intestine by emulsifying fats in
partly digested food. Also “turns off” HCl and Pepsin so
other digestive enzymes and bacteria can do their job
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$10,000 per Gallbladder on black market
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Anatomy of the Small Intestine
• 20 feet long----1 inch
in diameter
• Large surface area for
majority of absorption
• 3 parts
– duodenum---10 inches
– jejunum---8 feet
– ileum---12 feet
• ends at ileocecal valve
• mesentery and
omentum holds the
small intestine loosely
in place and binds it to
the posterior abdominal
wall
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Mechanical Digestion in the Small Intestine
• Weak peristalsis in
comparison to the
stomach---chyme
remains for 3 to 5
hours
• Segmentation---local
mixing of chyme with
intestinal juices--sloshing back & forth
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Chemical Digestion in the Small Intestine
*Bile from the Liver and/or Gall Bladder flows through the common Bile
Duct joining Pancreatic juice in the Hepatopancreatic duct dumping into
the duodenum where it help further break down chime so that it can be
acted on by intestinal bacteria and absorbed into the blood for transport to
the bodies tissues.
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Absorption of Water
• 9 liters of fluid dumped
into GI tract each day
• Small intestine reabsorbs
8 liters
• Large intestine reabsorbs
90% of that last liter
• Absorption is by osmosis
through cell walls into
vascular capillaries inside
villi
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Anatomy of Large Intestine
•
•
•
•
5 feet long by 2½ inches in diameter
Cecum & appendix at the beginning
Rectum = last 8 inches of GI tract anterior to the sacrum & coccyx
Anal canal = last 1 inch of GI tract
– internal sphincter----smooth muscle & involuntary
– external sphincter----skeletal muscle & voluntary control
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Histology of Large Intestine
•
•
•
•
Muscular layer
– internal circular layer is normal
– outer longitudinal muscle
Appendix
– A finger like vestigial structure.
– Servers a minor role in bacteria
growth and immunity (?)
Bacteria (e.coli) of the large intestine
are responsible for the final stage of
digestion.
Large intestine----absorbs
electrolytes & vitamins (B and K)
Electrolytes are important because they are
what your cells (especially nerve, heart, muscle)
use to maintain voltages across their cell
membranes and to carry electrical impulses
(nerve impulses, muscle contractions) across
*Digestive system normally produces about
themselves and to other cells.
seven liters of gas per day creating 14
occurrences of flatulence per day
25
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Blocked, Impacted, or Twisted
Intestine
Colon Resection:
http://www.youtube.com/watch?v=07xcVl
EoidU
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Appendicitis Attack Symptoms
Pain that intensifies when moving, taking deep breaths, coughing, or
sneezing, Loss of appetite , Nausea, Vomiting, Inability to pass gas, Low
fever that begins after other symptoms , Abdominal swelling, Feeling
like a bowel movement will relieve the discomfort.
http://www.youtube.com/watch?v
=ICI6mT2U6zU
Appendicitis is one of the most common causes of emergency
abdominal surgery in the United States. It usually occurs when the
appendix becomes blocked by feces, a foreign object, or rarely, a
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tumor.
Defecation
Is the final act of digestion by which organisms eliminate
solid, semisolid or liquid waste material (feces) from the
digestive tract via the anus. Waves of muscular
contraction known as peristalsis in the walls of the colon
move fecal matter through the digestive tract towards the
rectum.
http://www.y
outube.com/
watch?v=Xx
vRbxhqoZk
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What are hemorrhoids?
Hemorrhoids are swollen veins in the anal canal. This common problem can
be painful, but it's usually not serious. Change is diet helps, but in extreme
cases surgery can be done.
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Feces are mostly made of
water (about 75%). The rest
is made of dead bacteria
(60% of the dry mass of
feces ), living bacteria,
protein, fiber, cellular linings,
fats, salts, and substances
released from the intestines
(such as mucus) and the liver.
Cat Dissection: GOOD!
http://www.youtube.com/watch?v=KDAC
mSTCAGo
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Cat Dissection: Digestive System
*Find, Isolate, and Remove the following organs:
Salivary glands example
Esophagus - Total length? __________________
Open up the entire esophagus. Is there anything present inside it? __________________________
Identify the hiatus (you may wish to remove the diaphragm.)
Stomach -Total length? __________________
Cardiac Sphincter
Cardiac
Lesser curvature
Greater Curvature
Pyloris
Pyloric sphincter
Open the stomach. Identify the rugae and label them.
*Describe the contents of the stomach:
6. Greater omentum
Mesentery
*What is the purpose of the mesentery?
Small intestine - Total length? __________________
Duodenum
Jejunum
ileum
Iliocecal valve
*Describe the contents of the Small intestine:
9) Large intestine - Total length? __________________
a) Cecum
Do cats have an appendix? Why do you think?
*Describe the contents of the Large intestine:
10) Liver
What is this organs purpose?
11) Gall Bladder
What is this organs purpose?
12) Pancreas (*Note – you do not have to remove this organ as it is diffuse. Simply identify it and pin it.)
What is this organs purpose?
13) Rectum
What is this organs purpose?
14) Anus
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