The Digestive System

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Transcript The Digestive System

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 non-digestible substances
produced during metabolism
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
Four Layers of the Alimentary
Canal
 Mucosa layer:
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Formed by epithelium and some connective tissue, comes into direct
contact with food passing through the canal; secretes mucus that
protects and lubricates the lining
 Submucosa layer:
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Composed of loose connective tissue, blood vessels, and many nerve
endings; blood vessels carry away the nutrients that are absorbed, and
the nerve endings stimulate the muscle fibers so that the food is
continually moving by peristalsis
 Muscular layer:
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Consists of a circular and longitudinal band of visceral muscles; is the
thickest of the four layers. Main function: peristalsis
 Serous layer:
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Continuous with the mesentery, the connective tissues that attach to the
posterior body wall and hold the digestive organs in their proper
position
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
Oral Cavity
 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/Esophagus
Passageways approximately 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 peristalsis
Stomach
 Food stays 3-4 hours for
physical and chemical
breakdown
 Stomach is located in the Left
Upper Quadrant (LUQ) of
abdomen
 4 layers (much like AC)
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Mucosa
Submucosa
Muscular (3 layers of muscle)
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Oblique, circular, longitudinal
Serous
 3 parts: Fundus, body, antrum
 Rugae (gastric folds): folds in stomach to
increase surface area
 Stomach acid: hydrochloric acid,
potassium chloride, and sodium chloride
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Key role in digestion and denaturing of enzymes
Gastric acid is produced by cells in the lining of
the stomach
Other cells in the stomach produce bicarbonate
to buffer the fluid, ensuring that it does not
become too acidic.
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These cells also produce mucus which forms a
viscous physical barrier to prevent gastric acid
from damaging the stomach
 Gastric enzymes: pepsin (protein), rennin,
lipase (fats), HCl (kills bacteria, helps in
absorption of Fe, activates pepsin)
 Chyme: gastric juices plus digested food
Stomach
(ctd.)
Stomach Sphincters
 Sphincters: prevent reflux
 Cardiac (gastroesophageal):
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 3-4 hours so that
digestion can occur
Protective
Linings
 Peritoneum: silk-like
membrane that lines your
inner abdominal wall and
covers the organs within your
abdomen, decreases friction of
organs
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Inflammation from bacterial or
fungal infection: peritonitis
 Mesentery: greater and lesser
omentum forms protective
covering that insulates organs
and holds them in place
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
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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.
Jejunum and
Ileum
The Digestive
System
A D VA N C E D H U M A N A N AT O M Y – DAY 2 … S O R T O F
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
HOLD UP
 Let’s talk about CCK
 Cholecystokinin is secreted by cells of the upper small
intestine. Its secretion is stimulated by the introduction of
hydrochloric acid, amino acids, or fatty acids into
the stomach or duodenum.
 Just mentioned  Cholecystokinin stimulates
the gallbladder to contract and release stored bile into the
intestine.
 It also stimulates the secretion of pancreatic juice and may
induce satiety.
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Meal-induced secretion of cholecystokinin activates the satiety centre of
the hypothalamus in the brain so that the person feels full and stops
eating.
Because cholecystokinin inhibits emptying of the stomach, the sensation
of satiety may be the result of distension of the stomach.
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
 Sits at the junction of the
small intestine and large
intestine.
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About 4 inches long.
Sits in the lower right abdomen.
 Function not fully known; but
thought to provide safe place
for good bacteria
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Reboots digestive system after
diarrheal illnesses
 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 – stomach pushes through
diaphragm
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 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)
 Treatments: immunosuppressants, steroids, corrective
surgery, diet
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
Mouth (teeth and
tongue)
Pharynx
Deglutition
Mastication
Peristalsis
Churning
Defecation
Segmentation
Esophagus
Stomach
Small Intestine
Ascending and
Transverse Colon
Descending Colon
Rectum
Mechanical Process
Mastication
Deglutition
Deglutition
Deglutition
Peristalsis
Churning
Peristalsis
Segmentation
Peristalsis
Segmentation
Peristalsis
Peristalsis
Defecation
Article Questions
 Answer the following questions on the back of the
article!
1.
2.
3.
4.
5.
What is the role of the Paneth cell in your digestive system?
What types of things can occur when the Paneth cells activity is
weak or non-existant?
What does IBD do to a person’s digestive system?
Explain Nan Gao’s role in the research of this particular type of
cell.
What type of benefits could come of Gao and Yap’s research in
this particular field?