The document provides an overview of the human gastrointestinal system. It describes the organs that make up the digestive tract, including the mouth, esophagus, stomach, small intestine, large intestine and associated organs like the liver, gallbladder and pancreas. It explains the functions of these organs in digesting, absorbing and eliminating food and waste. Key processes discussed include mechanical and chemical digestion, absorption of nutrients, and role of enzymes and hormones in regulating digestion.
2. DIGESTIVE SYSTEM ORGANIZATION
• Gastrointestinal (Gl) tract
• Tube within a tube
• Direct link/path between organs
• Structures
• Mouth
• Pharynx
• Esophagus
• Stomach
• Small intestine
• Large Intestine
• Rectum
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BY ROMMEL LUIS C. ISRAEL III
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3. MOUTH
• Teeth mechanically
break down food into
small pieces. Tongue
mixes food with saliva
(contains amylase,
which helps break
down starch).
• Epiglottis is a flap-like
structure at the back of
the throat that closes
over the trachea
preventing food from
entering it. It is located
in the Pharynx.
BY ROMMEL LUIS C. ISRAEL III
4. GETTING & USING FOOD
• Ingest
• taking in food
• Digest
• mechanical digestion
• breaking up food into smaller pieces
• chemical digestion
• breaking down food into molecules small
enough to be absorbed into cells
• enzymes
• Absorb
• absorb nutrients across cell membranes
• diffusion
• active transport
• Eliminate
• undigested material passes out of body
intracellular
digestion
extracellular
digestion
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5. DIGESTIVE SYSTEM
• Two groups of organs
1-Alimentary canal (gastrointestinal or GI tract)
Digests and absorbs food
Mouth, pharynx, esophagus, stomach, small intestine, and large
intestine
2-Accessory digestive organs
Teeth, tongue, gallbladder
Digestive glands
Salivary glands
Liver
Pancreas
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10. ESOPHAGUS
• Receives food from pharynx and propels it to
stomach
• Cardia sphincter (lower esophageal sphincter)
controls passage of food from esophagus into
the stomach
• Relaxes = food enters stomach
• Contracts = stomach contents prevented from
reentering the esophagus
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15. STOMACH
• 3 muscle layers
• Oblique
• Circular
• Longitudinal
• Regions
• Cardiac sphincter
• Fundus
• Antrum (pylorus)
• Pyloric sphincter
• Vascular
• Inner surface thrown into
folds – Rugae
• Contains enzymes that work
best at pH 1-2
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BY ROMMEL LUIS C. ISRAEL III
16. STOMACH
• Functions
• disinfect food
• hydrochloric acid = pH 2
• kills bacteria
• food storage
• can stretch to fit
• ~2L food
• digests protein
• pepsin enzyme
But the stomach is made out of protein!
What stops the stomach from digesting itself?
mucus secreted by stomach cells protects stomach
lining
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17. STOMACH
• Functions
• Mix food
• Reservoir
• Start digestion of
• Protein
• Nucleic acids
• Fats
• Activates some enzymes
• Destroy some bacteria
• Makes intrinsic factor – B12
absorption
• Absorbs
• Alcohol
• Water
• Lipophilic acid
• B 12
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20. DUODENUM
•The bile duct and main pancreatic
duct
•Join at the hepatopancreatic
ampulla
• Enter the duodenum at the major
duodenal papilla
• Are controlled by the
hepatopancreatic sphincter
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21. Figure 23.21
Jejunum
Mucosa
with folds
Cystic duct
Duodenum
Hepatopancreatic
ampulla and sphincter
Gallbladder
Right and left
hepatic ducts
of liver
Bile duct and sphincter
Main pancreatic duct
and sphincter
Pancreas
Tail of pancreas
Head of pancreas
Common hepatic duct
Major duodenal
papilla
Accessory pancreatic duct
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23. SMALL INTESTINE: GROSS
ANATOMY
• Major organ of digestion and absorption
• 2–4 m long; from pyloric sphincter to
ileocecal valve
• Subdivisions
1. Duodenum (retroperitoneal)
2. Jejunum (attached posteriorly by
mesentery)
3. Ileum (attached posteriorly by mesentery)
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24. SMALL INTESTINE
• Functions
• digestion
• digest carbohydrates
• amylase from pancreas
• digest proteins
• trypsin & chymotrypsin from pancreas
• digest lipids (fats)
• bile from liver & lipase from pancreas
• absorption
• nutrients move into body cells by:
• diffusion
• active transport
This is
where all the
work is done!
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25. ABSORPTION IN SMALL INTESTINES
• Absorption through villi & microvilli
• finger-like projections
• increases surface area for absorption
SMALL INTESTINES
6 meters long,
but can stretch
to cover a
tennis court
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26. SMALL INTESTINE
• Absorbs
• 80% ingested water
• Electrolytes
• Vitamins
• Minerals
• Carbonates
• Active/facilitated
transport
• Monosaccharides
• Proteins
• Di-/tripeptides
• Amino acids
• Lipids
• Monoglycerides
• Fatty acids
• Micelles
• Chylomicrons
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BY ROMMEL LUIS C. ISRAEL III
27. SMALL INTESTINE
• Secretes digestive enzymes
• Peptidases
• Amino-
• Di-
• Tri-
• Sucrases
• Maltase
• Lactase
• Saccharidases
• Di-
• Tri-
• Lipase
• Nucleases
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BY ROMMEL LUIS C. ISRAEL III
29. Figure 23.29a
Left colic
(splenic) flexure
Transverse
mesocolon
Epiploic
appendages
Descending
colon
Teniae coli
Sigmoid
colon
Cut edge of
mesentery
External anal sphincter
Rectum
Anal canal
(a)
Right colic
(hepatic)
flexure
Transverse
colon
Superior
mesenteric
artery
Haustrum
Ascending
colon
IIeum
IIeocecal
valve
Vermiform appendix
Cecum
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30. LARGE INTESTINES
(COLON)
• Function
• re-absorbs water
• use ~9 liters of water every day in digestive
juices
• if don’t reabsorb water
would die of dehydration
• > 90% of water re-absorbed
• not enough water re-absorbed
• diarrhea
• can be fatal!
• too much water re-absorbed
• constipation
• reabsorb by diffusion
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31. LARGE INTESTINE
• Functions
• Mechanical digestion
• Haustral churning
• Peristalsis
• Reflexes
• Gastroileal
• Gastrocolic
• Chemical digestion –
Bacterial digestion
• Ferment
carbohydrates
• Protein/amino acid
breakdown
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– Absorbs
•More water
•Vitamins
– B
– K
–
Concentrate/eli
minate wastes
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32. FECES FORMATION AND
DEFECATION
• Chyme dehydrated to
form feces
• Feces composition
• Water
• Inorganic salts
• Epithelial cells
• Bacteria
• Byproducts of digestion
• Defecation
• Peristalsis pushes feces
into rectum
• Rectal walls stretch
• Control
• Parasympathetic
• Voluntary
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34. Figure 23.21
Jejunum
Mucosa
with folds
Cystic duct
Duodenum
Hepatopancreatic
ampulla and sphincter
Gallbladder
Right and left
hepatic ducts
of liver
Bile duct and sphincter
Main pancreatic duct
and sphincter
Pancreas
Tail of pancreas
Head of pancreas
Common hepatic duct
Major duodenal
papilla
Accessory pancreatic duct
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35. Figure 23.25c
(c)
Interlobular veins
(to hepatic vein) Central vein
Sinusoids
Portal triad
Plates of
hepatocytes
Portal vein
Fenestrated
lining (endothelial
cells) of sinusoids
Bile duct (receives
bile from bile
canaliculi)
Bile duct
Portal arteriole
Portal venule
Hepatic
macrophages
in sinusoid walls
Bile canaliculi
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36. LIVER
• Location
• R. Hypochondrium
• Epigastric region
• 4 Lobes
• Left
• Quadrate
• Caudate
• Right
• Each lobe has lobules – Contains hepatocytes –
Surround sinusoids – Feed into central vein
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BY ROMMEL LUIS C. ISRAEL III
37. LIVER
• Functions
• Makes bile
• Detergent – emulsifies
fats
• Release promoted by:
• Vagus n.
• CCK
• Secretin
• Contains
• Water
• Bile salts
• Bile pigments
• Electrolytes
• Cholesterol
• Lecithin
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38. LIVER
• Detoxifies/removes
• Drugs
• Alcohol
• Stores
• Gycolgen
• Vitamins (A, D, E, K)
• Fe and other minerals
• Cholesterol
• Activates vitamin D
• Fetal RBC production
• Phagocytosis
• Metabolizes absorbed food
molecules
• Carbohydrates
• Proteins
• Lipids
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BY ROMMEL LUIS C. ISRAEL III
39. LIVER
• Dual blood supply
• Hepatic portal
vein
• Direct input from
small intestine
• Hepatic
artery/vein
• Direct links to
heart
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BY ROMMEL LUIS C. ISRAEL III
41. THE GALLBLADDER
The gallbladder concentrates and stores bile.
Bile:
• Secreted by the liver
• Contains cholesterol, bile pigments and
phospholipids
• Flows from the liver, through the hepatic ducts,
into the gallbladder
• Exits the gallbladder via the cystic duct
• Flows from the cystic duct into the common
bile duct, into the small intestine
• In the small intestine, aids digestion
by breaking down fatty foods and
fat-soluble vitamins
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43. PANCREAS
• Produces digestive enzymes
• digest proteins
• trypsin, chymotrypsin
• digest starch
• amylase
• digest lipids
• lipase
• Buffers
• neutralizes
acid from
stomach
small
intestine
pancreas
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44. PANCREATIC DUCT
• Main duct (Wirsung) runs the entire length of
pancreas
• Joins CBD at the ampulla of Vater
• 2 – 4 mm in diameter, 20 secondary branches
• Ductal pressure is 15 – 30 mm Hg (vs. 7 – 17 in
CBD) thus preventing damage to panc. duct
• Lesser duct (Santorini) drains superior portion of
head and empties separately into 2nd portion of
duodenum
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47. PANCREAS
• Endocrine function
• Pancreatic islets secrete insulin and
glucagon
• Exocrine function
• Acini (clusters of secretory cells) secrete
pancreatic juice
• Zymogen granules of secretory cells
contain digestive enzymes
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49. PANCREATIC JUICE
• Watery alkaline solution (pH 8) neutralizes
chyme
• Electrolytes (primarily HCO3
–)
• Enzymes
• Amylase, lipases, nucleases are secreted in
active form but require ions or bile for
optimal activity
• Proteases secreted in inactive form
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50. PANCREATIC JUICE
• Protease activation in duodenum
• Trypsinogen is activated to trypsin by
brush border enzyme enteropeptidase
• Procarboxypeptidase and
chymotrypsinogen are activated by
trypsin
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51. REGULATION OF BILE SECRETION
•Bile secretion is stimulated by
• Bile salts in enterohepatic
circulation
• Secretin from intestinal cells
exposed to HCl and fatty chyme
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52. REGULATION OF BILE SECRETION
• Gallbladder contraction is stimulated by
• Cholecystokinin (CCK) from intestinal
cells exposed to proteins and fat in
chyme
• Vagal stimulation (minor stimulus)
• Cholecystokinin also causes the
hepatopancreatic sphincter to relax
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53. stomach
kills germs
break up food
digest proteins
store food
mouth
break up food
digest starch
kill germs
moisten food
small intestines
breakdown food
- proteins
- starch
- fats
absorb nutrients
pancreas
produces enzymes to
digest proteins & carbs
liver
produces bile
- stored in gall bladder
break up fats
large intestines
absorb water
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