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.

1. GASTRO-INTESTINAL
SYSTEM
BY ROMMEL LUIS C. ISRAEL III
BY ROMMEL LUIS C. ISRAEL III
1

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
2
BY ROMMEL LUIS C. ISRAEL III
2

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
BY ROMMEL LUIS C. ISRAEL III
4

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
BY ROMMEL LUIS C. ISRAEL III
5

6. HUMAN DIGESTIVE SYSTEM
BY ROMMEL LUIS C. ISRAEL III
6

7. Figure 23.2
Food
Ingestion
Propulsion
Esophagus
Stomach
Pharynx
Mechanical
digestion
Chemical
digestion
• Chewing (mouth)
• Churning (stomach)
• Segmentation
(small intestine)
Small
intestine
Large
intestine
Defecation Anus
Feces
Blood
vessel
Lymph
vessel
Absorption
• Swallowing
(oropharynx)
• Peristalsis
(esophagus,
stomach,
small intestine,
large intestine)
Mainly H2O
BY ROMMEL LUIS C. ISRAEL III
7

8. DIGESTION
• Phases
• Ingestion
• Movement
• Digestion
• Absorption
• Further digestion
8
BY ROMMEL LUIS C. ISRAEL III

9. ESOPHAGUS
BY ROMMEL LUIS C. ISRAEL III
9

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
BY ROMMEL LUIS C. ISRAEL III
10

11. . ESOPHAGUS ANATOMY
Drawing illustrates the AJCC divisions (left) and clinical
divisions (right) of the esophagus.
Kim T J et al. Radiographics 2009;29:403-421
©2009 by Radiological Society of North America
BY ROMMEL LUIS C. ISRAEL III
11

12. PERISTALSIS AND
SEGMENTATION
12
BY ROMMEL LUIS C. ISRAEL III

13. STOMACH
BY ROMMEL LUIS C. ISRAEL III
13

14. ANATOMY OF THE STOMACH
14
BY ROMMEL LUIS C. ISRAEL III

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
15
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
BY ROMMEL LUIS C. ISRAEL III
16

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
17
BY ROMMEL LUIS C. ISRAEL III

18. DUODENUM AND RELATED
ORGANS
BY ROMMEL LUIS C. ISRAEL III
18

19. THE DUODENUM AND RELATED
ORGANS
19
BY ROMMEL LUIS C. ISRAEL III

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
BY ROMMEL LUIS C. ISRAEL III
20

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
BY ROMMEL LUIS C. ISRAEL III
21

22. SMALL
INTESTINE
BY ROMMEL LUIS C. ISRAEL III
22

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)
BY ROMMEL LUIS C. ISRAEL III
23

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!
BY ROMMEL LUIS C. ISRAEL III
24

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
BY ROMMEL LUIS C. ISRAEL III
25

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
26
BY ROMMEL LUIS C. ISRAEL III

27. SMALL INTESTINE
• Secretes digestive enzymes
• Peptidases
• Amino-
• Di-
• Tri-
• Sucrases
• Maltase
• Lactase
• Saccharidases
• Di-
• Tri-
• Lipase
• Nucleases
27
BY ROMMEL LUIS C. ISRAEL III

28. LARGE
INTESTINE
BY ROMMEL LUIS C. ISRAEL III
28

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
BY ROMMEL LUIS C. ISRAEL III
29

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
BY ROMMEL LUIS C. ISRAEL III
30

31. LARGE INTESTINE
• Functions
• Mechanical digestion
• Haustral churning
• Peristalsis
• Reflexes
• Gastroileal
• Gastrocolic
• Chemical digestion –
Bacterial digestion
• Ferment
carbohydrates
• Protein/amino acid
breakdown
31
– Absorbs
•More water
•Vitamins
– B
– K
–
Concentrate/eli
minate wastes
BY ROMMEL LUIS C. ISRAEL III

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
32
BY ROMMEL LUIS C. ISRAEL III

33. LIVER
BY ROMMEL LUIS C. ISRAEL III
33

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
BY ROMMEL LUIS C. ISRAEL III
34

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
BY ROMMEL LUIS C. ISRAEL III
35

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
36
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
37
BY ROMMEL LUIS C. ISRAEL III

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
38
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
39
BY ROMMEL LUIS C. ISRAEL III

40. BILIARY TRACT
.
BY ROMMEL LUIS C. ISRAEL III
40

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
BY ROMMEL LUIS C. ISRAEL III
41

42. PANCREAS
BY ROMMEL LUIS C. ISRAEL III
42

43. PANCREAS
• Produces digestive enzymes
• digest proteins
• trypsin, chymotrypsin
• digest starch
• amylase
• digest lipids
• lipase
• Buffers
• neutralizes
acid from
stomach
small
intestine
pancreas
BY ROMMEL LUIS C. ISRAEL III
43

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
BY ROMMEL LUIS C. ISRAEL III
44

45. PANCREATIC ARTERIAL SUPPLY
BY ROMMEL LUIS C. ISRAEL III
45

46. VENOUS DRAINAGE OF THE
PANCREAS
BY ROMMEL LUIS C. ISRAEL III
46

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
BY ROMMEL LUIS C. ISRAEL III
47

48. Figure 23.26a
Small
duct
Acinar cells
Basement
membrane
Zymogen
granules
Rough
endoplasmic
reticulum
(a)p
BY ROMMEL LUIS C. ISRAEL III
48

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
BY ROMMEL LUIS C. ISRAEL III
49

50. PANCREATIC JUICE
• Protease activation in duodenum
• Trypsinogen is activated to trypsin by
brush border enzyme enteropeptidase
• Procarboxypeptidase and
chymotrypsinogen are activated by
trypsin
BY ROMMEL LUIS C. ISRAEL III
50

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
BY ROMMEL LUIS C. ISRAEL III
51

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
BY ROMMEL LUIS C. ISRAEL III
52

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
BY ROMMEL LUIS C. ISRAEL III
53