The digestive system breaks down ingested food into nutrients that can be absorbed and used by the body. It consists of the alimentary canal and accessory organs. The alimentary canal includes the mouth, esophagus, stomach, small intestine, large intestine, and anus. Accessory organs include the teeth, tongue, salivary glands, liver, gallbladder and pancreas. Food is ingested, digested, absorbed, and waste is eliminated in a multi-step process involving both mechanical and chemical breakdown as well as nutrient absorption throughout the alimentary canal.

1. Digestive systemDigestive system
Moath Nairat, MDMoath Nairat, MD

2. Function of the digestive systemFunction of the digestive system
• ingestion: taking food and liquid into
mouth
• Secretion: total about 7 liter into lumen
• Mixing and propulsion: through GI
muscle and peristalsis and motility
• Digestion: Breakdown of ingested food
(mechanical and chemical)
• Absorption: Passage of nutrients into the
blood
• Metabolism: Production of cellular
energy (ATP)
• Defecation: waste substance leave the
GI tract through anus

3. Organs of the Digestive SystemOrgans of the Digestive System
• Two main groups
• Alimentary canal or gastrointestinal tract –
continuous coiled hollow tube from mouth to
anus(5-7 meter)
• Accessory digestive organs: teeth ,tongue
,salivary gland ,liver ,gallbladder ,and
pancreas

4. Organs of the Digestive SystemOrgans of the Digestive System

5. Organs of the Alimentary CanalOrgans of the Alimentary Canal
• Mouth
• Pharynx
• Esophagus
• Stomach
• Small intestine
• Large intestine
• Anus

6. Mouth (Oral Cavity) AnatomyMouth (Oral Cavity) Anatomy
• Lips (labia) – protect
the anterior opening
• Cheeks – form the
lateral walls
• Hard palate – forms
the anterior roof
• Soft palate – forms
the posterior roof
• Uvula – fleshy
projection of the
soft palate

7. Mouth (Oral Cavity) AnatomyMouth (Oral Cavity) Anatomy
• Vestibule – space
between lips
externally and teeth
and gums internally
• Oral cavity – area
contained by the
teeth
• Tongue – attached
at hyoid bone and
styloid processes of
the skull, and by the
lingual frenulum

8. TongueTongue
• Dorsum (upper part of
tongue covered with papillae
taste receptor and buds)
• filiform papillae
• fungiform papillae
• circumvallate papillae
• Paltine tonsil and
lingual tonsil

9. Salivary glands
-Parotid gland: In the parotid fossa, three main
structures transverse this gland – facial nerve,
external carotid artery, and retromandibular
vein. The parotid duct opens near the upper 2nd
molar tooth. The gland is completely serous.
- Submandibular gland: Sitting most
posteriorly in the submandibular triangle, it is
supplied by the facial artery and vein.
Submandibular ducts, which cross the lingual
nerves, open on both sides of the tongue
frenulum. It is mostly serous but partially
mucus,.
- Sublingual gland: The smallest salivary
gland sits beneath the oral mucosa in the floor
of the mouth. It has multiple small openings.
This gland is almost completely mucus-
secreting.

10. Teeth
• Teeth
(mechanical breakdown)
– Incisors used for cutting
– Canines used for stabbing
and holding
– Molars large surface area
used for grinding
• Primary or deciduous
teeth 20
• Secondary or permanent
teeth 32

11. Structure of Teeth
Crown - exposed surface of tooth
Neck - boundary between root and crown
Enamel - outer surface (the hardest substance in the
body 95% calcium salts)
Dentin – bone-like, but noncellular(70% calcium
salts)
Pulp cavity - hollow with blood vessels and nerves
Root canal - canal length of root
gingival sulcus - where gum and tooth meet

12. Processes of the MouthProcesses of the Mouth
• Mastication (chewing) of food
• Mixing masticated food with saliva to
produse easy digestied food called
bolus
• Saliva contain 2 enzyme,salivary
amylase and lingual lipase
• Initiation of swallowing by the tongue
• Allowing for the sense of taste

13. Layers of Alimentary Canal OrgansLayers of Alimentary Canal Organs
• Submucosa
•Just beneath the mucosa
•Soft connective tissue with blood vessels,
nerve endings, and lymphatics also contain
submucosal plexus

14. Layers of Alimentary Canal OrgansLayers of Alimentary Canal Organs
• Mucosa
• Innermost layer
• Moist membrane
1. Surface epithelium : secretion and
absorbtion,renew every 5-7 days also
contain enteroendocrine cells
2. Small amount of connective tissue
(lamina propria): contain blood and
lymphatic vessele also contain MALT
3. Small smooth muscle layer

15. Layers of Alimentary Canal OrgansLayers of Alimentary Canal Organs
• Muscularis externa – smooth muscle
1. Inner circular layer
2. Outer longitudinal layer
Between them is myenteric plexus
• Serosa
• Outermost layer – visceral peritoneum
• Layer of serous fluid-producing cells
(mesothelium)

16. Layers of Alimentary Canal OrgansLayers of Alimentary Canal Organs

17. Digestive Anatomy: Histological

18. Pharynx AnatomyPharynx Anatomy
• Nasopharynx –
not part of the
digestive system
• Oropharynx –
posterior to oral
cavity
• Laryngopharynx –
below the oropharynx
and connected to
the esophagus

19. Pharynx FunctionPharynx Function
• Serves as a passageway for air and
food
• Food is propelled to the esophagus by
two muscle layers
•Longitudinal inner layer
•Circular outer layer
• Food movement is by alternating
contractions of the muscle layers
(peristalsis)

20. EsophagusEsophagus
• Runs from pharynx to stomach through
the diaphragm( 25 cm)
• Conducts food by peristalsis
(slow rhythmic squeezing): contraction
of circular layer above the food and
contraction of longitudinal below the
food
• Passageway for food only (respiratory
system branches off after the pharynx)

21. Esophagus
- The esophagus is posterior to the larynx
and trachea in the neck region and upper
thorax. It travels on the right side of the
descending aorta, passes through the
diaphragm, and connects with the
stomach.
-There are also inner circular and outer
longitudinal muscle layers.
- The upper third is skeletal muscle
(voluntary), middle third is mixed, and lower
third is smooth muscle (involuntary).
-esophagogastric junction is located
approximately at the level of the diaphragm.
Contractions of the diaphragm create sphincter-
like effects, preventing reflux of stomach acids
and content. The esophagogastric junction is a
functional, not anatomical, sphincter.

22. Peristalsis in Esophagus
Bolus of
food
Muscles relax,
allowing
passageway
to open
Stomach
Muscles
contract,
constricting
passageway
and pushing
bolus down
Muscles
relax
Muscles contract
Muscles relax
Muscles contract

23. Stomach AnatomyStomach Anatomy
• Located on the left side of the
abdominal cavity
• Food enters at the
cardioesophageal sphincter
Site where food is churned into chyme
Protein digestion begins

24. Stomach AnatomyStomach Anatomy
• Regions of the stomach
•Cardiac region – near the heart
•Fundus
•Body
•Phylorus – funnel-shaped terminal end
• Food empties into the small intestine at
the pyloric sphincter

25. Stomach

26. Stomach AnatomyStomach Anatomy
• Rugae – internal folds of the mucosa
• External regions
•Lesser curvature
•Greater curvature

27. Stomach

28. Stomach AnatomyStomach Anatomy
• Layers of peritoneum attached to the
stomach
•Lesser omentum – attaches the liver to the
lesser curvature
•Greater omentum – attaches the greater
curvature to the transverse colon which
Contains fat to insulate, cushion, and
protect abdominal organs

29. Stomach AnatomyStomach Anatomy

31. Stomach FunctionsStomach Functions
• Acts as a storage tank for food
• Site of food breakdown and mixing
• Chemical breakdown of protein begins
• Delivers chyme (processed food) to the
small intestine

32. Specialized Mucosa of theSpecialized Mucosa of the
StomachStomach
• Simple columnar epithelium
• Mucous neck cells – produce a sticky
alkaline mucus
• Gastric glands – secrete gastric juice
• Chief cells – produce protein-digesting
enzymes (pepsinogens)
• Parietal cells – produce hydrochloric acid
and Intrinsic factor(B12 absorption)
• Endocrine cells (G cell) – produce gastrin
which stimulates both parietal and chief cells)

33. Structure of the Stomach MucosaStructure of the Stomach Mucosa
• Gastric pits
formed by
folded mucosa
• Glands and
specialized
cells are in the
gastric gland
region

34. Structure of the Stomach MucosaStructure of the Stomach Mucosa

35. Peritoneum
• Is the largest serous membrane of the body consist of
mesothelium
• Divide into
1. Parietal peritoneum: lines the wall of abdominopelvic
cavity internally
2. Visceral peritoneum: cover some oh the organs in the
cavity
3. The space between them contain fluid and called
peritoneal cavity this cavity may be accumulated by
several liters of fluid state called ascites

36. MembranesMembranes
Mesenteries - double sheets of peritoneum, surrounding and
suspending portions of the digestive
organs
Peritoneal folds
1. falciform ligament:- attach the liver to anterior abdominal
wall and diaphragm
2. Greater omentum - "fatty apron", hangs anteriorly from
stomach, double layer encloses fat
3. Lesser omentum - between stomach and liver
4. Mesentery proper - suspends and wraps the small intestine
5. Mesocolon - suspends and wraps the colon, parts are
i. transverse mesocolon
ii. sigmoid mesocolon
• Ascending and descending ,pancreas, first 2 parts of the
duodenum and kidneys are Retroperitoneal structure

37. peritoneum

38. Mesenteries
• Greater omentum
and transverse colon
reflected

39. Mesenteries
• Superficial view
of the abdominal
organs

40. Small IntestineSmall Intestine
• The body’s major digestive organ
• Site of nutrient absorption into the blood
• Muscular tube extending form the
pyloric sphincter to the ileocecal valve
• Suspended from the posterior
abdominal wall by the mesentery

41. Subdivisions of the Small IntestineSubdivisions of the Small Intestine
• Duodenum(25cm)
•Attached to the stomach
•Curves around the head of the pancreas
•Fixed retroperitoneal structure
• Jejunum (2.5m)
•Attaches anteriorly to the duodenum
• Ileum (3.5m)
•Extends from jejunum to large intestine

42. RegionsRegions of Small Intestineof Small Intestine

43. Small intestine

44. Duodenum and Related Organs
Liver
Bile
Gall-
bladder
Bile
Duodenum of
small intestine
Acid chyme
Pancreatic
juice
Intestinal enzymes
Stomach
Pancreas

45. Chemical Digestion in the SmallChemical Digestion in the Small
IntestineIntestine
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• Source of enzymes that are mixed with
chyme
•Intestinal cells
•Pancreas
• Bile enters from the gall bladder

46. Villi of the Small IntestineVilli of the Small Intestine
SlideCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Fingerlike
structures formed
by the mucosa
• Give the small
intestine more
surface area
Figure 14.7a

47. Microvilli of the Small IntestineMicrovilli of the Small Intestine
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• Small projections of the
plasma membrane
• Found on absorptive cells
Figure 14.7c

48. Structures Involved in AbsorptionStructures Involved in Absorption
of Nutrientsof Nutrients
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• Absorptive cells
• Blood capillaries
• Lacteals (specialized
lymphatic capillaries)
Figure 14.7b

49. Folds of the Small IntestineFolds of the Small Intestine
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• Called circular folds or plicae circulares
• Deep folds of the mucosa and
submucosa
• Do not disappear when filled with food
• The submucosa has Peyer’s patches
(collections of lymphatic tissue)

50. Digestion in the Small IntestineDigestion in the Small Intestine
SlideCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Enzymes from the brush border
•Break double sugars into simple sugars
•Complete some protein digestion
• Pancreatic enzymes play the major
digestive function
•Help complete digestion of starch
(pancreatic amylase)
•Carry out about half of all protein digestion
(trypsin, etc.)

51. Chemical Digestion in the SmallChemical Digestion in the Small
IntestineIntestine
SlideCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 14.6

52. Digestion in the Small IntestineDigestion in the Small Intestine
SlideCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Pancreatic enzymes play the major
digestive function (continued)
•Responsible for fat digestion (lipase)
•Digest nucleic acids (nucleases)
•Alkaline content neutralizes acidic chyme

53. Absorption in the Small IntestineAbsorption in the Small Intestine
SlideCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Water is absorbed along the length of
the small intestine
• End products of digestion
•Most substances are absorbed by active
transport through cell membranes
•Lipids are absorbed by diffusion
• Substances are transported to the liver
by the hepatic portal vein or lymph

54. Propulsion in the Small IntestinePropulsion in the Small Intestine
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• Peristalsis is the major means of
moving food
• Segmental movements
•Mix chyme with digestive juices
•Aid in propelling food

55. Digestive Secretions:
(≈7 L / Day From Tissues into
Lumen)• Salivary glands
• Pancreas
• Water
• Enzymes
• Mucus
• Ions: H+
, K+
, Na+
• HCO3
-
, Cl-
• Mass Balance (H2O)

56. Large IntestineLarge Intestine
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• Larger in diameter, but shorter than the
small intestine
• Frames the internal abdomen

57. Large IntestineLarge Intestine
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Figure 14.8

58. CecumCecum –– pocket at proximal end with
Appendix
ColonColon
Ascending colon - on right, between
cecum and right colic flexure
Transverse colon - horizontal portion
Descending colon - left side, between
left colic flexure and
Sigmoid colon - S bend near terminal
end
Regions of Large IntestineRegions of Large Intestine
RectumRectum –– terminal end is anal canal - ending at the anus -
which has internal involuntary sphincter and external voluntary
sphincter

59. 1. Mucosa - abundant goblet cells, stratified
squamous epithelium near anal canal
2. No villi
3. Longitudinal muscle layer incomplete, forms
three bands or taenia coli
4. Circular muscle - forms pockets or haustra
between bands
Histology of Large IntestineHistology of Large Intestine

60. Functions of the Large IntestineFunctions of the Large Intestine
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• Absorption of water
• Eliminates indigestible food from the
body as feces
• Does not participate in digestion of food
• Goblet cells produce mucus to act as a
lubricant

61. Structures of the Large IntestineStructures of the Large Intestine
SlideCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Cecum – saclike first part of the large
intestine
• Appendix
•Accumulation of lymphatic tissue that
sometimes becomes inflamed
(appendicitis)
•Hangs from the cecum

62. Structures of the Large IntestineStructures of the Large Intestine
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• Colon
•Ascending
•Transverse
•Descending
•S-shaped sigmoidal
• Rectum
• Anus – external body opening

63. Food Breakdown and Absorption inFood Breakdown and Absorption in
the Large Intestinethe Large Intestine
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• No digestive enzymes are produced
• Resident bacteria digest remaining
nutrients
•Produce some vitamin K and B
•Release gases
• Water and vitamins K and B are absorbed
• Remaining materials are eliminated via
feces

64. Propulsion in the Large IntestinePropulsion in the Large Intestine
SlideCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Sluggish peristalsis
• Mass movements
•Slow, powerful movements
•Occur three to four times per day
• Presence of feces in the rectum causes
a defecation reflex
•Internal anal sphincter is relaxed
•Defecation occurs with relaxation of the
voluntary (external) anal sphincter

65. SalivaSaliva
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• Mixture of mucus and serous fluids
• Helps to form a food bolus
• Contains salivary amylase to begin
starch digestion
• Dissolves chemicals so they can be
tasted

66. Chemistry of Digestion:
Carbohydrates

67. Enzymes in Small Intestine

68. PancreasPancreas
Slide
• Produces a wide spectrum of digestive
enzymes that break down all categories of food
• Enzymes are secreted into the duodenum
• Alkaline fluid introduced with enzymes
neutralizes acidic chyme
• Endocrine products of pancreas (langerhans
island)
•Insulin
•Glucagons
•Somatostatin

69. Exocrine Pancreas: Histology

71. Composition and Function of
Pancreatic Juice
• Examples include
• Trypsinogen is activated to trypsin
• Procarboxypeptidase is activated to
carboxypeptidase
• Active enzymes secreted
• Amylase, lipases, and nucleases
• These enzymes require ions or bile for
optimal activity

72. • Retroperitoneal :compose
of head, body and tail
• Endocrine and exocrine
gland
• Common bile duct and
major pancreatic duct lead
to ampulla of vater then to
second part of duodenum
through sphincter of oddi
PancreasPancreas

73. LiverLiver
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• Largest gland in the body
• Located on the right side of the body
under the diaphragm
• Consists of four lobes suspended from
the diaphragm and abdominal wall by
the falciform ligament
• Connected to the gall bladder via the
common hepatic duct

74. Liver
On right under diaphragm,
largest organ made up of 4
lobes (left and right, caudate,
and quadrate)
Hilus (porta hepatis) –
underside "entry" point
Gall bladder
Microscopic anatomy: Liver lobules and triads

75. Microscopic Anatomy of
Liver

76. Visceral Surface of the Liver

77. Role of the Liver in MetabolismRole of the Liver in Metabolism
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• Several roles in digestion
• Detoxifies drugs and alcohol
• Degrades hormones
• Produce cholesterol, blood proteins
(albumin and clotting proteins)
• Plays a central role in metabolism

78. BileBile
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• Produced by cells in the liver
• Composition
•Bile salts
•Bile pigment (mostly bilirubin from the
breakdown of hemoglobin)
•Cholesterol
•Phospholipids
•Electrolytes

79. Gall BladderGall Bladder
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• Sac found in hollow fossa of liver
• Stores bile from the liver by way of the
cystic duct
• Bile is introduced into the duodenum in
the presence of fatty food
• Gallstones can cause blockages

80. Chemical Digestion in the SmallChemical Digestion in the Small
IntestineIntestine
SlideCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 14.6

81. Gallbladder
• Stores and concentrates bile to ten folds
• Expels bile into duodenum
– Bile emulsifies fats

82. Processes of the Digestive SystemProcesses of the Digestive System
SlideCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Ingestion – getting food into the mouth
• Propulsion – moving foods from one
region of the digestive system to
another

83. Processes of the Digestive SystemProcesses of the Digestive System
SlideCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
•Peristalsis – alternating
waves of contraction
•Segmentation – moving
materials back and forth
to aid in mixing
Figure 14.12

84. Processes of the Digestive SystemProcesses of the Digestive System
SlideCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Mechanical digestion
•Mixing of food in the mouth by the tongue
•Churning of food in the stomach
•Segmentation in the small intestine

85. Processes of the Digestive SystemProcesses of the Digestive System
SlideCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Chemical Digestion
•Enzymes break down food molecules into
their building blocks
•Each major food group uses different
enzymes
•Carbohydrates are broken to simple sugars
•Proteins are broken to amino acids
•Fats are broken to fatty acids and alcohols

86. Processes of the Digestive SystemProcesses of the Digestive System
SlideCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Absorption
•End products of digestion are absorbed in
the blood or lymph
•Food must enter mucosal cells and then
into blood or lymph capillaries
• Defecation
•Elimination of indigestible substances as
feces

87. Processes of the Digestive SystemProcesses of the Digestive System
Slide

88. Control of Digestive ActivityControl of Digestive Activity
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• Mostly controlled by reflexes via the
parasympathetic division
• Chemical and mechanical receptors are
located in organ walls that trigger
reflexes

89. NutritionNutrition
Slide
• Nutrient – substance used by the
body for growth, maintenance, and
repair
• Categories of nutrients
•Carbohydrates: simple sugars, starches,
fiber
•Lipids: triglycerides, phospholipids, fatty
acids
•Proteins: amino acids
•Vitamins
•Mineral
•Water