Exercise 41
Digestive System
1
Digestion and absorption
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It is the physical and chemical break
down of food
Absorption
 It is the passing of the digested food
through the epithelial cells into the
blood stream
Digestive system
3
Gastrointestinal tract
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4
It is the alimentary canal
Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large instestine
Accessory digestive organs
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Salivary glands
Gallbladder
Liver
Pancreas
Teeth
General histology of the
gastrointestinal tract
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6
It has 4 tunics
 Mucosa
• Epithelium – simple columnar
• Lamina propria – areolar tissue
• Muscularis mucosa
• Smooth muscle that enables
movement of the mucosa
General histology of the
gastrointestinal tract
7
• Functions of the mucosa are
secretion, absorption, protection
 Submucosa
• Dense connective tissue
• Blood vessels
• Lymph nodes and vessels
• Submucosal plexus
• Functions are nutrition and
protection of the mucosa
General histology of the
gastrointestinal tract
 Muscularis
externa
• Inner circular layer of smooth
muscle
• Outer longitudinal layer of smooth
muscle
• Myenteric plexus
• Allows GI movements
8
General histology of the
gastrointestinal tract
 Serosa
9
(abdominal organs)
• Most outer layer
• Mesothelium – areolar tissue
• Functions is to reduce friction
between GI organs
 Adventitia
• Coarse fibrous tissue that binds
the GI organs to the surrounding
tissues. Anchors and protects
them
Oral cavity
10
Macroscopy of the digestive
tract
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Oral cavity or mouth
 Oral cavity
 Lips or labia
• Superior and inferior labial frenulum
 Cheeks
 Palate
• Soft with uvula
• Hard
• Palatine raphe
11
Macroscopy of the digestive
tract
 Tongue
• Lingual frenulum
 Vestibule
 Palatine tonsil
• Palatoglossal arch
• Palatopharyngeal arch
12
Macroscopy of the digestive
tract
 Lingual
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tonsil
 Salivary glands
• Saliva
• Salivary amylase
Pharynx
 Nasopharynx
 Oropharynx
 Laryngopharynx
Macroscopy of the digestive
tract
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14
Esophagus
 Peristalsis
 Gastroesophageal sphincter
 Adventitia and not serosa
Stomach
 Cardiac region
 Fundus
 Body
Macroscopy of the digestive
tract
 Pyloric
region
• Pyloric sphincter
 Greater curvature
 Greater omentum
• From the greater curvature down
to the abdominal organs
 Lesser curvature
15
Macroscopy of the digestive
tract
 Lesser
omentum
 From the lesser curvature to the liver
 Gastric pit
 Gastric rugae
 Function of the stomach is to
process the food forming the chyme
16
Histology of the stomach
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Histology of the stomach
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Mucosa
 Gastric glands
• Chief or zymogenic cells:
• Located on the fundus
• Produce pepsinogen
Histology of the stomach
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• Parietal cells:
• Located on the fundus
• Produce HCL
• Produce intrinsic factor
Enteroendocrine cells:
• Located on the pyloric region
• Release hormones
Submucosa
Histology of the stomach
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Muscularis externa
 Oblique layer
 Circular layer
 Longitudinal layer
Gastroesphageal junction
(Cardioesophageal)
 Stratified squamous epithelium on
the esophagus
 Simple columnar on the stomach
Small intestine
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From the pyloric sphincter to the
ileocecal valve
Mesentery Proper
• Double layer of peritoneum that
attaches the small intestine to the
posterior body wall
Small intestine
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22
Plicae
 Deep folds of the mucosa and
submucosa
 They cause the chyme to spiral
through the intestine slowing and
mixing it
Intestinal crypts of crypts of Lieberkuhn
 It is the invaginated area of the
mucosa between the villi
Small intestine
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Lacteal
 It is the lymphatic capillary present in
each villus
Function of the small intestine
 Nutrients absorption
PART B
24
Subdivisions of the small
intestine
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Small intestine
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Duodenum
 Pancreatic duct
 Bile duct
 Hepatopancreatic ampulla
 Major duodenal papilla
 Hepatopancreatic sphincter or
sphincter of Oddi
 Duodenal glands or Brunner’s glands
– located in the submucosal layer
Small intestine
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Jejunum
 Where the food is most absorbed
Ileum
 Ileocecal valve
 Peyer’s patches
• Aggregation of lymphoid tissue
more prominent in the ileum
Small intestine
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Superficial structures of the small
intestine that increases the absorptive
area of the mucosa
 Villi
• Fingerlike projections of the
mucosa
Small intestine
 Microvilli
or brush border
• Projections of the cell membrane
of the columnar epithelium
• Brush border enzymes
 Plicae
29
Histology of the small
intestine
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30
Identify these structures on the slide:
 Plica
 Cripts
 Villi
 Brush border
 Layers of the intestine
Histology of the small
intestine
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Duodenum
 Submucosa with Brunner’s glands
Jejunum
 Longest, leafy villi
Ileum
 Submucosa with Peyer’s patches
The large intestine
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Large intestine
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From the ileocecal valve to the anus
Mesocolon
 Attaches the large intestine to the
body wall
Cecum
 It is the first part
Appendix
 A blind tube like structure connected
to the cecum
Large intestine
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Colon:
Ascending
 Right side of the abdominal cavity
 Right colic (hepatic) flexure
 It is retroperitoneal
Transverse
 Cross the abdominal cavity
 Left colic (splenic) flexure
Large intestine
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Descending
 It is retroperitoneal
Sigmoid
 S-shaped
 Located in the pelvis
Rectum
Large intestine
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Anus
 External sphincter - skeletal muscle
• Voluntary
 Internal sphincter – smooth muscle
• involuntary
Large intestine - structures
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Tenia coli
 It is the longitudinal muscle layer of
muscularis externa
 It is in the shape of a muscle band
Haustra
 Pocket like sacs of the large intestine
 It is caused by the tenia coli
Large intestine - structures
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Epiploic appendages
 Fat-filled pouches of visceral
peritoneum hanging for the colon’s
surface
Large intestine
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Functions of the large intestine
 Consolidate and propel the fecal
matter to the anus
 Site for intestinal bacteria to
synthesize vitamins B and K
 Site for water absorption
Histology of the large
intestine
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Lumen
Crypts
Layers of the digestive tract
Mucosa with the maximum amount of
goblet cells
No villi
Accessory digestive organs
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Teeth:
 Deciduous (milk teeth)
• They appear between 6 month
and 2 ½ years of age
• They begin to shed at 6 years of
age
• They are completely shed by the
age of 12
Accessory digestive organs
 Permanent
• They begin to appear at 6 years of
age
• They last for a lifetime
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Types of teeth
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Accessory digestive organs
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Classification of the teeth
 Incisors
• Chisel shaped
• Shearing action when biting
• 4 superiors and 4 inferiors (2
centrals and 2 laterals)
• Single-rooted
Accessory digestive organs
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Canines
 Cone-shaped
 It tears the food
 2 superiors and 2 inferiors
 Single-rooted
Accessory digestive organs
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Premolars
 Two cusps
 It grinds the food
 4 superiors and 4 inferiors
• 2 first premolars
• 2 second premolars
 Generally single-rooted
• 1st premolar may have 2 roots
Accessory digestive organs
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Molars
 They have broad crowns
 Rounded cusps
 6 superiors and 6 inferiors
• 2 first molars
• 2 second molars
• 2 third molars or wisdom teeth
 They have 2 roots
 They grind food into fine pieces
Accessory digestive organs
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Dental formula:
Deciduous
 2,1,0,2
2,1,0,2
Permanent
 2,1,2,3
2,1,2,3
Accessory digestive organs
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Anatomy of the teeth
 Crown
• Clinical
• Anatomical
 Enamel
• It consists mainly of calcium salts
 Gum or gingival
• Gingival sulcus and margin
Accessory digestive organs
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Neck
Root
Cementum
Periodontal ligament
Dentin
Pulp
 Contain blood vessels and nerves
Pulp cavity
Accessory digestive organs
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Odontoblasts
Root canal
Apical foramen
PART C
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Accessory digestive organs
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Salivary glands
 Parotid glands
• Anterior to the ear
• He parotid duct open at the level
of the second superior molar
• Mainly a serous gland
Accessory digestive organs
 Submandibular
gland
• Located on the floor of the mouth
• He submandibular duct opens at
the base of the lingual frenulum
• Serous and mucous gland
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Accessory digestive organs
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Sublingual gland
 Located on the floor of the mouth
 There are many sublingual ducts that
open under the tongue
 Serous and mucous gland
Saliva composition
 Mucin - Forms the bolus
 Serous fluid – contain amylase
Accessory digestive organs
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Histology of the salivary glands
 Mucous cells forming the acini
 Serous cells forming demilunes
around the mucous cells
 Ducts with cuboidal epithelium
Salivary glands
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Accessory digestive organs
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Liver
 Located mainly in the right
hypochondriac region
 4 lobes
• Right, left, caudate, quadrate
 Falciform ligament
• Suspend the liver from the
diaphragm and anterior abdominal
wall
Bile duct system
59
Accessory digestive organs
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Bile
 Produced by the liver
 Responsible for emulsification of the
lipid from the diet
Bile duct system
 Bile canaliculus
• Carries the bile to the duct of the
nearest portal area
Accessory digestive organs
 Bile
ducts carry bile to the:
 Right and left hepatic ducts
 Common hepatic duct
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Accessory digestive organs
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Histology
 Lobules
• Structural and functional units of
the liver
• They have cords of hepatocytes
running away from the central vein
• Hexagonal shape
 Central vein
Histology of the liver
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Accessory digestive organs
 Portal
triad or portal tract
• Located at each of the six corners
of the lobule
• Hepatic artery
• Hepatic portal vein
• Bile duct
 Sinusoids
• Blood-filled
 Kupffer cells
• Macrophage lining the sinusoids
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Accessory digestive organs
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Gallbladder
 Stores the bile not being used
 Concentrates the stored bile
 Cystic duct
Accessory digestive organs
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Pancreas
 It is a retroperitoneal organ
 Endocrine and exocrine organ
 Secretes the pancreatic juice into the
duodenum
 It alkalinizes the chyme coming from
the stomach
 Pancreatic duct or duct of Wirsung
 Accessory pancreatic duct or duct of
Santorini
Accessory digestive organs
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Histology of the pancreas
 Acinar or exocrine pancreas
 Islets or endocrine pancreas
 Septa
• Connective tissue
Microscopic structures to be
identified
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Identify the organ and its layers:
 Mucosa, submucosa, muscularis
externa, adventitia or serosa
Esophagus
 Stratified squamous epithelium
 Gastroesophageal junction
Microscopic structures to be
identified
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Stomach
 Simple columnar epithelium
 Gastric pit
Duodenum
 Villi
• Brush border
• Goblet cells
 Intestinal cripts
 Brunner’s glands
Microscopic structures to be
identified
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Jejunum
 Leafy villi, crypts
 Brush border
 Goblet cells
Ileum
 Villi with goblet cells and brush
border, crypts
 Peyer’s Patch
Microscopic structures to be
identified
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Large intestine
 Cripts, abundant goblet cells
Salivary glands
 Serous acini (demilunes)
 Mucous acini
 Ducts
Pancreas
 Acinar exocrine vs. endocrine
pancreatic islets
Microscopic structures to be
identified
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Liver
 Hexagonal lobules
 Triad
• Hepatic portal vein
• Hepatic artery
• Bile duct
 Central vein
 Sinusoids vs. plates of hepatocytes
Cat structures to be
identified
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Esophagus
Stomach
 Lesser and greater curvatures
 Lesser and greater omentum
Small intestine
 Mesentery proper
 Ileocecal valve
Cat structures to be
identified
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Large intestine
 Mesocolon
 Rectum
 Anus
Liver
Gall bladder
Pancreas