1. Dr. Saima Masood
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2. Digestion
 Processing of food
 Types
 Mechanical (physical)
 Chew
 Tear
 Grind
 Mash
 Mix
 Chemical
Enzymatic hydrolysis
 Carbohydrate
 Protein
 Lipid
2

3. Functions Of Digestive System
 Breakdown of ingested food.
 Morphological adaptations for specialized functions.
 Associated glands discharge their products into the
Lumina of tubular organs.

4. Digestive System Organization
 oral cavity
 esophagus
 stomach
 small and large intestines,
 rectum, and anus—
 Associated glands—salivary glands, liver, and
pancreas.

6. GENERAL STRUCTURE OF
TUBULAR ORGANS
Basic Histological Layers
1.Tunica Mucosa:
 Lines all organs that communicate outside the body
and is protected by a layer of mucous.
 Three Layers
 Epithelium
 Lamina propria
 Lamina Muscularis

7. Tunica Submucosa
 More denser CT than Propria.
 Submucosal Glands.
 Meissner’s Plexus.
 Propria _Submucosa.

8. Tunica Muscularis
 Smooth / Skeletal Muscles
 Moving ingesta in the tract.
 Mixing ingesta with secretions.
 Inner Circular
 Outer longitudinal
 Myenteric ( Auerbach’s Plexus).

9. Tunica Serosa/Adventitia.
 Serosa is a thin layer of loose connective tissue, rich in
blood and lymph vessels and adipose tissue, and a
simple squamous covering epithelium
(mesothelium).
 Adventitia, consisting of connective tissue containing
vessels and nerves, without the mesothelium.

11. THE ORAL CAVITY
 LIPS:
 Junction site of skin and digestive system.
 At Mucocutaneous junction, No hair follicles.
 Mucosa ___ Stratified Squamous Epithelium.
 Propria-Submucosa
 Aggregates of serous or seromucous minor
salivary glands reffered to as labial glands .
 The tunica muscularis consist of skeletal muscle
fibers of the orbicularis oris muscle.

13. Lips

14. Cheeks
 External covering of skin.
 Middle Muscular layer.
 Inner Mucosal layer.
 Ruminants ____ Buccal Papillae.
 Buccal Glands.

15. Cheeks (ruminants)

16. CHEEKS

17. Hard Palate
 Bones covered by a mucosa.
 Rugae.
 Stratified Squamous Keratinized Epithelium.
 Propria _ Submucosa:
 DCT blends with Periosteum.
 Palatine Glands ___ Except pigs.

18. Hard

20. Soft palate
 Mucosal covering
 Skeletal muscles Core.
 Oropharynx:
 St . Sq Epithelium.
 Nasopharynx:
 Caudal side___ St .Sq .Epithelium.
 Cranial side____ Pseudo St . Columnar.

22. Tongue
 Muscular organ covered by mucosa.
 Dorsal surface ___ Keratinized and Thick St. Sq.
 Ventral surface ___ non Keratinized and Thin St. Sq.
 LINGUAL PAPILLAE : Elevations of the oral
epithelium and lamina propria that assume various
forms and functions.
 Filiform ,conical and lenticular ___ Mechanical
 Fungiform ,Vallate and Foliate ___ Gustatory

25. Tongue Contd…..
 Filiform Papillae:
 Most numerous.
 Thread like in shape.
 Thick St Sq .Kert Epi
 Highly vascularized CT
 Does not contain taste buds.

26. Filiform Papillae

29. Conical papillae/
 Larger than filiform.
 Not highly keratinized.
 Occur at root ( Dogs, cats).
Lenticular papillae:
 Flattened ,lens-shaped.
 Mostly present in ruminants.
 Keratinized St. Sq. epithelium.
 DIRCT core.

31. Fungiform papillae
 Scattered among filiform.
 Dome – shaped/dilated upper surface.
 Non kert .St .Sq. epithelium.
 Contain taste buds.
 Circumvallate Papillae
Larger, flattened.
 posterior portion of the tongue
Surrounded by sulcus/furrows.
Gustatory glands

32. Fungiform Papillae

34. Vallate papilla

36. Foliate Papillae
 Parallel folds of Mucosa.
 Contain many taste buds.
 poorly developed
in humans.
 Absent in Ruminants.
 Rudimentary in cats.

38. Taste Buds
 Barrel-shaped structures of specialized epithelial cells .
 Soft palate ,epiglottis , Pharynx.
 Taste Pore.
 Types of cells

40. Taste Buds

42. Esophagus
 Muscular tube that
transports foodstuffs
from the mouth to the
stomach.
 Tunica Mucosa
 Submucosa
 Tunica Muscularis
 Adventitia/Serosa

45. 45
Esophagus histology

46. Esophagus-Stomach Junction
 Carnivores: Esophagus with stratified squamous ep.
Changes abruptly into simple columnar glandular
epithelium of stomach.
 Horse and pig: Stratified squamous epithelium
extends throughout the nonglandular portion of the
mucosa of the stomach.
 Ruminants: Stratified squamous epithelium lines the
entire forestomach.

47. CARDIO-OESOPHAGEAL JUNCTION

48. Stomach (contd.)
 The stomach is a sack-like organ lined with a
glandular, absorptive mucosa.
 The digestive enzymes in the acidic environment of
the lumen, in concert with contractions of the
muscular wall of the organ initiate the breakdown of
the ingesta.

49. Nonglandular Region of the
Gastric Mucosa In some animals, in addition to the glandular portion,
there exist a nonglandular region of the mucosa lined
with stratified squamous epithelium with varying
degrees of keratinization.
 Horse: The nonglandular portion extends quite a
distance from the esophagus and ends at the margo
plicatus.
 Ruminants: The nonglandular portion is extensive
and lines the entire forestomach
 (rumen, reticulum, and omasum).
 Carnivores and pigs do not have this nonglandular
portion. The entire stomach is glandular.

50. Glandular Region(STOMACH)
 Three regions
 cardia
 fundus
 pylorus
 Gastric folds . The mucosa and submucosa of the
undistended stomach lie in longitudinally directed folds
known as rugae
 Gastric pits.
 Gastric glands.

51. Glandular mucosa (stomach)
 Epithelium
 The surface epithelium of the stomach is made up of
surface mucous cells. The continuous secretion of this
material (mucous blanket) protects the lining of the
stomach from the acid produced by the gastric glands.
 Lamina propria This contains loose connective
tissue, lymphoid cells and occasional lymphoid
nodules.
 The gastric glands are also located in thislayer
 Muscularis mucosae.---- three layers usually.

52. 1.Cardiac Gland region:
 These are branched tubular mucous glands. The
mucous secreted, along with that of the
 surface epithelium, protect the lining of the stomach.
 Cuboidal cells--- mucus and lysozyme.
Shallow gastric pits.

53. Esophagus-Stomach

54. Fundus (stomach)
 Well developed in all animals.
 Proper gastric glands.
 Three portions
1.Short Neck
2.Long Body
3.Dilated Fundus
Four Types of Cells in gastric
glands.

55. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig 25.13a, c, d

56. Mucous Neck Cells
 Present in clusters or as single cells.
 At Neck region of glands.
 Irregular in shape.
 Basal Nucleus.
Secretory granules.
- Contain mucinogen granules in apical cytoplasm, while
nuclei are basally situated basally.
- Produces soluble mucus

57. Oxyntic (Parietal) Cells
 Rounded or pyramidal cells.
 Eosinophilic cytoplasm
They are large, ovoid or polyhedral cells with a large central nucleus.
 - More numerous in the upper half of the gland than in the lower half
 - Secretes HCL and intrinsic factor.
 Intrinsic factor combines with vitamin B12 to form a complex
necessary for erythrocytes formation.


58. Chief (Zymogenic) Cells
 Lower region of the tubular glands.
 Pyramidal/Cuboidal.
 Rounded nucleus.
 Highly Basophilic.
 pepsinogen
active proteolytic enzyme pepsin

59. Proper Gastric region

62. Fundic Glands

63.  GIT Hormones release.
 Gastrin
 Secretin
 Cholecystokinin
 GIP
 Appear clear.

64. Pyloric Gland region.
 Simple branched ,coiled tubular.
 Mucous secretory cells
 Deeper pits
 Pyloric sphincter.

65. Stomach (Layers)
 Stratum compactum is a layer of collagen and
elastic fibers between the glands and the
 muscularis mucosae. It is often encountered in the
carnivores.
 Muscularis mucosae are usually made up of two
layers of smooth muscles. Strands of
 smooth muscle cells can be seen extending upward in
between the gastric glands.
 Contraction of these strands helps to empty the gastric
glands.

66. Stomach (layers)
 Submucosa
 In the connective tissue of the submucosa are lymphoid
cells, blood vessels and
 lymphatics. Parasympathetic ganglia, known as
submucosal / Meissner’s plexus, are
 found here. They, along with sympathetic fibers, are
involved in the contraction of the
 smooth muscle cells.
 Muscularis externa
 The outer wall of the stomach contains layers of smooth
muscles. In addition

67. The Small Intestine
 Primary role in the digestion and absorption of nutrients –
About 90%
- Averages 6 m in length
_ Diameter ranging from 4 cm to 2.5 cm.
- The Mucosa:
1- plicae circulares
- transverse folds in the intestinal lining .
- permanent and do not disappear.
2. villi
project microscopic finger-like pieces of tissue.
3.microvilli
The crypts of Lieberkühn

68. Small intestine
 3 subdivisions –
 duodenum
 jejunum
 ileum

69. Cells of Small Intestine
 Absorptive cells
 Goblet cells
 Enteroendocrine cells
 Paneth cells
 Stem cells

70. Columnar absorptive cells
 Responsible for absorbing nutrients.
 The brush border.
 . Goblet cells
secrete mucus to promote movement .
Enteroendocrine cells
secrete hormones to regulate secretion into the GI tract
Paneth cells
At the bottoms of the crypts
secrete lysosomal enzymes

71. Layer Duodenum Jejunum Ileum
serosa normal normal normal
muscularis externa
longitudinal and
circular layers, with
Auerbach's (myenteric)
plexus in between
same as duodenum same as duodenum
submucosa
Brunner's glands and
Meissner's
(submucosal) plexus
no BG no BG
mucosa: muscularis
mucosae
normal normal normal
mucosa: lamina propria no PP no PP Peyer's patches
mucosa: intestinal
epithelium
simple columnar.
Contains goblet cells,
Paneth cells
Similar to duodenum.
Villi very long.
Similar to duodenum.
Villi very short.

72.  Lamina propria of each villus contains an
extensive network of capillaries - absorb and
carry nutrients to the hepatic portal
circulation
 Also contain a terminal lymphatic called a
lacteal – transports materials that cannot
enter the capillaries such as large lipid-
protein complexes
Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig 25.15

73. Histology of the Intestinal Wall
Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig 25.15d,e

74. High power view of
the duodenal Mucosa

75. Gross view and low-power view
of the ileum

76. High-power view of the Ileum
demonstrating Peyer’s patches

77. Large Intestine
 The terminal part of the digestive system.
 Absorbs water and minerals
Three subdivisions:
CECUM
COLON
 Ascending
 Transverse
 Descending
RECTUM
MUCOSA

78. Large Intestine

79. High power view of the colon
demonstrating intestinal glands

80. Histology of the Large Intestine
 Characteristics that distinguish the large
intestine from the small intestine:
1- wall is relatively thin.
2- lacks villi
3- goblet cells are much more abundant.
4- distinctive intestinal crypts with deeper glands dominated
by goblet cells.
5- large lymphoid nodules are scattered throughout the
lamina propria and extend into the submucosa.
6- longitudinal layer of the muscularis externa reduced to the
muscular bands of the taeniae coli.

81. Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Figure 25.19

83. RUMINANT STOMACH
 The ruminant stomach has four parts: 1. Rumen
(“paunch”). 2. Reticulum (“honeycomb tripe”). 3. Omasum
(“book”). and 4. Abomasum.
 The first three parts form the forestomach and are
histologically quite different from the abomasum that is
similar to the glandular stomach discussed in the previous
section.
 At birth, the forestomach is underdeveloped and, not until
the ingestion of solid food .
 Stratified squamous epithelium lines the forestomach. This
epithelium has absorptive capabilities and is structurally
different from the stratified squamous epithelium in other
 organs.

84. Forestomach (contd.)
 The cells have abundant mitochondria, especially in
the spinosum layer, which allows active transport of
nutrients.
 Beneath the epithelium is an elaborate network of
 capillaries.
 Digestive glands are not present in the forestomach.

85. Rumen
 The mucosa forms finger-like papillae containing
highly vascularized connective tissue core and covered
by stratified squamous epithelium.
 The epithelium is involved in the absorption of short-
chain fatty acids (i.e. sodium salts, the microbial
breakdown products of cellulose).
 Muscularis mucosae are absent in this part of the
forestomach.
 The muscularis externa contains two layers of smooth
muscle fibers. Myenteric plexus can be found between
these layers

86. Ruminant Stomach (Rumen)

87. Ruminant Stomach (Rumen)

88. Reticulum
 The mucosa contains rows of folds (laminae) that form
square honeycomb-like compartments called cells.
 On the surface of the laminae are short, conical
projections
 called papillae.
 The stratified squamous epithelium also absorbs short-
chain fatty acids.
 Near the margins of the folds are strands of smooth muscle
fibers forming the muscularis mucosae.
 This is the most cranial part of the forestomach. Food and
sometimes non-food “objects”drop in here first .

89. Ruminant Stomach (Reticulum)

90. Ruminant Stomach (Reticulum)

91. Omasum
 The mucosa and portions of muscularis mucosae form
parallel folds that resemble pages of an open book.
 The folds are called laminae and they have little
projections (papillae)on their surfaces.
 The mucosal surface is covered by stratified squamous
epithelium. This absorbs water and other nutrients.

92. Omasum (contd.)
 The core of the laminae are quite characteristic with
three layers of smooth muscle.
 Extending upward from the muscularis mucosae are
fibers that form the two outer layers.
 Sandwiched between these two layers is a single inner
layer of smooth muscle.
 This is derived from the muscularis externa and the
fibers are perpendicular to those of the outer layers.

93. Ruminant Stomach (Omasum)

94. Ruminant Stomach (Omasum)

95. Accessory Glandular Digestive Organs
 the salivary glands
 the liver
 the gallbladder
 the pancreas
- salivary glands, liver, and pancreas have
exocrine functions

96. There are Major and Minor
groups of Salivary Glands:
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97.  consists three
pairs of major
glands,
parotid,
submandular
sublingual
glands.
a) Major groups
of salivary
glands
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98.  may be found in the :
Mucosa of the lips(labial glands),
Mucosa of the palate(palatal
glands)
Tongue ( lingual glands)
Pharyngeal mucosa(pharyngeal
glands)
cheeks,
larynx, trachea
b) Minor groups of salivary
glands
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99. Salivary glands
(tuboalveolar glands)
 Intrinsic salivary glands –
within mucosa
 Secrete saliva all the time to
keep mouth moist
 Extrinsic salivary glands
 Paired (2 each)
 Parotid
 Submandibular
 Sublingual
 External to mouth
 Ducts to mouth
 Secrete saliva only right
before or during eating
99
Saliva: mixture of water, ions,
mucus, enzymes
keep mouth moist
dissolves food so can be
tasted
moistens food
starts enzymatic
digestion
buffers acid
antibacterial and
antiviral

100. Structure of salivary glands
 Compound Glands.
 Several lobes.
 Lobules.

101. Shapes of secretory Units

102.  Salivary gland tissue consists of
parenchymatous secretory cells and
stromal connective tissue which
consists of
blood vessels
nerves
 excretory ducts
fibroblasts
lymphocytes and fat cells.
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103. Myoepithelial cells
These cells are closely
related to the secretory and
the intercalated duct system.
The body of the cell is small
filled with a flattened nucleus
These cells are considered to
have a contractile function
helping to expel secretions
from the lumina of the
secretory units and the ducts.
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104. SALIVARY GLAND SECRETORY UNIT
 Composed of;
 terminal glndular acini
 Salivary Gland Tissue -ducts
Myoepithelial cells
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105. Glandular acini of Salivary Glands
Classified as either:
Serous cells: produce a thin watery secretion
Mucous cells: produce a more viscous secretion or
 mixed
The parotid gland acini
contain predominately serous
cells,
 submandibular gland acini
are mixed.
 sublingual and minor
salivary glands have
predominately mucous acini.
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106. Salivary Gland Tissue -ducts
Intercalated
Secrete mucins and
regulate electrolyte
concentration of the saliva
striated ducts
Next to intercalated ducts
 Actively secrete fluids
Excretory ducts
Transports saliva
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107. The Parotid Salivary Gland
 Predominantly Serous.
 Few Mucous S.units ___ Dogs & cats.
 Compound Acinar Gland.
 Numerous lobules with CT septa.
 Pyramidal-shaped cells.
 Apical part---Zymogen granules.
 Basal nuclei.
 Myoepithelial cells.

108. PAROTID GLANDS

109. Sublingual Salivary Glands
 Seromucous glands.
 Compound Tubuloacinar .
 No. Of Mucus and Serous acini diff in species.
 Cattle, Sheep & pig --- Mucus acini more.
 Intercalated & Striated ducts---less prominent
 More developed in Horses and Ruminants.
 Main duct---St. cuboidal epithelium.

110. SUBLINGUAL GLANDS

111.  second largest salivary
glands in the body.
 Each submandibular
gland is divided into
superficial and deep lobes
by the posterior edge of
the mylohyoid muscle
It produces mucoserous
secretions
Submandibular Gland
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113. Pancreas
- The pancreas contains multiple ducts.
- the main pancreatic duct runs from the tail to the
head of the pancreas.
- a smaller accessory pancreatic duct. They join the
common bile duct to empty into the duodenum.

114. Histological Organization
- the pancreas has both exocrine and endocrine function
- the septa between pancreatic lobules with interlobular
ducts .
- Secretory portions are called acini.
- The scattered endocrine islets of Langerhans
- are paler staining.
- It is a compact mass of epithelial cells that receive rich
vascular supply
- the alpha cells secrete glucagon,
- the beta cells secrete insulin, and the delta cells secrete
somatostatin

115. THE EXOCRINE PANCREAS
 Most of the pancreas contains exocrine acini.
Pancreatic enzymes are
 Proteases
 lipases
 amylases.
 pancreatic acinar / secretory cells

116. PANCREAS HISTOLOGY

117. PANCREATIC ISLETS