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
small and large intestines,
rectum, and anus—
Associated glands—salivary glands, liver, and
6. GENERAL STRUCTURE OF
Basic Histological Layers
Lines all organs that communicate outside the body
and is protected by a layer of mucous.
8. Tunica Muscularis
Smooth / Skeletal Muscles
Moving ingesta in the tract.
Mixing ingesta with secretions.
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
Adventitia, consisting of connective tissue containing
vessels and nerves, without the mesothelium.
11. THE ORAL CAVITY
Junction site of skin and digestive system.
At Mucocutaneous junction, No hair follicles.
Mucosa ___ Stratified Squamous Epithelium.
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.
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…..
Thread like in shape.
Thick St Sq .Kert Epi
Highly vascularized CT
Does not contain taste buds.
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
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
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
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)
Gastric folds . The mucosa and submucosa of the
undistended stomach lie in longitudinally directed folds
known as rugae
51. Glandular mucosa (stomach)
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
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.
56. Mucous Neck Cells
Present in clusters or as single cells.
At Neck region of glands.
Irregular in shape.
- Contain mucinogen granules in apical cytoplasm, while
nuclei are basally situated basally.
- Produces soluble mucus
57. Oxyntic (Parietal) Cells
Rounded or pyramidal cells.
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.
active proteolytic enzyme pepsin
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
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
66. Stomach (layers)
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.
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 –
- 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.
project microscopic finger-like pieces of tissue.
The crypts of Lieberkühn
69. Cells of Small Intestine
70. Columnar absorptive cells
Responsible for absorbing nutrients.
The brush border.
. Goblet cells
secrete mucus to promote movement .
secrete hormones to regulate secretion into the GI tract
At the bottoms of the crypts
secrete lysosomal enzymes
71. Layer Duodenum Jejunum Ileum
serosa normal normal normal
circular layers, with
plexus in between
same as duodenum same as duodenum
Brunner's glands and
no BG no BG
normal normal normal
mucosa: lamina propria no PP no PP Peyer's patches
Contains goblet cells,
Similar to duodenum.
Villi very long.
Similar to duodenum.
Villi very short.
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.
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
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
84. Forestomach (contd.)
The cells have abundant mitochondria, especially in
the spinosum layer, which allows active transport of
Beneath the epithelium is an elaborate network of
Digestive glands are not present in the forestomach.
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
The muscularis externa contains two layers of smooth
muscle fibers. Myenteric plexus can be found between
The mucosa contains rows of folds (laminae) that form
square honeycomb-like compartments called cells.
On the surface of the laminae are short, conical
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 .
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.
97. consists three
pairs of major
a) Major groups
98. may be found in the :
Mucosa of the lips(labial glands),
Mucosa of the palate(palatal
Tongue ( lingual glands)
b) Minor groups of salivary
99. Salivary glands
Intrinsic salivary glands –
Secrete saliva all the time to
keep mouth moist
Extrinsic salivary glands
Paired (2 each)
External to mouth
Ducts to mouth
Secrete saliva only right
before or during eating
Saliva: mixture of water, ions,
keep mouth moist
dissolves food so can be
102. Salivary gland tissue consists of
parenchymatous secretory cells and
stromal connective tissue which
lymphocytes and fat cells.
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.
105. Glandular acini of Salivary Glands
Classified as either:
Serous cells: produce a thin watery secretion
Mucous cells: produce a more viscous secretion or
The parotid gland acini
contain predominately serous
submandibular gland acini
sublingual and minor
salivary glands have
predominately mucous acini.
106. Salivary Gland Tissue -ducts
Secrete mucins and
concentration of the saliva
Next to intercalated ducts
Actively secrete fluids
111. second largest salivary
glands in the body.
gland is divided into
superficial and deep lobes
by the posterior edge of
the mylohyoid muscle
It produces mucoserous
- 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
- 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
- the alpha cells secrete glucagon,
- the beta cells secrete insulin, and the delta cells secrete
115. THE EXOCRINE PANCREAS
Most of the pancreas contains exocrine acini.
Pancreatic enzymes are
pancreatic acinar / secretory cells