GI System Histo

1
GI System Histo
2
Lip
Lip. This is a section from the inner portion of
a lip. Notice that it is lined by a
non-keratinized stratified squamous epithelium.
Deep to the epithelium is a fibroelastic
connective tissue containing mucous-secreting
labial glands (red arrows). The core of the lip
contains skeletal muscle (oris orbicularis not
shown). LLumen.
3
Filiform Papillae
Filiform Papillae. The tongue consists of a mass
of skeletal muscle covered by a mucous membrane.
The mucous membrane is smooth on the ventral
surface, but irregular on the dorsum due to the
presence of numerous papillae. Several filiform
papillae (red arrows) are illustrated in this
micrograph. These papillae are partially
keratinized and serve to roughen the surface of
the tongue to aid in licking. In some species
such as cats, the filiformes have a higher degree
of keratinization which yields a very raspy
surface. Skeletal muscle is located in the area
below the red line.

4
Circumvallate Papilla
Circumvallate Papilla. The tongue contains 7-12
circumvallate papillae in the area of the sulcus
terminalis. This is a low magnification section
of tongue illustrating one of these papillae (red
arrow). Taste buds are present on the lateral
surfaces of the papilla (area encircled in
green). A trough surrounds each of these
papillae. Emptying into these troughs are the
serous secretions of the glands of Von Ebner
(yellow arrows).
5
Circumvallate Papilla
Circumvallate Papilla. This is a higher
magnification of the previous image illustrating
the serous units of Von Ebners glands (yellow
arrow) and its duct (red arrow) emptying into the
trough surrounding a circumvallate papilla of the
tongue. Note the lighter staining structures
(taste buds) on the sides of the papilla
(encircled in green).
6
Taste Buds
Taste Buds. This is a high magnification of the
side of a circumvallate papilla illustrating
several taste buds (yellow arrows). The three
cells types associated with this structure
include sensory cells, supporting or
sustentacular cells, and basal cells. The
darker-staining sensory cells (white arrows) can
be easily distinguished from the sustentacular.
7
Parotid Gland
Parotid Gland. The major salivary glands include
parotid, submandibular, and sublingual. The is a
low magnification image of a section of parotid
gland. The secretory units of this gland are
entirely serous (yellow arrows). Numerous
intralobular (striated) ducts are present (orange
arrows). Duct cells tend to stain a light pink.
Several fat cells are scattered throughout the
gland (red arrows).
8
Parotid Gland
Parotid Gland. This is a thin section (1.5µm)
of a parotid gland illustrating two intercalated
ducts (red arrows). These are the first ducts off
of the secretory units and generally have a
smaller cross-sectional diameter than the
secretory units.
9
Submandibular Gland
Submandibular Gland. The submandibular gland
contains about 80 serous cells and 5 mucous
cells. In this image, examples of serous cells
are indicated by yellow arrows. Mucous cells
(black arrows) exhibit very little staining.
Intralobular ducts are indicated by he orange
arrows and stain light pink.
10
Sublingual Gland
Sublingual Gland. The sublingual gland is
primarily mucous-secreting contains about 30
serous cells and 60 mucous cells. In this image,
examples of mucous cells are indicated by black
arrows. Numerous serous demilunes (green arrows)
capping the mucous units are present. The tip of
the orange arrow is in the lumen of an
interlobular duct.
11
Sublingual Gland
Sublingual Gland. The sublingual gland is
primarily mucous-secreting contains about 30
serous cells and 60 mucous cells. In this image,
examples of mucous cells are indicated by black
arrows. The serous cells are indicated by the red
arrows. Numerous intralobular ducts are present
(green arrows). The blue arrow is pointing to an
interlobular duct. Note that this type of duct
has a noticeable amount of connective tissue
associated in contrast to the intralobular ducts.
12
Sublingual Gland
Sublingual Gland. This is a high magnification of
a sublingual gland illustrating the associated
cell types. Examples of mucous cells are
indicated by black arrows. Numerous serous
demilunes (yellow arrows) capping the mucous
units are present.
13
Dental Lamina
Dental Lamina. The first sign of tooth
development is the formation of a dental lamina
along the position of the future dental arch.
Following the initiation process, there is
increased mitotic activity of the epithelial
cells in this area and then a downward growth of
these cells as the mitotic activity continues
(black arrow). This forms a continuous ridge,
called the dental lamina, along the future dental
arch. Associated with the dental lamina formation
is an increase in the density of mesenchymal
cells in this area (red arrow).
14
Bud Stage
Bud Stage. Along the dental lamina at 10 sites
each in the upper jaw and the lower jaw, there is
increased mitotic activity leading to the
formation of the enamel organ. As the name
implies these cells will be involved in the
formation of enamel. The enamel organ undergoes
several conformational changes due to
histodifferentiation. The dental lamina narrows
and the enamel organ is somewhat rounded. This is
referred to as the Bud Stage (black arrow). Note
the increased density of mesenchymal cells (red
arrow). These cells will eventually develop into
structures associated with the tooth.
15
Cap Stage
Cap Stage. The enamel organ continues to
proliferate and increase in size. An increased
density of mesenchymal cells occurs on the deep
surface of the enamel organ. These mesenchymal
cells are in the process of forming the dental
papilla, which will develop into the connective
tissue of the dental cavity. Some of these cells
will develop into odontoblasts responsible for
the formation of dentin. There is unequal growth
of the enamel organ (black arrows) leading to the
formation of a shallow invagination on the deep
surface. This is recognized as the Cap Stage. The
blue arrow indicates the dental lamina.
16
Bell Stage
Bell Stage. With continued growth and
histodifferentiation, the enamel organ assumes a
bell shape. The mesenchymal cells on the deep
surface of the enamel organ have developed into
the Dental Papilla (DP), which now fills the
concavity of the bell. Cells on the outer portion
or periphery of the dental papilla will develop
into odontoblasts responsible for the formation
of dentin. The cells in the center of the enamel
organ differentiate into the Stellate Reticulum
(black arrow). These cells have a stellate
appearance due to numerous cytoplasmic processes.
The spaces between the cells come to contain
fluid, which will help to cushion and protect the
forming surface of the tooth. The outer cells
differentiate into the Outer Enamel Epithelium
(red arrow). The inner cells of the enamel organ
(immediately surrounding the dental papilla)
differentiate into the Inner Enamel Epithelium
(green arrow). The cells of the inner enamel
epithelium will develop into ameloblasts
responsible for the formation of enamel. The thin
pink line between the inner enamel epithelium and
the dental papilla (orange arrow) is the basal
lamina of the enamel organ. The mesenchymal cells
surrounding the bell (dashed black arrow) form
the Dental Sac, which will go on to form
Cementum, Periodontal Ligament, and Alveolar
Bone. The blue arrow indicates the dental lamina.
17
Bell Stage
Bell Stage. With further development of the bell
stage, a secondary dental lamina (red arrow)
forms off of the primary dental lamina (green
arrow), projecting toward the lingual side of the
forming tooth. The permanent teeth develop from
the tip of the secondary laminae. A very early
permanent tooth in the bud stage appears to be
present in this image. DPDental papilla.
18
Developing Tooth (Upper).
          
Developing Tooth (Upper). This is a section of
the upper portion of a tooth well along in its
development. Odontoblasts (blue arrow) on outer
rim of the dental pulp (former dental papilla)
are in the process of depositing dentin (green
arrow). During this process, they move in a
direction toward the dental pulp. The ameloblasts
(red arrow) are in the process of depositing
enamel (black arrow). During this process, they
move in a direction away from the dentin.
19
Developing Tooth (Lower).
Developing Tooth (Lower). This is a section of
the lower portion of the developing tooth
illustrated on the previous page. The future root
will develop in the area of the yellow arrow.
20
Periodontal Ligament (PDL)
PDL. This is an image of an edge of a tooth on
the left and a portion of the alveolar bone on
the right (black arrows). The cementum (C) is
located on the outer edge of the dentin (D). The
green arrow points to the junction between the
dentin and the cementum. The Periodontal Ligament
(PDL) inserts into the cementum and the alveolar
bone via Sharpeys fibers (red arrows). The PDL
serves to anchor the tooth in the alveolar
socket.
21
Esophagus
Esophagus. This is a low magnification of the
esophagus. It is lined by a non-keratinized
stratified squamous epithelium (orange arrow).
Deep to the epithelium is a thin lamina propria
(blue arrow). Deep to the lamina propria is the
muscularis mucosae (red arrow) consisting of
smooth muscle. These three layers constitute the
mucosa. The submucosa (purple arrow), located
deep to the mucosa, is a band of relatively dense
connective tissue. The next layer, the muscularis
externa, consists of muscle. The muscle is
skeletal in the upper third of the esophagus (a
continuation of the skeletal muscle of the
oropharynx), smooth muscle in the lower third,
and mixed in between. This image is from the
lower third of the esophagus illustrating an
inner band of circularly arranged muscle (green
arrow) and an outer band of longitudinally
arranged muscle (black arrow). A small lymphatic
nodule is present (yellow arrow). Esophageal
glands normally scattered throughout the
esophagus are not present in this section.
22
Esophagus
Esophagus. This is a low magnification of the
esophagus (from the upper third). In this image,
a submucosal esophageal gland is illustrated
(black arrow). These glands are primarily
mucous-secreting. Some serous-secreting cells are
scattered within the gland. Can you identify the
muscularis mucosae??
23
Stomach
Stomach. This is a low magnification image of a
section through the stomach illustrating its
overall general structure. Some variation occurs
in the cardia, fundus/body, and the pyloris. The
fundus and the body are histologically identical.
As can be noted in this image, the epithelial
lining invaginates into the mucosa forming
gastric pits or foveolae (red arrows). The pits
are shallowest in the cardia and deepest in the
pylorus. Several gastric glands open into the
bottom of each pit. Mucous-secreting cells line
the surface and the opening of the pit (yellow
line to the surface). The thick mucous secreted
by these cells protects the surface of stomach.
The neck of the gastric gland (yellow line to red
line) is lined by mucous neck cells and parietal
(oxyntic) cells. A few regenerative cells are
located in this region. The base of the glands
contains chief (zymogenic) cells, parietal cells,
and a few enteroendocrine cells. The submucosa is
indicated by the black arrow the muscularis
externa is encircled in blue.
24
Stomach
Stomach. This is a higher magnification of the
previous image illustrating a somewhat better
view of the gastric mucosa. The pits lie in the
approximate area between the yellow line and the
lumen (L). The red arrows point to two of the pit
openings. The necks of the glands are located in
the area between the yellow line and the red
line the base of the glands lie between the red
and black lines. The muscularis mucosa is
indicated by the blue arrow.
25
Stomach
Stomach. This image is a high magnification of
the base of fundic glands. The chief (zymogenic)
cells (black arrows) make up the larger
population of the secretory cells. Parietal cells
(red arrows) are scattered among the chief cells.
These latter cells are responsible for the
production of hydrochloric acid and gastric
intrinsic factor.
26
Duodenum
Duodenum. This is a section from the duodenum,
the first section of the small intestine. The
mucosa with its broad villi is encircled in
black. Deep to the mucosa is the submucosa (blue
arrow) containing Brunners glands (red arrow), a
distinctive feature of the duodenum. Surrounding
the submucosa is the muscularis externa (green
arrow) consisting of inner circular and outer
longitudinal layers of smooth muscle. The outer
layer is the serosa consisting of the adventitia
covered by mesothelium.
27
Jejunum
Jejunum. This is a section through the jejunum
illustrating numerous villi projecting into the
lumen (L). The villi consist of a core of lamina
propria (blue arrow). This layer is comprised of
loose connective tissue containing lots of
lymphocytes and plasma cells. The orange arrow
points to the lumen of a lacteal. The villi are
lined by a simple columnar epithelium containing
microvilli. Goblet cells are also present in the
lining epithelium, but not evident at this
magnification. Between the bases of the villi,
the surface invaginates to form the crypts of
Lieberkühn. The submucosa is indicated by the red
arrow the muscularis with its inner circular and
outer longitudinal smooth muscle layers by the
green arrow. The adventitia is not present on
this section. The image on the right is a higher
magnification of the area encircled in black. The
black arrow indicates a goblet cell. Microvilli
are indicated by the red arrow.
28
Jejunum
Jejunum. This is a section through the jejunum
illustrating numerous villi projecting into the
lumen (L). The villi consist of a core of lamina
propria (blue arrow). This layer is comprised of
loose connective tissue containing lots of
lymphocytes and plasma cells. The orange arrow
points to the lumen of a lacteal. The villi are
lined by a simple columnar epithelium containing
microvilli. Goblet cells are also present in the
lining epithelium, but not evident at this
magnification. Between the bases of the villi,
the surface invaginates to form the crypts of
Lieberkühn. The submucosa is indicated by the red
arrow the muscularis with its inner circular and
outer longitudinal smooth muscle layers by the
green arrow. The adventitia is not present on
this section. The image on the right is a higher
magnification of the area encircled in black. The
black arrow indicates a goblet cell. Microvilli
are indicated by the red arrow.
29
Lacteal
Lacteal. This is a high magnification of a villus
of the jejunum illustrating a lacteal (yellow
arrow), which is an example of lymphatic
capillaries typically found in villi. Lacteals
are lined by endothelium.
30
Myenteric Plexus
Myenteric Plexus. This is a high magnification of
the muscularis externa of the small intestine.
The inner circular layer of smooth muscle is
indicated by the yellow line and the outer layer
by the red line. Located between the two layers
is the myenteric (Auerbachs) plexus,
parasympathetic ganglion (black arrows). Numerous
such ganglia are present in the wall of the small
intestine. The myenteric plexus control the
motility of the muscularis externa and therefore
peristalsis. Similar ganglia are located in the
submucosa and are known as submucosal
(Meissners) plexuses. The parasympathetic fibers
of the submucosal plexus control the secretory
activity of the epithelial lining cells and of
the glands in the lamina propria. They also
control the movement of the muscularis
mucosae.The image on the right is a higher
magnification of a myenteric plexus. The black
arrows in the image on the right point to three
perikarya, which are the cell bodies of
post-ganglionic neurons.
31
Colon
Colon. This is a low magnification of a section
through the colon. This organ has no villi but
does contain lots of crypts of Lieberkühn. The
cells of the crypts are similar to those of the
small intestine except for the absence of Paneth
cells. The density of goblet cells increases
along the length of the colon while the
absorptive cells decrease in number. The mucosa
occupies the area between the black line and the
lumen (top of image). The submucosa is located
between the black and red lines. One of three
taenia coli that are located around the colon is
illustrated at the bottom of the image (TC). The
image on the right is a higher magnification of
the colon illustrating the numerous the crypts of
Lieberkühn (black arrows). The lining cells
include absorptive cells, goblet cells, some
regenerative cells and enteroendocrine cells. The
latter two groups of cells are found near the
base of the crypts.
32
Colon
Colon. The image on the left is a low
magnification image of the colon. The mucosa
contains lots of crypts of Lieberkuehn (red
arrow). Just deep to the mucosa is the submucosa
(black arrow). The muscularis mucosa ( green
arrows) contains an inner circular and outer
longitudinal layer of smooth muscle. An
adventitia is indicated by the blue arrow. The
image on the right is an enlarged magnification
of the mucosa illustrating the crypts of
Lieberkuehn (black arrows). The crypts are lined
by goblet and absorptive cells.
33
Liver
Liver. This is a low magnification image of a
section through the liver. Several lobules (L)
are outlined by their surrounding interlobular
connective tissue (black arrows). The lobules are
roughly hexagonal in shape. Portal triads
(portal systems) are located at the corners of
the lobules (black rings). Blood from branches of
portal veins and hepatic artery located in the
triads enters sinusoids and passes to the central
veins located at the center of the lobules (red
arrows).
34
Liver
Liver. This is a high magnification image of a
section through a portal triad (portal system)
which is outlined in yellow. The triads contain a
hepatic portal vein (black arrow), hepatic
arteriole (red arrow), bile duct (green arrow),
and lymphatic vessels (blue arrow).
35
Liver
Liver. In this image, a branch (yellow arrow) of
a very large portal vein (PV) is shown to be
emptying into sinusoids (black arrows). Also
illustrated are two bile ducts (green arrows) and
an arteriole (branch of hepatic artery red
arrow).
36
Liver
Liver. In this image, several sinusoids (blue
arrows) are illustrated to be emptying into a
central vein located in the center of a lobule.
All the white spaces present in this image are of
sinusoids.
37
Liver
Liver. In this image, several sinusoids (white
spaces) are illustrated. One such sinusoid (blue
arrow) is seen emptying into a central vein (red
arrow).
38
Liver
Liver. This is a high magnification image of
several hepatocytes. When bile is secreted by the
hepatocytes, it first enters the bile canaliculi
(red arrows). The bile then empties into the
canals of Herring and then the bile ducts of the
portal triads.
39
Gall Bladder
Gall Bladder. The functions of the gall bladder
include the storage and concentration of bile.
This image is of a section through the gall
bladder showing the highly folded and complex
mucosa (red arrows). The mucosa is lined by a
simple columnar epithelium containing lots of
microvilli. Bands of smooth muscle (Blue arrows)
found in the wall. When the muscle contracts the
contents of the bladder are expressed into the
cystic duct. What is the stimulus for the smooth
muscle contraction?? The outer part of the wall
is covered with serosa (adventitia plus
mesothelium).
ParasympatheticNS via the NT ACH stimulates the
smooth muscle of the gallbladder to secrete bile,
sympathetic inhibits it.
40
Gall Bladder
Gall Bladder. These images are higher
magnifications of the gall bladder illustrating
the lamina propria of the mucosa (red arrows) and
the lining of simple columnar epithelium (green
arrows). The blue arrows are pointing to the
smooth muscle.
41
Pancreas
Pancreas. The pancreas is a mixed gland in that
it has both endocrine and exocrine components.
The endocrine portion consists of small clusters
of cells that form what is referred to as Islets
of Langerhans. These cells synthesize various
hormones as insulin, glucagons, somatostatin,
etc. The rest of the pancreas synthesize and
secrete a variety of digestive enzymes. Some
cells, the centroacinar cells, secrete
bicarbonates. In this image, the islets of
Langerhans is indicated by the green arrows. Most
of the cells (eliminating the islet cells) are
serous-secreting cells of the exocrine part of
the pancreas (red arrows). Several intralobular
ducts are present (blue arrows).
42
Pancreas
Pancreas. This section of pancreas is a thin
section (1.5µm). Two islets are illustrated
(green arrows). Serous-secreting cells are
indicated by the red arrows. It is difficult to
visualize the centroacinar cells at this
magnification.
43
Pancreas
Pancreas. This is a higher magnification of the
pancreas with a lone islet in the center of the
image. The black arrows are pointing to
centroacinar cells, which are responsible for the
secretion of bicarbonates. What is the
stimulation for their secretion of the
bicarbonates??
Secretin This hormone is also a product of
endocrinocytes located in the epithelium of the
proximal small intestine. Secretin is secreted in
response to acid in the duodenum, which of course
occurs when acid-laden chyme from the stomach
flows through the pylorus. The predominant effect
of secretin on the pancreas is to stimulate duct
cells to secrete water and bicarbonate. As soon
as this occurs, the enyzmes secreted by the
acinar cells are flushed out of the pancreas,
through the pancreatic duct into the duodenum