Reading Material-Digestive Tract
LM SECTIONS:
1.
The body of the tongue
1)
Material: Vertical section of the body of tongue
2)
Stain: H.E.
3) Requirement: Observe the filiform papillae and fungiform
papillae.
4)
Observation:
Naked eye: The mucosa is purple-red stained and covers the surface
of tongue. In the center is the thick deep rod-stained muscle.
Low power: At first, distinguish the dorsal and ventral surface of
tongue. The mucosa of the dorsal surface is irregular and projects
outwar to form a number of papillae consisting of stratified squamous
epithelium and lamina propria. According to the morphology, the
papillae can be classified into filiform papillae and fungiform
papillae. Filiform papillae are quite numerous and are elongated
conical in shape. The cornified tips usually appear as candle towards
one side. The layers of epithelium are more, and sometimes surface
cells are separated from the deeper. Fungiform papillae have a
mushroom-like outline and are less numerous than the filiform papillae.
They have a narrow stalk and smooth-surfaced, dilated upper part. The
epithelium is thinner and nonkeratinized. The lingual muscle appears
as various sections of skeletal muscle bundles and is thick, Between
muscle bundles some small mixed lingual glands can been seen.
2.
Esophagus
1)
Material: Cross section of esophagus
2)
Stain: H.E.
3)
4)
Requirement: master the general structures of the digestive tract
and the structures of the esophagus.
Observation:
Naked eye: The lumen of the esophagus is irregular narrow space.
The epithelium lining the lumen is stained purple-blue. Beneath mucous
membrane there are light red-stained submucosa, two layers of
red-stained muscle. Adventitia is unclear.
Low power: Observe the structure from the lumen outward. According
to the type of tissue, the wall may be divided into 4 layers.
Mucosa: It is covered by nonkeratinized stratified squamous
epithelium. There are some lightly-stained round or irregular masses
in the epithelium. There are cross section of the papillae of lamina
propria. In some sections the lymphoid nodules and the ducts of
esophageal glands can be seen in the lamina propria. Note to observe
whether the esophageal cardiac glands located in the lamina propria
are present in this section. Muscular is mucosae is composed of a
thicker layer of longitudinal smooth muscle bundle in waves following
the plicae.
Submucosa: That consists of loose connective tissue with small
vessels, nerves, mucous acini of esophageal glands in it. (There are
no esophageal glands in some sections.) Sometimes nerve plexus can be
seen. The plexus consists of nerve fibers and nerve cells with a large
round pale-stained nucleus.
Muscle layer: It is rather thick and the muscle fibers are arranged
into inner circular and outer longitudinal muscle layer. Note the type
of muscle in the slide. Between the 2 muscle layers, the myenteric nerve
plexus can be found.
Adventita: That consists of loose connective tissue containing
nerves, blood vessel fat, cells etc.
3.
Fundus of stomach
1) Material: Cross section of fundus of stomach
2) Stain: H.E.
3) Requirement: Master the structures of stomach and identify the
chief cells and parietal cells of the gastric glands.
4) Observation:
Naked eye: The mucosa is stained in purple-blue. It projects into
the lumen forming folds. Under the mucosa are submucosa and muscle
layer. The Adventitia is unclear.
Low power:
Mucosa: The surface is lined by a simple columnar epithelium. The
cytoplasm contains adequate mucigen granules, so that the cells are
stained lightly. A transparent area is ptesent in the top of the cells.
The boundary of the cells is clear. The epithelium invaginates into
the lamina propria forming gastric pit. Under the epithelium is the
lamina propria which contains a great number of gastric glande. The
tubular glands may be present as longitudinal, oblique or cross
sections, occasionally, it may be found in the section that the gastric
glands communicate with the bottom of the pits. The museularis mucosae
is thinner, which is thinner, which is composed of an inner circular
and an outer longitudinal smooth muscle layer.
Submcosa: It consists of loose connective tissue.
Muscle layer: That is thicker and composed of an inner oblique,
a middle circular and an outer longitudinal smooth muscle layer. The
boundary between the inner oblique and middle circular smooth muscle
layer is obscure.
Serosa: It consists of a thin layer of loose connective tissue
covered by mesothlium.
High power: Observe the following carefully.
(1) The mucosa is lined by a simple columnar epithelium.
(2) The structure of gastric gland: It is composed of chief cells,
parietal cells. Mucous neck cells and endocrine cells. Mainly
identify the former two cells:
Chief cells: They are predominant in the body and the base of
the glands. The cells are columnar-shaped with basophilic
cytoplasm which contains the abundant rough endoplasmic reticulum
and with ovoid nuclei in the basal part of each epithelial cell.
Parietal cells: They are larger, round or pyramidal in form.
The cytoplasm is eosinophilic intensely. The cells are present
mainly in the neck and the body of the glands.
(3) The mesothelium of serosa is simple squamous epithelium.
4.
The pylorus
1)
Material: Longitudinal section of the pylorus
2)
Stain: H.E.
3)
Requirement: Compare it with the fundus of stomach.
4)
Observation:
Low power: The gastric pits are deeper than that in fundus. The
pylorus glands are mucous gland in the lamina propria and the glandular
epithelium is simple column in form. The cytoplasm is pale-stained.
The circular smooth muscle layer in the pylorus is thicker.
5.
Small intestine
1)
Material: Cross section of ileum
2)
Stain: H.E.
3)
Requirement:Master the structures of small intestine and the
structural characteristics of ileum.
4)
Observation
Low power:
Mucosa: There are a number of finger-like processes called villi
at the surface of the mucosa. The villi project into the lumen and
consist of epithelium and lamina propria. In sections, some villi are
cut off. The longitudinal, cross and oblique sections of villi are
present. There are many intestinal glands in the lamina propria. The
glands may out in various sections. In addition, aggregations of a
numerous lymphoid nodules form structures called Peyer’s patches,
which may project from lamina propria into submucosa, so that the
muscular is not intact.
Submucosa: It consists of loose connective tissue.
Muscle layer: That is composed of an inner circular and an outer
longitudinal smooth muscle layer.
Adventitia: It is fibrosa or serosa.
High power: Observe the following carefully.
(1)
The intestinal epithelium is simple columnar. There is the
striated border stained red and bright at the free surface of the
columnar cells. The vacuolar cells between the columnar epithelial
cells are goblet cells.
(2)
The lymph capillary in the core of the villi is called lacteal
which is lined by simple squamous epithelium. (Demonstration).
Around the lacteal the blood capillaries and some scattered
lontitudinal smooth muscle cells can be seen.
(3)
Intestinal glands: In H.E. sections, the columnar cells and
goblet cells of the intestinal glands can be seen, Paneth cells and
endocrine cells of intestine are shown in demonstration sections.
6.
Large intestine
1)
Material: Large intestine
2)
Stain: H.E.
3)
4)
Requirement: Master the structural characteristics of large
intestine and compare them with those of small intestine.
Observation:
Low power: There are folds but no villi in the large intestine, that
the mucosa has a comparatively smooth surface. The goblet cells between
the columnar cells are much more. In the lamina propria there are a
great number of intestinal glands. In some sections, it can be seen
that the smooth muscle fibers of the outer longitudinal layer gather
into three equidistant longitudinal bands known as taeniae coli. The
serosa may contain the adipose tissue that forms appendices
epiploicae.
7.
Appendix
1)
Material: Cross section of appendix
2)
Stain: H.E.
3)
Requirement: Compare it with large intestine
4)
Observation:
Naked eye: The lumen is small and irregular.
Low power: The general structure is similar to that of the large
intestine, but the intestinal glands are fewer and shorter. The
lymphatic tissue is much more abundant in the lamina propria. The
muscularis mucosae is often incomplete, because the lymphatic tissue
project into the submucosa. The boundary of lamina propria and
submucosa is obscure. The muscle layer is thinner. There are no
taeniaecoli and appendices epiploicae.
Sections for demonstration
1.
The taste buds
1)
Material: Vertical section of the root of tongue
2)
Stain: H.E.
3)
Requirement: Observe the taste buds, and distinguish the taste
cells and supporting cells.
4) Observation: The taste buds are mainly distributed in the
epithelium of the circumvallate papillae’s lateral wall surrounded
by a deep groove. They are ovoid bodies arranged perpendicular to the
epithelium. They consist of taste cells, supporting cells and basal
cells.
(1)
Taste cells: They are spindle-shaped with ovoid nuclei. Their
cytoplasm and nuclei are stained deeply. The taste hairs are
unclear.
(2)
Supporting cells: They are spindle-shaped and larger than
taste cells. Their cytoplasm and nuclei are stained pale.
2.
Oesophagogastric junction
1)
Material: Longitudinal section of the oesophagogastric junction
2)
Stain: H.E.
3)
Requirement: Understand the change of epithelium at the
oesophagogastric junction.
4)
Observation:
Low power: There is generally an abrupt change at the
oesophagogastric junction from stratified squamous epithelium lining
esophagus to the simple columnar epithelium that characterizes the
stomach. And the gastric pits are present.
3.
Paneth cells in intestinal glands
1)
Material: Small intestine
2)
Stain: H.E.
3) Requirement: Understand the morphological features of the paneth
cells.
4)
Observation: The cells are located in the bottoms of the intestinal
glands and arranged in groups of 3-5 cells. They are pyramidal in
shape.
Their nuclei are round and situated near the base of the cells.
The cells contain many acidophilic granules in their cytoplasm.
4. Endocrine cells in intestine
1)
Material: Small intestine
2)
Stain: Silver nitrate
3)
Requirement: Understand the features of the endocrine cells.
4) Observation: The granules in the basal cytoplasm are stained black
by using silver nitrate. In some cells the granules are so abundant that
their nuclei are covered.
Electron micrographs
1. Chief cells of the gastric glands
It shows three chief cells, among them the middle is an intact cell.
At upper right is a glandular cavity. There are a few microvilli at the
free surface of the chief cells and abundant rough endoplasmic reticulum
in the basal cytoplasm(ER). The apical cytoplasm contains numerous
zymogen granules(secretory granules, SG). The Golgi apparatus is
generally located just above the nucleus, but it is unclear in this
picture.
2. Parietal cells of the gastric glands
The middle in the photograph is a glandular cavity(L). At the below
is an intact parietal cell. The membrane of the apical cell surface
invaginates into the cytoplasm to form many intracellular canaliculi. (C).
The canaliculi are lined by numerous microvilli. There are a number of
larger mitochondria in the cytoplasm near the canaliculi. The smooth
endoplasmic reticulum in the photograph is obscure.
3. Gastric endocrine cells.
The middle in the photograph is a glandular cavity (1) surrounded by
many mucous cells (2) The endocrine cells (3) are between the mucous cells.
The cytoplasm contains argentophilic granules which generally occupy the
basal portion. The endocrine cell at the upper belongs to open-type cell.
Its free surface with a few microvilli may project to lumen. The endocrine
cell at the below belongs to close-type cell. Its top isn’t exposed to
the lumen.
4. Absorptive cells and goblet cells
At upper left is a goblet cell and the others are absorptive cells which
are tall column in shape and have ovoid nuclei located near the base of
cell. The luminal surface is composed of closely packed, regularly
arranged microvilli (MV) forming striated border with the light
microscope. The lateral cell surfaces form interdigitating processes. The
junctional complexes in this photograph are not obvious. The goblet cells
between the absorptive cells contain numerous mucigen granules in the
apical portion. The rough endoplasmic reticulum and Golgi apparatus are
in the deeper portion of the cell.