Anatomy-histology corelation.ppt by ZubairLatif


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									         GI tract
Anatomy-Histology Correlate

                       By: Michael Lu, Class of ‘07
- The digestive system allows us to ingest
and digest food, effectively adsorbing the
nutrients required for the normal functioning
of all body systems and expelling the
undigested waste products.
- The digestive tract is essentially a long
tube that begins from the oral cavity and
continues on to the esophagus, the
stomach, the small and large intestines, and
finally the anus. The pancreas, liver, and
gallbladder help with the digestion and
absorption of nutrients.
- Beginning with the oral cavity, we will first
look at the lips. There is a transition from
skin to oral mucosa at the vermillion
border (v.b.). The lip gets its red color from
the capillaries in the high dermal papillae
which are separated from the lip surface by
a thin layer of epidermis, as indicated by the
- The vermillion border lacks sweat glands
or sebaceous glands, making it susceptible
to chapping.
- The labial vestibule of the oral cavity is
lined by non-keratinized stratified
squamous epithelium. The glands found in
the underlying tissue are mostly mucus-
secreting with some mixed muco-serous
glands. The inner surface of the cheek is
essentially the same.
- The oral mucosa is composed of various types of epithelia. Non-keratinized
stratified squamous epithelium (blue) is present where flexibility is required,
as is the case of the lip and cheeks aforementioned.
- Keratinized stratified squamous epithelium (red) is required where
abrasion occurs frequently and the lining epithelium needs to be more rigid.
This is the case of the hard palate (bottom left) and the gingiva (next slide).
The keratinized epithelium, labeled as stratum corneum, is firmly attached to
the underlying bone.
- The soft palate (bottom right) is flexible and thus covered by non-keratinized
stratified squamous epithelium. There are numerous mucus-secreting glands
amongst the skeletal muscle within the underlying tissue.
- The remainder of the oral vestibule and the ventral surface of the tongue are
also covered by non-keratinized stratified squamous epithelium.
- The tongue, discussed later, contains specialized mucosa (orange) for the
special sense of taste.
- Top left panel: As the non-keratinized stratified
squamous epithelium (B) of the oral vestibule
approaches the teeth, a transition occurs at the muco-
gingival junction (C) into keratinized stratified
squamous epithelium (A) of the gingiva.
- The gingiva (bottom left) is very tightly attached to the
tooth by the dentogingival fibers. Free gingiva
surrounds the enamel, which was removed during slide
preparation (decalcification) leaving the dentin.
- The periodontal ligament is anchored within the
tooth cementum and inserts into the alveolar bone.
These insertions, indicated in the bottom right with an
arrow, are known as Sharpey’s fibers. The periodontal
ligament serves to attach the tooth to the bone and to
absorb shock.
- The enamel , which is 96% mineral, covers the crown
of the tooth. However, the dentin (80% mineral)is much
thicker and forms the majority of the tooth. The black
lines (top left) that run from the pulp cavity to the dento-
enamel junction are dentinal tubules that were filled
with odontoblasts during tooth growth.
- At the root of the tooth, the surface is covered by
cementum, which has a composition similar to bone.
The bottom left panel shows the cemento-enamel
junction (CEJ), where the enamel ends and cementum
begins. The granular dentin is also a good marker for
this junction.
- Note the acellular cementum near that CEJ and
compare it to the cellular cementum (bottom right)
near the root of the tooth.
- The tongue is specialized for moving food around in the oral
cavity and mostly composed of skeletal muscle. The ventral
surface is covered by non-keratinized stratified squamous
epithelium. The dorsal surface, shown on the left, is covered by
various papillae.
- The filiform papillae (bottom left) look like “hooks” that are
composed of hard keratinized epithelium.
- The fungiform papillae (bottom middle), easily identified, are
mushroom-shaped and slightly higher than surrounding filiform
papillae. To the naked eye, they appear as red spots on the tongue.
The paler staining regions are taste buds.
- The circumvallate papillae are much larger than fungiform
papillae, with numerous taste buds. In addition, they are
surrounded by deep trenches, which are continually flushed by
secretions from the underlying lingual (von Ebner’s) glands.
- Note the 3 major salivary glands. Below, from left to right,
are the parotid, submandibular, and sublingual glands.
- Parotid gland: In the parotid fossa, three main structures
transverse this gland – facial nerve, external carotid artery,
and retromandibular vein. The parotid duct opens near the
upper 2nd molar tooth. The gland is completely serous.
- Submandibular gland: Sitting most posteriorly in the
submandibular triangle, it is supplied by the facial artery and
vein. Submandibular ducts, which cross the lingual nerves,
open on both sides of the tongue frenulum. It is mostly serous
but partially mucus, with many serous demilune cells.
- Sublingual gland: The smallest salivary gland sits beneath
the oral mucosa in the floor of the mouth. It has multiple small
openings. This gland is almost completely mucus-secreting.
                                         - The intercalated duct carries the
                                         acinar secretion to the striated
                                         duct. Shown below, it is
                                         characterized by the faint vertical
                                         striations in the cytoplasm of the
                                         duct cells. They are elaborate
                                         membrane infoldings and aligned
                                         mitochondria, allowing the striated
                                         duct to pump sodium and chloride
                                         out of the lumen and exchanging for
                                         potassium and bicarbonate. As a
                                         result, the secretions become

- Within the salivary glands, the                                              - As a review – the parotid gland is
lobules are composed of numerous                                               completely serous, the
acini.                                                                         submandibular gland is mostly
                                                                               serous and partly mucous, and the
- Secretions produced by the acinar
                                                                               sublingual gland is mostly mucous.
cells are released into intralobular
ducts, which converge into larger                                              - In addition to the relative ratio of
ducts leading out of the salivary                                              serous acini to mucous acini, the
glands.                                                                        submandibular and sublingual
                                                                               glands are also characterized by its
- The panel above shows an
                                                                               serous demilunes. These are
intercalated duct lined with thin,
                                                                               serous cells capping mucous acini,
low cuboidal epithelium.
                                                                               indicated by the arrows in the panel
- Within the acini, the secretions are                                         above.
hypertonic. In the intercalated duct,
they are modified to be isotonic.
- The gastrointestinal tube is composed
of 4 distinct layers.
- A) The mucosa is the innermost layer
near the lumen of the GI tube. It is further
subdivided into 1) the epithelium, 2) the
lamina propria, and 3) the muscularis
mucosae. Depending on the location in the
GI tract, there may also be glandular tissue.
- B) The next layer is the submucosa,
which contains extensive connective tissue.
Only the esophagus and the duodenum
have secretory glands within the
- C) The third layer is the muscularis
propria or externa. As shown in the
diagram, there is an inner circular layer and
an outer longitudinal layer.
- D) The outermost layer is the serosa or
adventitia. The former refers to the visceral
layer of the peritoneum. The latter consists
of loose connective tissue.
- Note in the abdomen, the retroperitoneal
parts of the GI tract include the duodenum,
pancreas, ascending colon, descending
colon, and rectum, all with their own
fusion fascia. All other sections in the
peritoneum are attached via mesentery.
- The kidneys are also retroperitoneal.
- The pharynx connects the nasal and oral cavities
superiorly with the larynx and esophagus inferiorly. It
sorts food, water, and air to arrive at their destinations.
- In the pharynx, the paths of food and air cross. Food
travels from the mouth (anterior) to the esophagus
(posterior). Air travels from the choanae (posterior) to
the trachea (anterior).
- The pharynx contains 2 layers of muscles – outer
circular and inner longitudinal.
- The outer circular muscles include the superior,
middle, and inferior pharyngeal constrictor
muscles. One easy landmark to identify them is the tip
of the greater horn of the hyoid bone, to which the
middle pharyngeal constrictor attaches. The 3 muscles
contract serially to push a bolus down the esophagus.
- The inner longitudinal muscles include the
stylopharyngeus, salpingopharyngeus, and
palatopharyngeus muscles, which elevate and widen
the pharynx to accommodate a bolus when swallowing.
- The levator veli palatini and tensor veli palatini (not
shown here) muscles elevate the soft palate to seal off
the nasopharynx when swallowing. The epiglottis
closes off the larynx and trachea.
- The interior fascia is the pharyngobasilar fascia, an
area which does not have any muscle tissue.
- The pharyngeal mucosa is covered by non-
keratinized stratified squamous epithelium, with an
underlying dense layer of elastic tissue (blue brackets).
- The esophagus is posterior to the larynx and trachea
in the neck region and upper thorax. It travels on the
right side of the descending aorta, passes through the
diaphragm, and connects with the stomach.
- Note the esophageal plexus with the main anterior
and posterior vagal trunks from the left and right
vagus nerves, respectively. Within the submucosa is
the Meissner’s plexus and in between the muscular
layers is the myenteric or Auerbach’s plexus.
- The histological slides are good examples of the 4
layers of the GI tube. The epithelium (E) is non-
keratinized stratified squamous. The muscularis
mucosae (MM) is indicated by the arrows. There are
also inner circular and outer longitudinal muscle layers.
- The upper third is skeletal muscle (voluntary), middle
third is mixed, and lower third is smooth muscle

                       - IMPORTANT:
                       Remember, the
                       esophagus has secretory
                       glands in the
- Note that the esophagogastric junction is located
approximately at the level of the diaphragm.
Contractions of the diaphragm create sphincter-like
effects, preventing reflux of stomach acids and content.
The esophagogastric junction is a functional, not
anatomical, sphincter.

- Note the abrupt transition of epithelium at the
esophagogastric junction, from the non-keratinized
stratified squamous epithelium of the esophagus to the
columnar gastric surface epithelium.
- Once again, there is no evident muscular sphincter at
the junction.

- In the following slides, we will review the anatomical
features of the stomach, followed by a histological
comparison of the stomach mucosa.
- The stomach sits in the upper left quadrant of the abdomen. It can be divided into 4 parts: the cardia, the
fundus, the body or corpus, and the pylorus.
- The lesser curvature of the stomach is connected to the liver via the hepatogastric ligament, which comprise
the lesser omentum with the hepatoduodenal ligament. On the other side, the greater curvature is connected to
the greater omentum of the abdomen. Note the other surrounding structures.
- The venous drainage of the lesser curvature involves the left and right gastric veins, which anastomose as the
coronary vein. The greater curvature is drained by short gastric veins into the anastomoses of the left and
right gastro-omental veins. They all drain into the hepatic portal vein, hepatic veins, and inferior vena cava.
- The stomach is supplied by the arteries branching off
the celiac trunk.
- There are three major branches of the celiac trunk:
      - 1) left gastric artery – supplies the lesser
      curvature and anastomoses with the right gastric
      - 2) splenic artery – supplies the spleen, giving
      off the left gastro-omental artery which supplies
      the greater curvature and anastomoses with the
      right gastro-omental artery
      - 3) common hepatic artery – supplies the liver
      with the hepatic artery proper. The right gastric
      and right gastro-omental arteries both branch off
      the hepatic artery proper. In addition, it also gives
      off the gastroduodenal artery to supply the
      duodenum, pancreas, and greater curvature.

- In short, the stomach is supplied by the right and left
gastric arteries at the lesser curvature and the right and
left gastro-omental arteries at the greater curvature.
- The lesser curvature is drained by the coronary vein,
while the greater curvature is drained by the right and
left gastro-omental veins.
- The gastric mucosa and submucosa are folded into rugae.
- The stomach surface epithelium itself is also highly folded
forming gastric pits.
- Gastric glands empty into the bases of the gastric pits
(bottom left). The first part of the gastric gland contains
mostly parietal cells, which secrete HCl acid and intrinsic
factor. The bases of the glands contain mostly chief cells,
which secrete the enzyme pepsinogen.
- In addition, there are also enteroendocrine cells that
secrete gastrin, somatostatin, and other hormones into the
bloodstream and not the stomach lumen.
- Note the cardiac glands (gastric glands in the cardia; blue
box & bottom right) are mucus secreting, and the gastric pits
extend approximately half (50%) the depth of the mucosa.
-The gastric glands proper in the corpus and the
fundic glands in the fundus have the same structure.
Gastric pits only extend about 25% the mucosal depth.
- The surface epithelial cells are mucus-secreting, but
they are NOT goblet cells. The mucinogen granules do
not distort the round or oval nuclei sitting at the base.
- In the bottom left panel, some gastric pits are
indicated. In the gastric glands, the left bracket is the
parietal cell zone and on the right is the chief cell zone.
- The bottom right panel magnifies the base of a gastric
gland. The black arrows are parietal cells, which are
roughly oval to pyramidal in shape with a round, central
nucleus. The red arrowheads indicate chief cells, with
granular apical cytoplasm and empty granules.
- The gastric pits of the pyloric glands (bottom left &
blue box) extend at least half way to two-thirds down
the depth of the mucosa. The base of the gastric pits
are indicated by the vertical line with the arrow.
- The bottom right panel shows the gastroduodenal
junction. The thickened muscle mass, indicated by the
arrow, is the pyloric sphincter. Unlike the
esophagogastric junction, which is a functional
sphincter, the gastroduodenal junction is an anatomical
sphincter. The boxed region in the duodenum indicates
submucosal Brunner’s glands, which will be discussed
- As review, the mucosae of the cardia, body, and pylorus are compared. The vertical lines indicate the
approximate end of the gastric pit and start of the gastric gland.
- Note the paler staining of the cardiac and pyloric glands compared to the parietal and chief cells of the gastric
glands proper.
- Approximate pit depth: cardia – 50%; body – 25~33%; pylorus – 50~66%
- The duodenum is mostly retroperitoneal and divided
into 4 parts – the ampulla (no circular folds),
descending (papillae), horizontal (crossed by superior
mesenteric artery), and ascending (duodenojejunal
flexure and suspensory ligament) parts.
- The duodenum is supplied by anterior and posterior
superior pancreaticoduodenal arteries (celiac trunk) and
anterior and posterior inferior pancreaticoduodenal
arteries (superior mesenteric artery).
- The gastroduodenal junction (bottom left) connects
the stomach (S) with the duodenum (D). The muscular
pyloric sphincter and outer muscle layers are shown.
- A distinct characteristic of the duodenum, which differs
from the other parts of the small intestine, are mucus-
secreting Brunner’s glands (G) within the submucosa
(just like the esophagus).
- Another important characteristic of the small intestine
(in general) is the presence of numerous villi. These
finger-like projections extend out from the mucosal
surface into the intestinal lumen, increasing surface
area for absorption. The inset indicates permanent folds
in the intestinal wall known as plicae.
- The 4 layers of the GI tube are shown again in the
bottom right. The villi consist of epithelium and lamina
propria of the mucosa. The small arrows point to
muscularis mucosa. The submucosa, muscularis
externa, and serosa are also labeled.
- Note the arteries of the small intestine, all supplied by
the superior mesenteric artery off the aorta. Jejunal
arteries are shorter than ileal arteries. They
anastomose as arcades and give off arteriae rectae.
                              - Here we take a closer look at the intestinal villi. The villus core
                              contains loose connective tissue, smooth muscle from the
                              muscularis mucosae, blood vessels, lymphatic vessels, and nerves.
                              The blue arrowheads indicate intraepithelial lympthocytes.
                              Epithelial cells are shed at the villus tip, where they are shed or
                              - The epithelium consists of absorptive, columnar enterocytes and
                              goblet cells. The black arrowheads point to the apical surfaces of
                              enterocytes, forming a striated border. These are the thousands of
                              microvilli which increase surface area for absorption.
                              - At the base of intestinal crypts, we can find enteroendocrine
                              cells, which are identified by cytoplasmic granules at the basal
                              instead of apical surface, releasing hormones into the bloodstream.
                              - There are also Paneth cells that secrete lysozyme to kill bacteria.

A – goblet cell
B – enterocyte (absorptive)
C – Paneth cell
D – enteroendocrine cell
- Once again, the 4 layers of the GI tract are shown –
mucosa, submucosa, muscular layers, and serosa.
- The jejunum and ileum are attached to the posterior
abdominal wall via mesentery. Within the mesentery
are arcades and straight arteries. Jejunal arteries are
shorter than ileal arteries. In addition, the jejunum
mucosa has many more circular folds than the ileum,
showing that the jejunum absorbs most of the nutrients.
- Histologically, the jejunum and ileum are very similar.
Note once again the numerous villi. Extending into the
lamina propria from the mucosa are intestinal glands,
better known as intestinal crypts or crypts of
- REMEMBER: Only the esophagus and duodenum
have submucosal glands.
- The ileum ends in the right lower quadrant of the
abdomen and connects to the cecum, which then leads
into the ascending colon.
- The ileocecal region is supplied by the ileocolic
artery, which branches off the superior mesenteric
artery. The ileocolic artery gives off a colic branch
which supplies beginning of the ascending colon, and
an ileal branch that supplies the end of the ileum.
- Note the abrupt transition in the epithelial lining from
the small intestinal (S) villi to the glandular form of large
intestine (L). The ileocecal valve contains considerably
thickened muscularis propria (M) with some lymphoid
tissue (Ly).
- Note the appendix and appendicular artery shown
here. We look in more detail in two slides.
- Note the distinct structures of the large intestine – haustra,
omental appendages, and teniae coli (3 distinct bands of
longitudinal muscle). The colon can be divided into the cecum,
ascending, transverse, descending, and sigmoid colons, and
the rectum. The ascending and descending portions are
retroperitoneal; all other portions have their mesentery.
- The first third of the colon is supplied by the superior mesenteric
artery via the ileocolic, right colic, and middle colic arteries. The
rest of the colon is supplied by the left colic, sigmoid, and rectal
arteries all branching off the inferior mesenteric artery. Note also
the marginal artery running the colonic border and the arteriae
- Rule of thumb: all intestinal arteries should be identified by where
they are running to, not the order of which the branches come off.
- Note the main differences between colonic versus intestinal
epithelium: there are only glands, no villi, and more goblet cells.
- Generally, the appendix has the same histological
appearance as the large intestine. The main difference
is the appendix contains a complete outer layer of
longitudinal muscle, instead of bands of teniae coli.

- The mucosa resembles that of the colon. There is
simple columnar epithelium with numerous goblet cells.
The glands or crypts of Lieberkuhn are straight and
unbranched, but there are no villi.

- The border between mucosa and submucosa, or
namely the muscularis mucosae, may be difficult to
identify. The submucosa are often heavily infiltrated with
lymphoid follicles (F). The lymphoid tissue may even
extend into the mucosa, almost approaching the luminal

- The adventitia, or serosa (S), and mesoappendix (M)
are also indicated.
- The rectum differs from the rest of the colon in that the
lower one-third has nothing to do with the peritoneum,
and the upper two-thirds are considered retroperitoneal.
In addition, the teniae coli expand and unite to form the
longitudinal muscle layer.
- The external anal sphincter is composed of
voluntary, skeletal muscle. In contrast, the internal anal
sphincter is not under conscious control.
- Note the anal columns, between each are anal
valves. They mark the pectinate line, where there is
an abrupt transition from simple columnar epithelium
of intestine to keratinized stratified squamous
epithelium of skin.
- The pectinate line also divides arterial supply.
Superior to the line is supplied by the superior rectal
arteries and drained by superior rectal veins into the
portal system back to the liver. Inferior to the line, the
inferior rectal arteries supply blood and middle and
inferior rectal veins drain into the caval system to the
vena cava.
- Note the large number of veins in this region, which
may become dilated and varicose, commonly known as
hemorrhoids. External hemorrhoids occur below the
pectinate line and can be very painful. Internal
hemorrhoids, on the other hand, are usually painless.

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