Gi Correlates

8/13/2019 Gi Correlates

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GI tract

Anatomy-Histology Correlate

By: Michael Lu, Class of 07


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- 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 andcontinues 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 fromskin to oral mucosaat 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

bracket.

- The vermillion border lacks sweat glandsor sebaceous glands, making it susceptible

to chapping.

- The labial vestibuleof 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-serousglands. The inner surface of the cheek is

essentiall the same.


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- 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 tothe 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.


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- 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 keratinizedstratified

squamous epithelium (A) of the gingiva.

- The gingiva (bottom left) is very tightly attached to the

tooth by the dentogingivalfibers. Free gingivasurrounds the enamel, which was removed during slide

preparation (decalcification) leaving the dentin.

- The periodontal ligamentis anchored within the

tooth cementumand inserts into the alveolar bone.

These insertions, indicated in the bottom right with an

arrow, are known as Sharpeys fibers. The periodontal

ligament serves to attach the tooth to the bone and toabsorb shock.


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- 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 tubulesthat were filled

with odontoblasts during tooth growth.

- At the root of the tooth, the surface is covered bycementum, 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 cementumnear that CEJ and

compare it to the cellular cementum(bottom right)near the root of the tooth.


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- The tongueis 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 papillaeare much larger than fungiform

papillae, with numerous taste buds. In addition, they are

surrounded by deep trenches, which are continually flushed bysecretions from the underlying lingual (von Ebners) glands.


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- 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 glandfacial nerve, external carotid artery,

and retromandibular vein. The parotid duct opens near the

upper 2ndmolar tooth. The gland is completely serous.

- Submandibular gland: Sitting most posteriorly in thesubmandibular 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.


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- Within the salivary glands, the

lobules are composed of numerous

acini.

- Secretions produced by the acinar

cells are released into intralobular

ducts, which converge into largerducts leading out of the salivary

glands.

- The panel above shows an

intercalated ductlined with thin,

low cuboidal epithelium.

- Within the acini, the secretions are

hypertonic. In the intercalated duct,they are modified to be isotonic.

- As a reviewthe parotid gland is

completely serous, the

submandibular gland is mostly

serous and partly mucous, and the

sublingual gland is mostly mucous.

- In addition to the relative ratio ofserous acini to mucous acini, the

submandibular and sublingual

glands are also characterized by its

serous demilunes. These are

serous cells capping mucous acini,

indicated by the arrows in the panel

above.

- 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 elaboratemembrane 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

hypotonic.


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- 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 musclesouter

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 musclescontract 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 palatiniand tensor veli palatini(notshown here)muscleselevate 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 anunderlying dense layer of elastic tissue (blue brackets).


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- The esophagusis 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 plexuswith the main anterior

and posterior vagal trunksfrom the left and right

vagus nerves, respectively. Within the submucosa isthe Meissners plexusand in between the muscular

layers is the myentericor Auerbachs 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

(involuntary).

- IMPORTANT:Remember, the

esophagus has secretory

glands in the

submucosa.


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- Note that the esophagogastric junctionis 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 atthe junction.

- In the following slides, we will review the anatomical

features of the stomach, followed by a histological

comparison of the stomach mucosa.

O


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NOTE:

- The stomachsits in the upper left quadrant of the abdomen. It can be divided into 4 parts: the cardia, the

fundus, the bodyor corpus, and the pylorus.

- The lesser curvatureof 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 curvatureis connected to

the greater omentumof the abdomen. Note the other surrounding structures.

- The venous drainage of the lesser curvature involves the leftand right gastric veins, which anastomose as the

coronary vein. The greater curvature is drained by short gastric veinsinto the anastomoses of the leftand

right gastro-omental veins. They all drain into the hepatic portal vein, hepatic veins, and inferior vena cava.


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- The stomach is supplied by the arteries branching off

the celiac trunk.

- There are three major branches of the celiac trunk:

- 1) left gastric arterysupplies the lesser

curvature and anastomoses with the right gastricartery

- 2) splenic arterysupplies the spleen, giving

off the left gastro-omental arterywhich supplies

the greater curvature and anastomoses with the

right gastro-omental artery

- 3) common hepatic arterysupplies the liver

with the hepatic artery proper. The right gastricand right gastro-omental arteries both branch off

the hepatic artery proper. In addition, it also gives

off the gastroduodenal arteryto supply the

duodenum, pancreas, and greater curvature.

- In short, the stomach is supplied by the right and leftgastric 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.

Th t i d b f ld d i t


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- The gastric mucosa and submucosa are folded into rugae.

- The stomach surface epithelium itself is also highly folded

forming gastric pits.

- Gastric glandsempty 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 cellsthat

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 pitsextend approximately half (50%) the depth of the mucosa.

Th t i l d i th d th


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-The gastricglands properin the corpus and the

fundic glandsin 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 areindicated. 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.


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- 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 thearrow, 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 Brunners glands, which will be discussed

next.

As review the mucosae of the cardia body and pylorus are compared The vertical lines indicate the


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- 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: cardia50%; body25~33%; pylorus50~66%

The duodenum is mostly retroperitoneal and divided


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- The duodenumis mostly retroperitoneal and divided

into 4 partsthe 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) andanterior 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 Brunners glands(G) within the submucosa

(just like the esophagus).

Another important characteristic of the small intestine


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- 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 thebottom 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 arteryoff the aorta. Jejunal

arteriesare shorter than ileal arteries. They

anastomose as arcadesand give off arteriae rectae.

Here we take a closer look at the intestinal villi The villus core


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- 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

exfoliated.

- 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 cellsthat secrete lysozyme to kill bacteria.

Agoblet cell

Benterocyte (absorptive)

CPaneth cell

Denteroendocrine cell

- Once again the 4 layers of the GI tract are shown


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- Once again, the 4 layers of the GI tract are shown

mucosa, submucosa, muscular layers, and serosa.

- Thejejunum andileumare 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 cryptsor crypts of

Lieberkuhn.

- REMEMBER:Only the esophagus and duodenumhave submucosal glands.

- The ileum ends in the right lower quadrant of the


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- 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 branchthat 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 valvecontains considerably

thickened muscularis propria (M) with some lymphoid

tissue (Ly).

- Note the appendix and appendicular artery shownhere. We look in more detail in two slides.

- Note the distinct structures of the large intestine haustra


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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

arteriesall branching off the inferior mesenteric artery. Note also

the marginal arteryrunning the colonic border and the arteriae

rectae.

- 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.


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- Generally, the appendixhas 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 toidentify. The submucosa are often heavily infiltrated with

lymphoid follicles (F). The lymphoid tissue may even

extend into the mucosa, almost approaching the luminal

surface.

- The adventitia, or serosa (S), and mesoappendix (M)

are also indicated.


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- 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 sphincteris composed ofvoluntary, skeletal muscle. In contrast, the internal anal

sphincteris 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

epitheliumof skin.

- The pectinate line also divides arterial supply.

Superiorto the line is supplied by the superior rectal

arteriesand drained by superior rectal veinsinto the

portal systemback to the liver. Inferiorto the line, the

inferior rectal arteriessupply blood and middleand

inferior rectal veinsdrain into the caval systemto the

vena cava.

- Note the large number of veins in this region, which

may become dilated and varicose, commonly known as

hemorrhoids. External hemorrhoidsoccur below the

pectinate line and can be very painful. Internal

hemorrhoids, on the other hand, are usually painless.

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Gi Correlates