gastro lab manual

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Gastrointestinal Lab Manual

Histology

dr. Jan Tambayong, PHK

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Introduction

Students will work individually. Sit anywhere.

This lab manual contains instructions for each one of the GI

labs. Each student will be supplied with GI microscopic slides at

the beginning of each lab session.

Wear a white lab coat every time you enter the lab room.

Please return your microslides at the end of every lab. This lab manual is for your personal use only.

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Important Information on the Lab Exam

The Lab Exam will be a bell ringer exam.

There will be an integrated lab exam, called OSPE(Objective Structured Practical Exam) for each block,

consisting of disciplines involved in the same block (egAnatomy, Histology, Pathology, etc), usually consisting of 14or 15 stations.

Each station will have one first-order question and onesecond-order question.

Second-order questions will include: Specific features

Function

Your reasoning

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LABORATORY 1

Introduction to the Gastrointestinal System

The purpose of this session is to provide you with

an overview of the structure of the upper GI tract,

ie. Lips, esophagus and stomach.

Identify the similarities and differences between

gastric mucosa, small intestinal mucosa and

colonic mucosa.

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The Lips

When examining this microslide, you notice a

structure with rounded end, lined by stratified

squamous epithelium. One side is covered by skin,

with integument of skin like hair follicles,sebaceous glands; this part is the outer part of the

lips.

Adjacent to this is a curved part: red portion of

your lips. Beyond that is the inner part of the lips,

entirely composed of mucous epithelia.

Teeth development

With small magnification, find the part containing

tooth buds, showing the development of teeth.

Try to locate : Enamel/email : dark magenta colored

Dentin : pink colored

Predentin : slightly pink

Ameloblast : closer to enamel

Odontoblast : closer to dentin

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Sexy Lips


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Cleft Lips


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Deciduous teeth


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The Tongue

Notice the unique pattern of the muscles, like the

pattern of tikar. The orientation of the muscle

fibers are in three directions: horizontal, transverse

and vertical, in accordance with its function.

Circumvallate Papillae

Observe the surface of the tongue. Youll find a

large rounded structure, most of which are

embedded beneath the tongue surface. This

structure, the circumvallate papillae, is surrounded

by a deep groove, lined by stratified epithelia which

contains small rounded structures, the taste buds, at

its periphery wall. Beneath the groove are serous

glands, the Ebners gland, which drain their contents

into the groove.

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Foliate Papillae

Observe the surface of the tongue. Youll see a series

of parallel ridges and furrows, the foliate papillae.

They are located at the dorsolateral surface of the

tongue.

Fungiform Papillae

Observe the surface of the tongue. Youll find a

mushroom-like structure, the fungiform papillae,

bulging above the tongue surface. Next to this

structure are situated rows of filiform papillae, which

have an elongated, conical structure. Its upper

surface contains scattered taste buds.

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Lingual Tonsil

At the base of the tongue youll see clusters of

solitary lymphnodules. It is covered by stratified

squamous epithelium.

Palatine Tonsil

Located at the lateral walls of the oropharynx,

youll find a pair of lymphoid organs, the palatine

tonsils. They are lined with a squamous stratified

epithelium, that often becomes so densely

infiltrated by lymphocyres that it may be difficultto recognize the real feature of this epithelium.

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The Esophagus

This photomicrograph is from the lower third of the

esophagus. It is lined with stratified squamous

epithelium. The muscularis mucosae is very thick.

The muscular layer, the muscularis externa,

consists of smooth muscle cells. The muscularisexterna of the mid portion of the esophagus

consists of a mixture of striated and smooth

muscle cells. In the upper part of the esophagus, it

is striated muscle.

Esophageal-cardiac junction

Observe the epithelial lining. At the esophageal-

cardiac junction, the epithelium from the

esophagus, stratified squamous epithelium, is

directly transformed into epithelium of the

stomach, simple columnar epithelium.

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Layers of GI tract


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Stomach


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Fundus

Gaster


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The stomach, a dilated segment of the digestive

tract, is divided into 4 regions: cardia, fundus,

corpus, and pylorus. The fundus and corpus are

identical in microscopic structure.

This photomicrograph is of the fundus gaster. The

simple columnar surface epithelium is invaginatedto form gastric pits (foveola gastrica). These pits

extent to 1/5 of the mucosa thickness into the

lamina propria.

Cells of the surface epithelium secrete an alkaline

mucus, forming a thick gel layer, that protects

them from the strong acid.

At the base of the gastric pits open several

branched tubular gastric (fundic) glands. The neck

of the gland consists of stem, mucous neck and

parietal (oxyntic) cells. The base of the gland

contains parietal, zymogenic (chief) and

enteroendocrine cells.

Note the large acidophilic cells; these are the

parietal cells of the fundus gaster, which secrete

HCl and an intrinsic factor for the absorption ofvit. B12

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Pilorus gaster

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LABORATORY 2

Identify the histological characteristic

appearance of the gastrointestinal tract from

the stomach to the recto-anal junction, ie.

duodenum, jejunum, ileum, colon, appendix,and recto-anal junction.

Identify histological features of small and large

intestines.

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Pylorus gaster.

The surface epithelium form deep gastric pits,

reaching of the mucosa thickness.

The glands are short and coiled, consisting of mucus

secreting cells.

Gastrin (G) cells which release gastrin, are intercalated

among the mucous cells. Gastrin stimulates the

secretion of acid (HCl) by the parietal cells

Enteroendocrine (D ) cells secrete somatostatin, which

inhibits the release of other hormones, including

gastrin.

The Small Intestine

The lining of the small intestine shows a series of

permanent folds, plicae circulares (Kerckring),

consisting of mucosa and submucosa, having a

semilunar, circular or spiral form. Besides that there

are outgrowth of the mucosa, forming intestinal villi,

consisting of epithelium and lamina propria.

This photomicrograph shows many cross-sections of

intestinal villi; plica is not seen here. These cross-

sections consist of absorptive, tall columnar cells ,

interspersed with mucus-secreting goblet cells , and

lamina propria.

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The duodenum

In the duodenum, the intestinal villi are leaf-

shaped. Plica Kerckring, if any, is very short.

In the submucosa are clusters of coiled, tubular

glands, Brunners gland. They may extent intothe lamina propria. Their cells are of mucous

type; their product is alkaline and acts to

protect the duodenal mucous membrane

against the effects of acid gastric juice.

Jejunum

In this segment of the digestive tract, the plicae

circulares Kerckring are the most developed,

containing many intestinal villi.

At the basal portion of the intestinal glands (also

called crypts of Lieberkhn), are exocrine cellswith large eosinophilic granules in their apical

cytoplasm; these are the Paneth cells. The

granules contain lysozyme, with antibacterial

activity.

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Ileum

This segment of the digestive tract containsintestinal villi, sometimes part of a plicaKerckring.

In the lamina propria and submucosa areaggregates of lymphoid nodules known as Peyers

patches (plaque Peyer). Each patch contains 10 to 200 nodules and is

visible to the naked eye as oval areas on the anti-mesenteric side of the intestine; they are devoidof villi. There are about 30 patches in the human.

Instead of absorptive cells, its coveringepithelium consists of M cells.

Colon

The colon, or large intestine, consists of a mucousmembrane with no folds or villi.

The intestinal glands are long and characterizedby a great abundance of goblet and absorptivecells, and a small number of enteroendocrine

cells. The muscularis layer have fibers of theouter longitudinal layer congregated into 3 thicklongitudinal bands called teniae coli.

In the anal region the mucous membrane forms aseries of longitudinal folds, the rectal columns ofMorgagni.

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Appendix

The appendix, an evagination of the cecum, ischaracterized by a relatively small, narrow, andirregular lumen, that is caused by the presence ofabundant lymphoid follicles in its wall.

It contains fewer and shorter intestinal glandsand has no villi or teniae coli.

The recto-anal junction

About 2 cm above the anal opening, theintestinal mucosa lining from simple columnar(rectum) is gradually replaced by stratifiedsquamous epithelium (anal eepithelium).

In this region the lamina propria contains aplexus of large veins that, excessively dilated andvaricose, produce hemorrhoid.

The muscular layer is not complete, because onlythe circular layer persists, its end forming theinternal sphincter ani muscle.

Surrounding the internal sphincter ani muscle isthe external sphincter ani muscle, consisting ofclusters of striated muscle fibers.

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LABORATORY 3

Identify the essential histological features of

the salivary glands and the liver, with special

reference to the organization of parenchyma

and stroma.

Identify the organization of the bile canaliculi,

space of Disse, liver sinusoid and Kupffer cells.

Identify the histology and vascular relations of

a classic hepatic lobule.

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Parotid Gland

It is a branched acinar gland; its excretoryportion is composed exclusively of serous cells.

As in other large salivary glands, the connectivetissue contains many plasma cells andlymphocutes. The plasma cells secrete IgA which

forms a complex with a secretory componentsynthesized by the serous acinar, intercalatedduct, and striated duct (intralobular duct) cells.This complex constitutes an immunologicdefence mechanism against pathogens in theoral cavity.

Submandibular (submaxillary) Gland

It is a branched tubuloacinar gland; its secretoryportion contains both mucous and serous cells.The serous cells are the main component of thisgland (90%).

The presence of extensive lateral and basal

membrane infoldings toward the vascular bedincreases the ion-transporting surface area 60times. Because of this, the cell boundaries areindistinct.

The cells that form the demilunes secrete theenzyme lysozyme, which main activity is tohydrolyze the walls of certain bacteria.

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Sublingual Gland

Like the submandibular gland, this gland is a

branched tubuloacinar gland formed of serous and

mucous cells. Mucous cells predominate in this

gland; serous cells are present exclusively on

demilunes of mucous tubules.

As in the submandibular gland, cells that form the

demilunes in this gland secrete lysozyme.

The duct system of the salivary glands are

intercalated ducts (lined by squamous to low

cuboidal cells), striated (intralobular) ducts (lined

by cuboidal cells with a lot of cytoplasm), and

larger interlobular ducts (lined by striated or

columnar cells around a large lumen).

In this photomicrograph is shown interlobularducts, with its large lumen, surrounded by

connective tissue.

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Liver

The liver is the organ in which nutrients absorbed

in the digestive tract are processed and stored for

use.

Most of its blood (70-80%) comes from the portal

vein; the smaller percentage is supplied by thehepatic artery.

In light microscopic sections, structural units

called liver lobules can be seen. In certain animals,

eg pigs, the lobules are separated from each

other by a layer of connective tissue. This is not

the case in humans.

In the lobule, the hepatocytes are radially

disposed in plates, directed from its periphery to

its center. The space between those plates

contains capillaries, the liver sinusoids.

In addition to the endothelial cells, the sinusoids

contain macrophages known as Kupffer cells, on

the luminal surface of the endothelial cells. Their

main functions are to metabolize aged

erythrocytes, digest hemoglobin, secrete proteinsrelated to immunologic processes and destroy

bacteria that enter blood through the large

intestine.

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LABORATORY 4

Identify the microscopic structure of the

pancreatic gland, the exocrine and the

endocrine portion of the gland.

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Pancreas

It is a mixed exocrine-endocrine gland that

produces digestive enzymes and hormones.

The enzymes are stored and released by cells of

the exocrine portion, arranged in acini. The

hormones are synthesized in clusters of endocrineepithelial cells, known as islets of Langerhans.

The exocrine portion of the pancreas is similar in

structure to the parotid gland (serous cells).

The distinction between the two glands can be

made based on the absence of striated ducts and

the presence of islets of Langerhans in pancreas.

Another characteristic detail is that in the

pancreas the initial portion of intercalated ducts

penetrate the lumen of the acini.

Nuclei, surrounded by a pale cytoplasm, belong to

the so called centroacinar cells, that constitute the

intra-acinar portion of the intercalated duct.

Intercalated ducts are tributaries of largerinterlobular ducts lined by columnar epithelium.

There are no striated ducts in the pancreatic duct

system.

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