HISTOLOGY OF GASTROINTESTINA

L TRACT

By: Gan Quan Fu, PT, MSc Anatomy (Batch 3)

Content1. Introduction2. General Structure3. Histology of:

1. Oral Cavity2. Esophagus3. Stomach4. Small Intestine5. Large Intestine6. Appendix7. Salivary Gland8. Liver9. Gall Bladder10. Pancreas

4. Medical Application

IntroductionGastrointestinal Tract

Digestive Tracts

Oral Cavity

Esophagus

Stomach

Small & Large Intestines

Rectum

Anus

Associated Glands

Salivary Glands

Liver

Gall Bladder

Pancreas

General Structure of Digestive Tract

Common Characteristics:o Hollow tube composed of a lumen whose diameter

varies.o Surrounded by a wall made up of 4 principal layers:

• Mucosao Epithelial lining; A lamina propria of loose

connective tissues rich in blood, lymph vessels and smooth muscle cells; Muscularis mucosae.

• SubmucosaoDense connective tissues with many blood and

lymph vessels.• Muscularis

o Contains smooth muscle cells, divide into 2 layers; internal (circular); external (longitudinal)

• Serosao Thin layer of loose connective tissue rich in blood

and lymph vessels and adipose and single squamous covering epithelium (mesothelium)

Oral CavityStratified Squamous Epithelium

Keratinized

Protects Oral Mucosa from damage during masticatory function.

In Gingiva and Hard Palate

Lamina Propria has several papillae and rest directly on bony

tissue

Non Keratinized

Covers soft palate, lips, cheeks and floor of

mouth

Lamina Propria has Papillae, similar to

those in dermis of skin and continuous with

submucosa containing diffuse small salivary

gland

Oral Cavity• Tongue

o Papillae• Filiform• Fungiform• Foliate• Circumvallate

• Pharynx• Teeth and Associate Structures

o Dentino Enamelo Pulpo Periodontium

Tongue• Mass of striated muscle covered by a mucous

membrane.• Muscle fibers cross on another in 3 planes, they

are grouped in bundles, usually separated by connective tissue.

• Dorsal Surface Irregular; Thicker epithelium; Covered anteriorly by a great number of small eminences papillae; Separated from anterior two thirds by a V-shaped boundary.

• Ventral Surface Epithelium on this surface is thinner.

Tongue

Papillae of Tongue

Papillae of Tongue• Filiform Papillae

o Conical Shapeo Numerous and present over entire surface of tongueo Their epithelium does not contain taste bud and is

Keratinized.• Fungiform Papillae

o Resemble mushrooms (narrow stalk and smooth surface, dilated upper part)

o Contain scattered taste buds on upper surfaceso Irregularly interspersed among filiform papillae.

• Foliate Papillaeo Poorly developed in humanso 2 or more parallel ridges and furrows on the

dorsolateral surface of tongueo Contain many taste buds

Papillae of Tongue• Circumvallate Papillae

o 7 – 12 extremely large circular papillae whose flattened surface extend above other papillae (Papillae surrounded by deep circular furrows).

o Distribute in the V region at the junction of the anterior 2/3rd and posterior 1/3rd of tongue.

o The epithelium is smooth on the lateral surface of papillaeo Great number of taste buds present along sides of these

papillae.• Taste Buds

o Onion shaped structures containing 50 – 100 cells.o Rests in Basal Laminao Apical portion project microvilli that poke through an

opening called taste pore.o 2types of cells are distinguished in relation to taste buds

• Supporting or sustentacular cells• Neuroepithelial or gustatory cells

Taste Bud• SUSTENTACULAR OR SUPPORTING CELLS

o Arranged peripherally, curved course, narrow at each end and broader in the centre appearing spindle shaped.

o At both ends the cells surround small openings known as external and internal pores.

• NEUROEPITHELIAL OR GUSTATORY CELLSo Distributed between the sustentacular cells long narrow,

having slender red shaped form with a nucleus in the middle.

o On the free surface, these cells gives rise to short hair which project into the lumen of the pit.

o The substances to be tasted gets dissolved in the saliva, stimulate the hairs in the neuroepithelial cells and the impulses is conducted along the nerves (sweet, bitter, sour, salty)

Pharynx• Lined by Stratified non keratinized squamous

epithelium in region continuous with esophagus.• Lined by ciliated pseudostratified columnar

epithelium containing goblet cells in region close to nasal cavity.

• Contains tonsils.• Mucosa of pharynx also has many small mucous

salivary glands in its lamina propria• Compose of dense connective tissues.

Esophagus

Esophagus• Muscular Tube function to transport food stuffs from

mouth to stomach• Covered by non keratinized stratified squamous

epithelium.• In general same layers as rest of digestive tract.• In submucosa groups of small mucous secreting glands

(esophageal glands) secretion facilitated transport of food stuff and protects mucosa.

• Lamina Propria near stomach groups of gland (esophageal cardiac gland) secrete mucus

• Distal end muscular layer Only smooth muscle• Mid Portion Mixture of striated and smooth muscle• Proximal end Only striated muscle cells• Portion in peritoneal cavity covered by serosa• The other portion covered by layer of connective tissue,

adventitia that blends into surrounding tissue.

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Stomach

Stomach• Mixed exocrine endocrine gland.• Divides into 4 regions:

o Cardiao Funduso Bodyo Pylorus

• Fundus and body are identical in microscopic structure.

• Mucosa and submucosa of undistended stomach lie in longitudinally directed folds known as rugae.

Gastric Mucosa• Consists surface epithelium invaginates to

various extend into lamina propria forming gastric pits.

• Lamina propria of stomach composed of loose connective tissue interspersed with smooth muscle and lymphoid cells.

• Muscularis mucosae to separate mucosa from underlying submucosa

• Epithelium lining the pits and covering the surfaces are simple columnar epithelium & all cells secrete alkaline mucus.

Gastro-esophageal Junction

Stomach (Cardia)• Mucosa contains simple or branched tubular

cardiac glands• Terminal portion of these glands are frequently

coiled, often with large lumens.• Similar in structure to cardiac glands of the

terminal portion of esophagus.

Stomach (Fundus & Body)

• Simple columnar surface epithelium extends into gastric pits into which opens into gastric glands.

• Lamina propria consist of fine reticular and collagen fibres fills the spaces between the packed gastric glands.

• Each gastric gland has 3 distinct region:o Isthmuso Necko Base

• Isthmus contains differentiating mucous cells and undifferentiated stem cells and parietal cells.

• Neck consist of stem, mucous neck and parietal cells.• Base contains parietal and chief (zymogenia) cells. • The muscularis mucosa composed of inner circular and

outer longitudinal smooth muscle.

Stomach (Pylorus)• Deep gastric pits into which the branched tubular

pyloric glands open.• The epithelium of the mucous membrane consist of tall

columnar cells which lines the deep pits and short glands.

• Longer pits and shorter coiled secretory portion compare to glands in cardiac region.

• The acini of pyloric glands and their ducts are in lamina prorpia.

• G (Gastrin) cells are enteroendocrine cells intercalated among mucous cells of pyloric glands.

• D cells secrete Somatostatin• The muscularis externa is made up of thick circular

muscle to form pyloric sphincter which helps to control emptying of the stomach.

Small Intestine

Duodenum

Jejunum

Ileum

Small Intestine• 4 layers:

1. Mucosa2. Submucosa3. Muscularis externa 4. Serosa

• Surface area of small intestine increased by1. Length of small intestine2. Valves of Kerkring/ Plica Circularis3. Villi4. Microvilli 5. Cypts Of Lieberkuhn

Mucosa of Small Intestine

Valves of Kerkring • Also known as Plica

Circulares• Permanent submucosal

circular folds • Large, seen with naked

eye• Prominent in duodenum &

jejunum• Less marked in ileum• Significance:

o Increases surface area o Slow down the passage

of contents

Villi• Central lacteal (lymphatic

vessel)• Core capillaries • Core of connective tissue• Epithelial cells – Tall

columnar with striated border

Crypt of Lieberkuhn (Intestinal gland)

• Invaginations of lining epithelium into lamina propria

• Wall of crypt is lined by the following cells:1. Columnar cells 2. Goblet cells3. Undifferentiated

stem cells4. Paneth / Zymogen

cells5. Argentaffin cells

Crypt of Lieberkuhn • Absorptive columnar

cells / Enterocyteso Microvilli which give

it a striated border appearance

• Goblet cells o Secretes mucus

• Undifferenciated cellso Actively multiply,

move upwards give rise to other cells

Crypt of Lieberkuhn • Paneth cells / Zymogen cells

o Seen in deeper parts of crypts o rich in Zinc, secrete lysozyme that destroys

bacteria • Endocrine cells

o Seen near lower ends of cryptso Argentaffin cellso Entero-chromaffin cells o APUD cells – secrete serotonin

Submucosa of Small Intestine

Brunner’s Gland

• In duodenum (Also known as duodenal glands)• Clusters of ramified, coiled tubular glands that

opens into the intestinal crypts.• Cells are mucous type.• Secretions are distinctly alkaline (PH8.1 – 9.3), to

protect duodenal mucous membrane from effects of acid gastric juice and to brings intestinal contents to optimum PH for pancreatic enzyme action.

Peyer’s Patches• Lymphoid Nodules.• Present in ileum, more

prominent in terminal ileum.• In lamina propria and

submucosa• Dome shaped area devoid of

villi• Instead of absorptive cells,

its covering epithelium consist M cells.

Differences between duodenum, jejunum & ileum

Duodenum Jejunum Ileum

Epithelium ColumnarStriated border Few goblet cells

ColumnarStriated border goblet cells+

Columnargoblet cells++

Villi Broad Spatula ShapedClosely packed

Tongue-shapedDifferent heights

Few thin finger-shaped

Lamina Propria

Crypts+No Peyer’s patches

Crypts+Diffuse infiltration of lymphocytesNo Peyer’s patches

Crypts+Peyer’s patches extend into submucosa

Submucosa Mucus secreting Brunner’s glands

Only connective tissues and blood vessels

Peyer’s patches

Large Intestine

• Consists mucosal membrane with no folds except in its distal (rectal) portion.

• No vili are present• Long intestinal glands • Great abundance of goblet and absorptive cells• Small number of enteroendocrine cells.• Fibers of outer longitudinal layer congregates in 3

thick longitudinal band (Teniae coli).• Serous layer characterized by small, pendulous

protuberances composed adipose tissues (appendices epiploicae)

• Mucous membrane forms a series of longitudinal folds (rectal columns of morgagni)

Appendix

• Evagination of cecum• Small, narrow and irregular lumen caused by

presence of abundant lymphoid follicles in its wall.

• Although general structure similar to large intestine, it contains fewer and shorter intestinal glands and has no teniae coli.

Small Vs Large Intestine

Small intestine Large intestine

Villi 1. Crypts shallow2. Goblet cells less

1. Absence of villi

2. Crypts deeper, More Goblet cells

Longitudinal muscle coat of muscularis externa

1. Uniformly thick 1. Three bands of Taenia coli

Histology of Accessory Organs of GIT

Salivary Gland3 pairs of salivary glands:

1. PAROTID GLAND• Purely serous (few mucous acini maybe

present)

2. SUBMANDIBULAR GLAND• Mixed, Predominantly serous

3. SUBLINGUAL GLAND• Mixed, Predominantly mucous

General Features• Serous cells

o Pyramidal in shapeo Broad base resting on basal laminao Narrow apical surface with short irregular microvilli

facing lumeno Secretory cells are joined together by junctional

complex and usually form spherical mass of cells called acinus

• Mucous Cellso Usually cuboidal to columnaro Oval nuclei pressed towards bases of the cellso Most often organized as tubules, consisting of

cylindrical arrays of secretory cells surrounding a lumen.

General Features• Duct System

o Intralobular ducts• Intercalated Ducts

o Lined by Cuboidal Epithelial Cellso Ability to differentiate into secretory or ductal cells

• Striate Ductso Radial striations seen to consist infoldings of basal

plasma membrane with numerous elongated mitochondria

o Drains into Interlobular Ductso Interlobular Ducts (Excretory Ducts)

• Initially lined with pseudo stratified or stratified cuboidal epithelium.

• Distal parts lined with stratified columnar epithelium consisting few mucus secreting cells

• Ultimately empties into oral cavity and lined by nonkeratinized-stratified squamous epithelium.

Characteristics• Parotid Gland

o Branched acinar glandso Surrounded by a capsule from which arise numerous

interlobular connective tissue septa that subdivides the gland into many lobes and lobules.

o Located in the connective tissue septa between the lobules are arteriole, venule and interlobular excretory ducts.

• Submandibular Glando Presence of both serous and mucous acini.o Mucous acinus are larger than the serous.o Between the mucous cells and basement membrane are

half moon shaped granules known as demilunes of Gianuzzi.

• Sublingual Glando Similar as Sub mandibularo Intralobular ducts are not as well developed as in other

major salivary gland

Liver• Repeating hepatic lobules (Hexagonal Unit).• Central Vein in the centre of each hepatic lobule.• Portal canals (Portal Traids) in periphery the

surrounding connective tissue [Branches of the hepatic artery, hepatic portal vein, bile duct, and lymph vessels seen.]

• Hepatic sinusoids (dilated blood channels) contains epithelial cells and macrophages called “Kupffer cells”

• The hepatic sinusoids separated from the underlying hepatocytes by subendothelial perisinusoidal space of Disse.

• The major exocrine functions of hepatocytes is synthesis and release about 500-1200ml of bile per day which is delivered to the gallbladder via the bile canaliculli.

Gall Bladder• It consist of mucosa composed of Simple

columnar epithelium and lamina propria; a layer of smooth muscle; a perimuscular connective tissue layer and a serous membrane.

• Mucosa has abundant folds that are particularly evident when gall bladder is empty.

• Epithelial cells are rich in mitochondria• Surrounding the bundle of smooth muscle fibres

is a thick dense connective tissue containing large blood vessels artery & vein, lymphatic and nerves.

• Serosa covers entire unattached gallbladder surface

Pancreas• Mixed endocrine and exocrine gland• Exocrine compound acinar gland, similar in

structure to parotid gland.• Distinction between 2 glands can be made based

on absence of striated ducts and presence of islets of Langerhans.

• Initial portions of intercalated ducts penetrate lumens of acini.

• Centroacinar cells constitude interacinar portion of intercalated duct.

Medical Application• Gastroesophageal Reflux Disease associated with

incompetent barriers at gastroesophageal junction caused by decrease in lower esophageal sphincter tone or hiatus hernia. Reflux esophagitis develops when mucosal defenses are not sufficient to protect esophageal mucosa from acid, pepsin and bile.

• Stress, ingested aspirin, NSAID or ethanol can disrupt epithelial layer in stomach lead to ulceration. Ulcer is disruption of mucosal integrity leading to an excavation due to active inflammation. Apirin and ethanol irritates mucosa partly by reducing blood flow.

References• Junquiera, L. C. (2005) Basic Histology text &

Atlas, 11th edn. McGraw Hill, New York.

Thank You