HISTOLOGY OF HISTOLOGY OF GASTROINTESTINAL GASTROINTESTINAL

TRACTTRACT

ContentContent1. Introduction

2. General Structure

3. Histology of:1. Oral Cavity

2. Esophagus

3. Stomach3. Stomach

4. Small Intestine

5. Large Intestine

6. Appendix

7. Salivary Gland

8. Liver

9. Gall Bladder

10. Pancreas

4. Medical Application

IntroductionIntroductionGastrointestinal Tract

Digestive Tracts

Oral Cavity

Esophagus

Associated Glands

Salivary Glands

LiverEsophagus

Stomach

Small & Large Intestines

Rectum

Anus

Liver

Gall Bladder

Pancreas

General Structure of Digestive TractGeneral Structure of Digestive TractCommon Characteristics:

o Hollow tube composed of a lumen whose diameter varies.

o Surrounded by a wall made up of 4 principal layers:• Mucosa

o Epithelial lining; A lamina propria of loose connective tissues rich in blood, lymph vessels and smooth muscle cells; Muscularis mucosae.

• Submucosa• Submucosao Dense 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 CavityOral CavityStratified Squamous Epithelium

Keratinized

Protects Oral Mucosa

Non Keratinized

Covers soft palate, lips, Protects Oral Mucosa from damage during masticatory function.

In Gingiva and Hard Palate

Lamina Propria has several papillae and rest directly on bony tissue

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 CavityOral Cavity• Tongue

o Papillae

• Filiform

• Fungiform

• Foliate

• Circumvallate• Circumvallate

• Pharynx

• Teeth and Associate Structures

o Dentin

o Enamel

o Pulp

o Periodontium

TongueTongue• 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.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.

TongueTongue

Papillae of TonguePapillae of Tongue

Papillae of TonguePapillae of Tongue• Filiform Papillae

o Conical Shape

o Numerous and present over entire surface of tongue

o Their epithelium does not contain taste bud and is Keratinized.

• Fungiform Papillae

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

o Contain scattered taste buds on upper surfaces

o Irregularly interspersed among filiform papillae.

• Foliate Papillae

o Poorly developed in humans

o 2 or more parallel ridges and furrows on the dorsolateral surface of tongue

o Contain many taste buds

Papillae of TonguePapillae 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 papillae

o Great number of taste buds present along sides of these o 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 Lamina

o 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 BudTaste 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 CELLS• 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)

PharynxPharynx• 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.nasal cavity.

• Contains tonsils.

• Mucosa of pharynx also has many small mucous salivary glands in its lamina propria

• Compose of dense connective tissues.

Teeth & Associate Teeth & Associate StructuresStructures

Teeth & Associate StructuresTeeth & Associate Structures• Dentin

o Calcified tissue harder than bone (higher content of calcium salt (70% of dry weight)).

o Composed mainly type 1 collagen fibrils, glycosaminoglycans, phosphoproteins, phospholipids and calcium salts in form of hydroxyapatite crystals.

o Organic Matrix of dentin is secreted by odontoblasts (pulp cells that line internal surface of tooth.

• Enamelo Hardest component of human body

o 96% mineral, up to 1% organic material and 3% water.

o Inorganic component of enamel is mostly hydroxyapatite crystals

o Organic enamel matrix compose of at least 2 heterogeneous classes of protein (amelogenins and enamelins).

o Consists elongated rods or columns enamel rods (prisms) bonded together by interrod enamel.

o Enamel matrix is secreted by cells called ameloblasts

Teeth & Associate StructuresTeeth & Associate Structures• Pulp

o Loose connective tissue

o Main components are odontoblast, fibroblasts, thin collagen fibrils and a ground substance contains glycosaminoglycans

• Periodontiumo Cementum

• Cementocytes (cells with appearance of Osteocytes)

Nourishment from periodontal ligament• Nourishment from periodontal ligament

o Periodontal ligament

• Special types of connective tissues

• Fibers organized to support pressure exerted during mastication.

o Alveolar Bone

• Immature type of bone in which collagen fibers are not arranged in the typical lamellar pattern of adult bone.

o Gingiva

• Mucous membrane firmly bounded periosteum of maxillary and mandibular bones

• Composed of stratified squamous epithelium and lamina propriacontaining numerous connective tissue papillae.

EsophagusEsophagus

EsophagusEsophagus• 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.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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StomachStomach

StomachStomach• Mixed exocrine endocrine gland.

• Divides into 4 regions:o Cardia

o Fundus

o Bodyo Body

o Pylorus

• Fundus and body are identical in microscopic structure.

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

Gastric MucosaGastric 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.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.

GastroGastro--esophageal esophageal JunctionJunction

Stomach (Stomach (CardiaCardia))• 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.portion of esophagus.

Stomach (Fundus & Body)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 Isthmus

Necko Neck

o 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)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.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 IntestineSmall Intestine

Duodenum

Jejunum

Ileum

Small Small IntestineIntestine• 4 layers:

1. Mucosa

2. Submucosa

3. Muscularis externa

4. Serosa4. Serosa

• Surface area of small intestine increased by

1. Length of small intestine

2. Valves of Kerkring/ Plica Circularis

3. Villi

4. Microvilli

5. Cypts Of Lieberkuhn

Mucosa of Small IntestineMucosa of Small Intestine

Valves of Valves of KerkringKerkring• Also known as Plica

Circulares

• Permanent submucosalcircular folds

• Large, seen with naked eye

• Prominent in duodenum & • Prominent in duodenum & jejunum

• Less marked in ileum

• Significance:

o Increases surface area

o Slow down the passage of contents

VilliVilli• Central lacteal (lymphatic

vessel)

• Core capillaries

• Core of connective tissue

• Epithelial cells – Tall • Epithelial cells – Tall columnar with striated border

Crypt of Crypt of LieberkuhnLieberkuhn(Intestinal gland)(Intestinal gland)

• Invaginations of lining epithelium into lamina propria

• Wall of crypt is lined by the following cells:

1. Columnar cells 1. Columnar cells

2. Goblet cells

3. Undifferentiated stem cells

4. Paneth / Zymogen cells

5. Argentaffin cells

Crypt of Crypt of LieberkuhnLieberkuhn

• Absorptive columnar cells / Enterocytes

o Microvilli which give it a striated border appearanceappearance

• Goblet cells

o Secretes mucus

• Undifferenciated cells

o Actively multiply, move upwards give rise to other cells

Crypt of Crypt of LieberkuhnLieberkuhn• Paneth cells / Zymogen cells

o Seen in deeper parts of crypts

o rich in Zinc, secrete lysozyme that destroys bacteria

• Endocrine cells• Endocrine cells

o Seen near lower ends of crypts

o Argentaffin cells

o Entero-chromaffin cells

o APUD cells – secrete serotonin

Submucosa Submucosa of Small of Small IntestineIntestineIntestineIntestine

Brunner’s GlandBrunner’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.• 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’sPeyer’s PatchesPatches• Lymphoid Nodules.

• Present in ileum, more prominent in terminal ileum.

• In lamina propria and submucosasubmucosa

• Dome shaped area devoid of villi

• Instead of absorptive cells, its covering epithelium consist M cells.

Differences between duodenum, Differences between duodenum,

jejunum & ileumjejunum & ileumDuodenum Jejunum Ileum

Epithelium ColumnarStriated border Few goblet cells

ColumnarStriated border goblet cells+

Columnargoblet cells++

Villi Broad Tongue-shaped Few thin finger-Villi Broad Spatula ShapedClosely packed

Tongue-shapedDifferentheights

Few thin finger-shaped

Lamina Propria Crypts+No Peyer’spatches

Crypts+Diffuse infiltration of lymphocytesNo Peyer’spatches

Crypts+Peyer’s patches extend into submucosa

Submucosa Mucus secreting Brunner’s glands

Only connective tissues and blood vessels

Peyer’s patches

Large IntestineLarge 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• 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)

AppendixAppendix

• 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 IntestineSmall Vs Large Intestine

Small intestine Large intestine

Villi 1. Crypts shallow2. Goblet cells less

1. Absence of villi2. Crypts deeper,

More Goblet cellscells

Longitudinal muscle coat of muscularisexterna

1. Uniformly thick 1. Three bands of Taenia coli

Histology of Accessory Histology of Accessory Organs of GITOrgans of GITOrgans of GITOrgans of GIT

Salivary GlandSalivary 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 FeaturesGeneral Features• Serous cells

o Pyramidal in shape

o Broad base resting on basal lamina

o Narrow apical surface with short irregular microvilli facing lumen

o Secretory cells are joined together by junctional complex and usually form spherical mass of cells complex and usually form spherical mass of cells called acinus

• Mucous Cells

o Usually cuboidal to columnar

o Oval nuclei pressed towards bases of the cells

o Most often organized as tubules, consisting of cylindrical arrays of secretory cells surrounding a lumen.

General FeaturesGeneral Features• Duct System

o Intralobular ducts

• Intercalated Ducts

o Lined by Cuboidal Epithelial Cells

o Ability to differentiate into secretory or ductal cells

• Striate Ducts

o Radial striations seen to consist infoldings of basal plasma membrane with numerous elongated plasma membrane with numerous elongated mitochondria

o Drains into Interlobular Ducts

o 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.

CharacteristicsCharacteristics• 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.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 demilunesof Gianuzzi.

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

other major salivary gland

LiverLiver• 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 • 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 BladderGall 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.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

PancreasPancreas

• 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 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 ApplicationMedical 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.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.

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