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Histology of upper GIT

Dr. Lutfun Nahar

GIT 311

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Contents

Oral cavityTongueEsophagusStomach

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IntroductionGastrointestinal tract is

a long , hollow tube or tract

Extends from oral cavity to anus

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General structure of GIT

Consists of four layers:

Mucous layerSubmucous layerMuscular layerSerous layer

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Mucous layer

Mucosa comprises:Epithelial lining

Lamina propria Consists of loose connective tissue

rich in blood and lymph vessels

Muscularis mucosae Consists of inner circular layer and an

outer longitudinal layer of smooth muscle cells

It separates the mucosa from the submucosa

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Function of mucosaSecretionAbsorptionBarrierImmunologic protection

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Submucous layer

Composed of dense irregular connective tissue and contains:

blood and lymph vessels submucosal or Meissner’s nerve plexus glands and lymphoid tissue

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Muscular layer

It contains smooth muscle cells that are spirally oriented and divided into two sublayers:

Internal sublayer is circular

External sublayer is longitudinal

Myenteric or Auerbach’s nerve plexus lies between two muscle sublayers

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Serous layer

Consists of thin layer of loose connective tissue

Rich in blood and lymph vessels, and adipose tissue

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Oral cavityOral cavity is lined with stratified squamous epithelium,

keratinized or nonkeratinized, depending on the region

The keratin layer protects the oral mucosa from damage during masticatory function

The keratin layer is present in the gingiva and hard palate

Nonkeratinized stratified squamous epithelium covers the soft palate, lips, checks and the floor of the mouth

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TongueThe tongue is a mass of striated muscle covered by a

mucous membrane

The dorsal surface of tongue is rough due to presence of papillae

The ventral surface of tongue is smooth

The posterior one-third of dorsal surface is separated from the anterior two-thirds by a V-shaped boundary

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Papillae Papillae are elevations of epithelium and lamina

propria. There are four types of papillae:

Filiform papillae - slender, conical shape, most numerous, cover the entire dorsal surface

Fungiform papillae - less numerous, have broad round surface resemble mushrooms

Foliate papillae – poorly developed in humans

Circumvallate papillae – large circular papillae with flattened surfaces, distributed in the V region in the posterior portion of the tongue

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Tongue: circumvalate papillae

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Muscles of tongue (Anterior part of tongue)

The tongue consists of criss-crossing bundles of skeletal muscle

The muscles are longitudinal, transverse or oblique

The connective tissue around the muscle bundle contain blood vessel

Anterior lingual gland – lies in the lower half of the tongue and opens on the ventral surface of the tongue

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Anterior region of the tongue

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Posterior tongue behind circumvallate papilla

Dorsal surface of posterior region exhibits large mucosal ridges

Nonkeratinized stratified squamous epithelium covers the mucosal ridges

Lamina propria of the mucosa is wider but similar to that in the anterior two-thirds

Lamina propria contains diffuse lymphatic tissue, accumulation of adipose tissue, nerve fibers and blood vessels

Skeletal muscle lies beneath the lamina propria

The posterior lingual gland opens onto the dorsal surface

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Posterior tongue behind circumvallate papillae

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Esophagus

Esophagus is a muscular tube extends from the pharynx to the stomach

Histologically it consists of four layers: mucosa submucosa muscularis externa adventitia / serosa

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Upper esophagus

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Mucosa Mucosa consists of three parts:

epithelium – nonkeratinized stratified squamous epithelium

lamina propria – lies below the epithelium, consists of thin layer of fine connective tissue, contains small blood vessels, diffuse lymphatic tissue and a small lymphatic nodule

muscularis mucosae – consists of a layer of longitudinal smooth muscle fibers

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Submucosa

Submucosa:

a wide layer of moderately dense irregular connective trissue,

Contains adipose tissue, esophageal glands and blood vessels

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Muscularis externa

Muscularis externa located inferior to the submucosa

Composed of two well-defined muscle layers: inner circular and outer longitudinal

Muscularis externa in: Upper third of esophagus consists of skeletal muscles

Middle third consists of both skeletal and smooth muscle

Lower third, only smooth muscle is present

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Adventitia / serosa

Adventitia / Serosa : In the thoracic cavity, the outer most layer of the

esophagus is called adventitia

In the abdominal cavity, the outer most layer of the esophagus is called serosa

It consists of connective tissue layer and contains adipose tissue, blood vessels and nerves

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Esophageal-stomach junction

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StomachStomach is a dilated segment of the digestive tract, that

digest food and secrets hormoneThere are three histological regions:CardiaFundus and bodyPylorusThe fundus and body are identical in microscopic

structureThe mucosa and submucosa of the undistended stomach

lie in longitudinally directed folds known as rugaeWhen the stomach is filled with food, folds flatten out

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Histological structure

Stomach has four histologic layers:

MucosaSubmucosaMuscularis externaSerosa

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Stomach mucosa of the fundus and body

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Mucosa Mucosa consists of:Surface epithelium – simple columnar, that invaginates

to various extents into the lamina propria, forming gastric pits

Lamina propria – composed of loose connective tissue, contains gastric glands, lymphatic tissue or small lymph nodule

Gastric glands contain two distinct cell types – acidophilic parietal cells and basophilic chief cells

Muscularis mucosae

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Submucosa

Submucosa lies below the muscularis mucosae

It is composed of dense irregular connective tissue

It contains small blood vessels, and isolated or clusters of parasympathetic ganglia of the submucosal (Meissner’s) nerve plexus

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Muscularis externaMuscularis externa consists of three layers of smooth

muscle

Inner oblique muscle layer

Middle circular muscle layer

Outer longitudinal muscle layer

Myenteric (Auerbach’s) nerve plexus of parasympathetic ganglia and nerve fibers is located between the circular and longitudinal smooth muscle layers

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Serosa

Serosa consists of thin connective tissue that overlies the muscularis externa

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Fundic mucosa

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Basal region of fundic mucosa

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Mucosa of pyloric region

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Difference between cardia, fundus & body, and pylorus

Cardia Fundus & body Pylorus

Contain cardiac gland Contain gastric gland Contain pyloric gland

Gastric pit less deeper than pyloric gland

Gastric pit less deeper than pyloric gland

Gastric pit more deeper than gastric or cardiac gland

Parietal cells absent or very few

Parietal cells more Parietal cells few

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ReferencesBasic Histology – Luis Carlos Junqueira, 11th edition

diFiore’s Atlas of Histology – 10th edition

Histology A Text and Atlas – Michael H. Ross, 4th edition

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