Histology of gastrointestinal tractHistology of gastrointestinal tractHistology of gastrointestinal tractHistology of gastrointestinal tract

Gastrointestinal tract has four distinct layers Mucosa Mucosa

Epithelium

L i i i f i Lamina propria – supporting function Consist of loose connective tissue (elastic fibers), vessels, nerves,

l d l h id i (i i )glands, lymphoid aggregation (immunity)

Muscularis mucosae – thin smooth muscle layer that is involved in the movement of mucosa

Submucosa Consist of loose connective tissue, large vessels, nerves,Consist of loose connective tissue, large vessels, nerves,

glands, submucosal, submucosus nerve plexus (Meissner´s plexus), and lymphoid aggregation (immunity)gg g

Muscularis propria Muscular wall consist of smooth muscle arranged in two Muscular wall consist of smooth muscle arranged in two

layers, inner circular and outer longitudinal Participate in the peristaltic contraction Participate in the peristaltic contraction Myenteric nerve plexus (Auerbach´s plexus) is located

between these two layersbetween these two layersAdventitia (serosa)

C i f l i i l l Consist of loose connective tissue, large vessels, nerves, adipose tissue covered by the simple squamous epithelium (mesothelium)(mesothelium)

Microscopic preparation Microscopic preparation –– the mucosa of the the mucosa of the tonguetongue

Circumvallate papillae

Stratified squamous epithelium

Taste buds embedded in the epithelium Taste buds embedded in the epithelium

Lamina propria form the body of papilla

Microscopic preparation Microscopic preparation –– the mucosa of the the mucosa of the tonguetonguetonguetongue

Circumvallate papilla Filiform papilla

epithelium

Lamina propria mucosae

Taste buds

Microscopic preparation Microscopic preparation –– the mucosa of the the mucosa of the tonguetongue (taste buds)(taste buds)

Taste bud

Microscopic preparationMicroscopic preparation –– EsophagusEsophagus

Mucosa Stratified squamous epithelium Stratified squamous epithelium

mechanical protection Lamina propria mucosae

l i i l h id i (i i ) loose connective tissue, lymphoid tissue (immunity) Muscularis mucosae

Submucosa

Muscularis propria Inner circular smooth muscle layer Outer longitudinal smooth muscle layer

Ad i i Adventitia

Muscularis propria

EsophagusEsophagusp p

submucosa

mucosa

Microscopic preparationMicroscopic preparation –– EsophagusEsophagus

Epithelium

L h dLymph node

Lamina propria mucosae

Lamina muscularis mucosaemucosae

Submucosa

Microscopic preparationMicroscopic preparation –– EsophagusEsophagus

Circular Longitudinal

Microscopic preparationMicroscopic preparation –– StomachStomach MucosaMucosaMicroscopic preparation Microscopic preparation –– StomachStomach -- MucosaMucosa

Mucosa Simple columnar epithelium enters lamina propria and form the

gastric pits Gastric glands enters these gastric pits

Cell population of epitheliump p p Surface mucous cells – production of protective bicarbonate ions

(against hydrochloric acid)( g y ) Parietal (oxyntic) cells – production hydrochloric acid Zymogenic (peptic) cells – located towards the base of the glandsy g (p p ) g

Pepsin – secreting cells

Neuroendocrine cells

Microscopic preparationMicroscopic preparation –– StomachStomachMicroscopic preparation Microscopic preparation –– StomachStomach

Muscularis mucosae – border between mucosa and submucosaS b i t f l ti ti d Submucosa – consist of loose connective tissue and large vessels

Muscularis propria – consist of three layers of smooth musclesmooth muscle Oblique layer

I i l Inner circular Outer longitudinal

Microscopic preparation Microscopic preparation –– StomachStomachp p pp p p

Mucosa

Gastric foldSubmucosa

Muscularis propria

Gastric pit

Mucosa

Gastric glands

Muscularis mucosaeMuscularis mucosae

Microscopic preparation Microscopic preparation –– SmallSmall intestineintestine --mucosamucosa

Mucosa and submucosa forms circular folds called li i lplicae circulares

Mucosa (epithelium and lamina propria) forms intestinal villiintestinal villi

Plica circularis (Kerckringi) -

submucosa

mucosa jejunum

Plica circularis

Circular

Muscularis propria

layer

p p

Longitudinal layer

Microscopic preparation Microscopic preparation –– Small intestine Small intestine --mucosamucosamucosa mucosa

Simple columnar epithelium covers surface of villi and forms intestinal glands

(Lieberkühn crypts)Cell population of epithelium (glands)

Enterocytes contain microvilli on the apical surface Enterocytes – contain microvilli on the apical surface Participate on the absorption

G bl ll l d Goblet cell – located among enterocytes Production of the protective mucin (against hydrochloric acid)

Paneth cells located at the base of the crypt protectivefunction ((againsagains bacteriabacteria))

Plica circularis (Kerckringi) -

submucosa

mucosa jejunum

Plica circularis

Circular

Muscularis propria

layer

p p

Longitudinal layer

SmallSmall intestineintestine –– mucosamucosa

Intestinal vilus

Intestinal glands(Lieberkühn)

Paneth cells

SmallSmall intestineintestine –– villivilli

Goblet cell

Connective tissue + vesselsConnective tissue + vessels

Enterocyte

PancreasPancreas

Pancreas is mixed exocrine (digestive system) and endocrine

gland.

Endocrine part forms pancreatic islets called islets of Endocrine part forms pancreatic islets called islets of

Langerhans

There are four types of cell including

Alpha cells secrete glucagon Alpha cells – secrete glucagon

Beta cells – secrete insulin

Delta cells – secrete somatostatin

F-cells - secrete pancreatic polypeptide

Blood capillaries surround all these cells

PancreasPancreas

Islets of Langerhans

Intrapankreatic vessel

duct

PancreasPancreas

Islets of Langerhans

Exocrine pancreas

g

Islets of LangerhansLangerhans

Islets of Langerhans

Microscopic preparation Microscopic preparation –– Liver Liver

B l i f li i h i l b lBase structural unit of liver is hepatic lobule It is hexagonaly in shape and is centered on the terminal hepatic

venule (centrilobular venule)venule (centrilobular venule)

Consist of hepatocytes, separated by the vascular channels called i id (bl d f h h i d l i )sinusoids (blood from the hepatic artery and portal vein)

The blood from sinusoids flows into the centrilobular venule → The blood from sinusoids flows into the centrilobular venule → hepatic vein → inferior vena cava

Bile is secreted by hepatocytes → enters bile canaliculi thatempty into small bile ducts

Portal tract (portal triad) located at the angles of the hexagon Portal tract is consist of the vein (branch of hepatic portal vein – nutrition),

the artery (br n h hep ti rter o gen) nd the bile ductthe artery (branch hepatic artery – oxygen) and the bile duct

HepaticHepatic lobulelobule

Portal triad

Vena centralis

PortalPortal triadtriad

bile duct

vein

artery

LiverLiver -- centrilobularcentrilobular venulevenule