Histology of Digestive tract Dr Abubakr H Mossa MBBS, 27/11/2012

Topic outlines.. General organization of GI tract (layers) Regional features (differences) in the histology of GI tract segments: Esophagus Stomach: Cardia Fundus (body) Pylorus Duodenum Jejunum Ileum Appendix Colon Anorectal junction

General organization of GI tract (wall) Mucosa Submucosa Muscle layer (muscularis externa) Serosa or adventitia

General organization of GI tract (wall) Mucosa: Submucosa Muscle layer (muscularis externa) Serosa or adventitia Formed by three layers; Epithelium: lining the inside of the lumen. (functions?) Lamina propria (LP): loose connective tissue. (Contents?) Muscularis mucosa: thin layer of smooth muscle (inner circular & outer longitudinal) to change the shape of the mucosa.

General organization of GI tract (wall) Mucosa Submucosa: Muscle layer (muscularis externa) Serosa or adventitia Moderately dense CT contains: Blood vessels Lymphatics, lymphoid follicles Nerves AND MEISSNER’S PLEXUS (parasympathetic ganglia) May contain glands…

General organization of GI tract (wall) Mucosa Submucosa Muscle layer: (muscularis externa) Serosa or adventitia Smooth muscle in two layers: inner circular & outer longitudinal (importance?) Between the two layers, MYENTERIC OR AUERBACH PLEXUS can be identified (motor parasympathetic function)

General organization of GI tract (wall) Mucosa Submucosa Muscle layer (muscularis externa) Serosa or adventitia In the intraperitoneal organs: serosa (formed by thin CT layer covered by mesothelium) In extraperitoneal organs: adventitia (thin layer of CT only)

Regional histology of GI tract

Esophagus Layer Features Mucosa Epithelium Stratified squamous non-keratinized LP Thin CT Muscularis mucosa Thick Longitudinal layer only Submucosa Thrown into fold Esophageal glands Muscle layer Upper 1/3: skeletal Middle 1/3: smooth & skeletal Lower 1/3: smooth Serosa / adventitia All adventitia except the lower 1 inch

Esophagus: GL: glands in the submucosa

Cardio-esophageal junction: notice the change in the epithelium from ………… to ………….

Stomach: general features Layer Features Mucosa Epithelium Simple columnar, contains depressions called gastric pits (lead to the gastric glands) LP Contains GASTRIC GLANDS Muscularis mucosa Two layers Submucosa Present Muscle layer Three layers: inner oblique, middle circular & outer longitudinal Serosa The mucosa and submucosa of the stomach show longitudinal folds called RUGAE which disappear on distention

Stomach: regions Three different histological regions: Cardiac Fundic (body) Pyloric They differ mainly in the arrangement of the gastric glands:; Cardiac: shallow gastric pits, cardiac glands are coiled & mucus secreting Fundic: deep gastric pits (1/2 of the LP), fundic glands contain all types of cells (discussed later) Pylorus: deepest gastric pits (>1/2 of LP), pyloric glands contain all types (but mucus neck cells are more)

Stomach: cells All in the fundic glands! The simple columnar epithelium (in the epithelium & glands) is composed of six cell types: Surface-lining cells: thick mucus Mucous neck cells: lubricating mucus Regenerative (stem) cells Parietal (oxyntic) cells: HCl & gastric intrinsic factor Chief (zymogenic) cells; pepsinogen & gastric lipase Diffuse neuroendocrine system (DNES) cells (also known as amine precursor uptake and decarboxylation [APUD] and enteroendocrine cells). In the upper ½ of the gland In the lower 1/3 of the gland

Small intestine; general features Three parts: Duodenum: 12 cm Jejunum: 2 m Ileum: 3 m Mucosa & submucosa thrown into circular folds called PLICAE CIRCULARIS (permanent?) VILLI: finger like mucosal projections (0.5 mm) Between the villi: the invaginations into the LP form INTESTINAL GLANDS (CRYPTS OF LEIBERKUHN) Microvilli? Goblet cells? Cells: refer to the diagram

Duodenum Layer Features Mucosa Epithelium Simple columnar LP Few intestinal glands Muscularis mucosa present Submucosa BRUNNER’S GLANDS: or duodenal glands Muscle layer Present Serosa / adventitia Serosa Present (except?)

Notice the duodenal glands in the submucosa

Jejunum Layer Features Mucosa Epithelium Simple columnar LP Intestinal glands Muscularis mucosa Present Submucosa Muscle layer Serosa / adventitia

Jejunum

Ileum Layer Features Mucosa Epithelium Simple columnar LP Intestinal glands & PEYER’S PATCHES (large lymphoid follicles) Muscularis mucosa Present Submucosa Present (Peyer’s patches may extend into this layer) Muscle layer Serosa / adventitia

Ileum showing Peyer’s batches

Large intestine: general features Consists of: Cecum Appendix Colon (ascending, transverse & descending) Sigmoid Anal canal Epithelium is simple columnar with plenty of goblet cells LP occupied by long tubular glands No plica circularis nor villi Microvilli present

Appendix Layer Features Mucosa Epithelium Simple columnar with plenty of goblet cells and immune cells LP Intestinal glands & large lymphoid follicels Muscularis mucosa Present Submucosa Present (some lymphoid follicles may extend to this layer Muscle layer Serosa The whole lumen can be seen under low power

Colon Layer Features Mucosa Epithelium Simple columnar with plenty of GOBLET CELLS LP Tubular glands Muscularis mucosa Present Submucosa Muscle layer But the outer longitudinal is modified into three bands called TINEA COLI Serosa / adventitia Present (except?)

Rectum Similar to the colon except that the folds are longitudinal and the tinea coli are absent

Thanks