Histology of Digestive tract

Dr Abubakr H MossaMBBS, 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)

1. Mucosa2. Submucosa 3. Muscle layer

(muscularis externa)

4. Serosa or adventitia

General organization of GI tract (wall)

1. Mucosa:2. Submucosa 3. Muscle layer

(muscularis externa)

4. Serosa or adventitia

Formed by three layers;1. Epithelium: lining the inside of the

lumen. (functions?)2. Lamina propria (LP): loose

connective tissue. (Contents?)3. Muscularis mucosa: thin layer of

smooth muscle (inner circular & outer longitudinal) to change the shape of the mucosa.

General organization of GI tract (wall)

1. Mucosa2. Submucosa: 3. Muscle layer

(muscularis externa)

4. Serosa or adventitia

Moderately dense CT contains:1. Blood vessels2. Lymphatics, lymphoid follicles3. Nerves AND MEISSNER’S

PLEXUS (parasympathetic ganglia)

4. May contain glands…

General organization of GI tract (wall)

1. Mucosa2. Submucosa 3. Muscle layer:

(muscularis externa)

4. 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)

1. Mucosa2. Submucosa 3. Muscle layer

(muscularis externa)

4. 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 & skeletalLower 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 Present

• 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

• The simple columnar epithelium (in the epithelium & glands) is composed of six cell types:

1. Surface-lining cells: thick mucus2. Mucous neck cells: lubricating mucus3. Regenerative (stem) cells4. Parietal (oxyntic) cells: HCl & gastric intrinsic

factor5. Chief (zymogenic) cells; pepsinogen & gastric

lipase6. Diffuse neuroendocrine system (DNES) cells (also

known as amine precursor uptake and decarboxylation [APUD] and enteroendocrine cells).

All in the fundic glands!

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 Present

Muscle layer Present

Serosa / adventitia Present

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 Present

Serosa / adventitia Present

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 Present

Serosa Present

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 Present

Muscle layer Present 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