Histology of the GI Tract Flashcards
The entire GI tract from oesophagus to anus present certain common histological features
What are the 4 distinct functional layers of the GI tract?
- Mucosa
-Epithelium
-Lamina Propria
Muscularis Mucosae - Submucosa
- Muscularis propria
- Serosa/ Adventitia
Describe the epithelial layer of the mucosa
Its type varies with functions.
Basement membrane supports epithelium and is not penetrated by blood vessels or nerve.
Describe the lamina propria of the mucosa layer
Layer of loose connective tissue rich in blood, lymph vessels and smooth muscle cells.
Glands are present throughout the tube except in the oesophagus
What are the 4 basic mucosal types found in the GI tract?
Protective
(stratified squamous)
- oral cavity, pharynx, oesophagus and anal canal
Secretory
(Simple columnar with tubular glands)
- Type seen only in the stomach
Absorptive
(Villi with short glands called crypts- Brunner’s glands (Duodenum))
- Typical of entire small intestine
Absorptive/Protective
(closely packed straight tubular glands with goblet cells)
-Lines the whole large intestine
The GI tract mucosa undergoes abrupt transition from one form to another at 4 junctions. What are these?
Gastro-oesophageal junction
Gastro-duodenal junction
Ileocaecal junction
Rectoanal Junction
Describe the histology of the oesophagus
Epithelium is non-cornified stratified squamous
Thick muscularis mucosa
Mucous alveoli of oesophageal glands in submucosa
Describe the histology of the stomach
Mucosa thrown into folds or rug with no villi and no goblet cells
Short gastric pits in upper part of mucosa
Abundant glands in deep zone of mucosa
Describe the distinctive histological features of the small intestine
The small intestine is divided into 3 regions: Duodenum, jejunum and ileum
Distinctive features of the small intestine:
-Villi (finger like projection of the mucosa)
- Columnar epithelium with striated borders
- Goblet cells (like bowl shaped drinking cups with no handles)
- Short tubular intestinal glands (crypts of leibemkuhn)
What are the cell types present on intestinal villi?
Enterocytes (absorptive cells)
Goblet cells (produce mucin- lubrication and protection)
Paneth cells and lymphocytes- defence
Neuroendocrine cells - secrete locally acting hormones (GI motility and secretion)
What are the histological features of the duodenum?
Short, leaf shaped villi, abundant and closely packed of varying hight
Extensive aggregation of mucous secreting runner’s glands in submucosa
No lymph nodes in submucosa
What are the histological features of the Jejunum?
Tongue shaped villi with swollen ends, less abundant and of different heights
Few goblet cells
Submucosa - few or no lymph nodules. peer’s patches are absent
Crypts only, no glands of brunner
What are the histological features of the jejunum?
Lymphoid aggregation of various size- Payer’s patches
Few finger shaped villi with variable upper level
Numerous goblet cells
Describe the histological features of the colon
Closely packed, long, straight tubular glands in vertical rows with abundant goblet cells
Prominent muscularis mucosae
Smooth mucosal surface (no villi)
Describe the histological features of the appendix.
Mucosa has no villi, fewer goblet cells as compared to colon.
Few, less well developed intestinal glands
Epithelium has tall columnar cells as in small intestine
Ring of lymph follicles in the lamina propria
Describe the histological features of the liver
Cells arranged in sheets, usually 1 cell thick, converting towards centre (like spokes of a cycle wheel)
Hexagonal lobules
Presence of portal tracts (blood vessels and tracts)
