0211 - GIT Mucosal Histology

Question 1

What are the four histological layers of the GIT?

Answer 1

Mucosa
Submucosa
Muscularis propria
Adventitia (+ Serosa)

Question 2

Describe the mucosal layer of the GIT.

Answer 2

Consists of epithelium (squamous or columnar), the lamina propria, and muscularis mucosae.

Question 3

Describe the submucosal layer of the GIT.

Answer 3

Loose collagenous tissue containing blood vessels, lymphatics, nerve submucosal plexuses, and lymphoid aggregates.

Question 4

Describe the muscularis propria of the GIT.

Answer 4

Two layers of smooth muscle (inner circular and outer longitudinal), allows for peristalsis, and myenteric nerve plexuses.

Question 5

Describe the Adventitia of the GIT.

Answer 5

Loose supporting (connective) tissue containing blood vessels and nerves. For the most part (except upper oesophageous and retroperitoneal areas - some duodenum, ascending, descending colon and rectum) is covered in mesothelial serosa as the outermost layer. In some parts of the bowel, adventitia is minimal to non-existent.

Question 6

What are the functions of GIT mucosa?

Answer 6

Protection - barrier to external environment.
Secretion - and synthesis of various substances (enzymes, mucus, hormones)
Absorption - products of digestion, water, electrolytes.
Immunological functions - containing lymphoid tissue.

Question 7

Describe the oesophageal mucosa.

Answer 7

Stratified squamous epithelium, with thin lamina propria containing lymphoid tissue.

Question 8

Describe the oesophageal submucosa.

Answer 8

Contains elastic fibres (allow distension) and mucous glands (lubricate bolus).

Question 9

What happens at the gastro-oesophageal junction? How can this change with Barrett’s Oesophagus?

Answer 9

Stratified squamous of the oesophagus changes to architecturally glandular columnar epithelium of stomach. In Barrett’s, following repeated reflux, stratified squamous undergoes metaplasia into columnar epithelium resembling small bowel.

Question 10

What is the architecture of the stomach mucosa?

Answer 10

Fundus and body consist of straight tubular glands (simple columnar), with large mucigen granules (NOT goblet cells) to protect the epithelium. Surface mucous cells secrete HCO3- as well.

Question 11

What are the cell types of the gastric glands?

Answer 11

Parietal cells secrete gastric acid and intrinsic factor. Stain pink (mitochondria).
Chief cells secrete pepsin, stain blue (ribosomes)
Neuroendocrine cells secrete hormones (serotonin, gastrin)
Stem cells can differentiate into the others as required.

Question 12

Describe the histological layers of the stomach.

Answer 12

Columnar epithelium with tubular glands.
Very thin lamina propria
Submucosa contains nerves and ganglia making up submucosal plexus.
Muscularis propria contains a third, ‘inner oblique’ layer.
Serosa.

Question 13

What happens histologically at the gastro-duodenal junction?

Answer 13

Simple columnar epithelium changes to villous mucosa lined by columnar mucosa with goblet cells in duodenum.

Question 14

Describe the small intestine mucosa at low power.

Answer 14

Consists of villi (finger-like projections), which are longest in the duodenum and shorter in the ileum.
Crypts of Lieberkuhn lie between the villi.
Peyers patches are lymphatic tissue within the lamina propria.

Question 15

Describe the cells of the small intestine epithelium.

Answer 15

Simple columnar epithelium consisting of:
Enterocytes - absorptive cells with microvilli, covering the villi and crypts
Goblet cells - scattered along epithelium, produce mucus.
Paneth cells - at base of crypts, contain secretory granules of lysozymes, can phagocytose some bacteria/protozoa.
Neuroendocrine cells - produce hormones such as secretin
Stem cells - at base of crypts
Intraepithelial lymphocytes - mainly T cells.

Question 16

What happens at the Ileo-caecal junction?

Answer 16

Villous columnar mucosa with goblet cells and Paneth cells changes to mucosa with crypts lined by columnar mucosa with goblet cells of large intestine.

Question 17

Describe the large intestine mucosa.

Answer 17

Simple columnar epithelium which forms tubular glands (crypts)
Enterocyte - absorptive cell with microvilli (most common cell type)
Goblet Cells - for mucus.
Stem cells at base of crypts.

Question 18

What is unique about the histology of the appendix?

Answer 18

Abundant lymphoid tissue (like ileum), but contains large intestine mucosa - no villi or microvilli.

Question 19

What happens at the rectoanal junction?

Answer 19

Glandular mucosa of the rectum changes to stratified squamous of the anus.

Question 20

Why is it important to know the histology of each part of the GIT?

Answer 20

Know what’s normal to identify abnormal. Very important in cancer staging (for management and prognosis)