Histology

Question 1

What are the 4 main layers of the GI tract, from the lumen outwards

Answer 1

Mucous membrane/mucosa - epithelium, connective tissue and thin, smooth muscle
Submucosa - Wide zone of connective and supporting tissue
Muscularis externa/propria - Two thick layers of smooth muscle; inner circular and outer longitudinal
Adventita/serosa - Thin outer covering of connective and supporting tissue

Question 2

Discuss the histology of the oesophagus

Answer 2

Comprised of non-keratinised stratified squamous epithelium. Contains numerous folds which gives the lumen a stellate shape and a prominent muscularis mucosae

Question 3

Identify the three layers of muscularis found in the stomach

Answer 3

Longitudinal
Circular
Oblique

Question 4

Discuss the histology of the parts of the stomach

Answer 4

Simple columnar epithelium present throughout.
Gastric pits open into gastric glands extending down the muscularis mucosae.
Cardia - Gastric pits contain short, coiled and branched glands
Body - Long, narrow gastric glands with mucous neck cells, parietal cells and chief cells
Pyloric Region - Contains deeper gastric pits

Question 5

Discuss the cell types found in the stomach

Answer 5

Mucous neck cells - Secretes mucous to lubricate the surface epithelium and protect the cells from the acidic and enzymatic properties of gastric juices
Parietal cells - Most abundant in upper parts of pits, they secrete HCl which provides an acidic environment for the enzymatic
breakdown of proteins in the chyme.
Chief cells - numerous found in the deeper parts of the gastric glands, these stain bluish. They produce pepsin which is a proteolytic enzyme activated by acid secretions

Question 6

Discuss histology of the duodenum

Answer 6

Presence of Brunner’s glands in the submucosa. They have an alkaline mucoid secretion which empties into the crypts of Lieberkuhn. This helps to neutralise the acidic chyme and protect the surface epithelial cells from acid-induced injury

Question 7

Discuss histology of the jejunum

Answer 7

Has the tallest villi, these extend from the circular folds of the mucosa and submucosa - the plicae circularis. No presence of Brunner’s glands

Question 8

Discuss the histology of the ileum

Answer 8

Identified by PEyer’s patches which are aggregated lymphoid follicles found in the submucosa which often breach the muscularis mucosae and extend into the lamina propria.

Question 9

Discuss the histology of the colon

Answer 9

Colon contains numerous crypts of Lieberkuhn, extending down to the muscularis mucosae. Also contains many goblet cells which are outnumbered by the absorptive enterocytes.
Presence of teniae coli also

Question 10

Discuss the histology of the rectum

Answer 10

Deeper mucosa here, colonic glands are often shorter. More goblet cells than the colon. Stratified squamous epithelium is seen at the junction of the rectum and anus. The muscularis externa also thickens here to form the internal anal sphincter