Histology of the GI tract

Question 1

What sort of epithelium lines the oral cavity, oropharynx and laryngopharynx?

Answer 1

Stratified squamous epithelium which is generally not keratinised

Question 2

Describe the epithelium on the anterior 2/3 of the tongue.

Answer 2

Stratified squamous epithelium which is thin on the ventral surface, and is thick and with papillae on the dorsal surface.

Question 3

Describe the epithelium on the posterior 1/3 of the tongue.

What is present in the submucosa?

Answer 3

It is covered with smooth stratified squamous epithelium.
It lacks papillae apart from the circumvalate papillae
There are substantial lymphoid aggregates in the submucosa.

Question 4

Name the four types of papillae on the tongue.

Which of these does not have any taste buds?

Answer 4

Circumvalate
Foliate
Fungiform
Filiform
The filiform papillae do not have any taste buds.

Question 5

What are the four major layers of the digestive tract architecture?

Answer 5

Mucosa: epithelium (which sits on a basal lamina), Lamina propria (loose connective tissue), and the muscularis mucosae (a thin layer of smooth muscle).
Submucosa: loose connective tissue
Muscularis externa: two thick layers of smooth muscle, an inner circular layer and an outer longitudinal layer
Serosa or adventitia: An outer layer of connective tissue that either suspends the digestive tract or connects it to other organs.

Question 6

Which layer of the digestive tract varies most between different parts of the digestive tract?

Answer 6

The mucosa

Question 7

Is there any skeletal muscle in the oesophagus?

Answer 7

Yes- superiorly, but it transitions to purely smooth muscle more distally.

Question 8

What type of epithelium lines the cardia of the stomach?

Answer 8

Columnar epithelium

Question 9

Describe the mucosa of the stomach.

Answer 9

Columnar epithelium. There are gastric pits with gastric glands beneath them which secrete the acid and enzymes required to begin digestion.

Question 10

What sort of cells lines gastric pits?

Answer 10

Surface mucous cells

Question 11

What is the name of the invagination in a parietal cell that gives it an increased surface area?

Answer 11

Canaliculus

Question 12

Which cells secrete pepsinogen?

How is it stored in these cells?

Answer 12

Chief cells.

It is stored as zymogen granules of pepsinogen.

Question 13

What are there lots of in parietal cells?

Answer 13

tubulovesicles containing proton pumps, and mitochondria.

Question 14

Describe how the mucosa varies in the different regions of the stomach.

Answer 14

Cardia: Deep gastric pits that branch into loosely packed, tortuous glands
Body: Shallow gastric pits with long, straight gastric glands
Deep gastric pits with branched, coiled gastric glands at a higher density than in the cardia.

Question 15

How is the muscularis externa of the stomach unusual?

Answer 15

In some areas it contains an extra layer of smooth muscle which runs oblique to the circular smooth muscle layer and longitudinal smooth muscle layer.
It runs internal to the circular layer.
This layer aids the churning action of the stomach.

Question 16

What becomes thickened to form the pyloric sphincter?

Answer 16

The inner, circular layer of smooth muscle.

Question 17

Describe the mucosa of the small intestine.

Answer 17

There are finger like projections called villi.

Between the bases of adjacent villi there are pits “drilling” downwards, called the Crypts of Lieberkuhn.

Question 18

Describe unique features of each of the parts of the small intestine.

Answer 18

Duodenum: Contain’s Brunner’s glands in the submucosa which produces a thin, alkaline mucous in response to the presence of chyme to neutralise it.
Jejunum: It has the tallest villi, located on permanent circular folds of the mucosa and submucosa called the plicae circularis.
Ileum: Has aggregations of lymphoid follicles called Peyer’s patches found in the submucosa and often extending into the lamina propria.

Question 19

Name the only 2 parts of the digestive tract which have submucosal glands.

Answer 19

The oesophagus and the duodenum.

Question 20

What do the submucosal glands in the oesophagus do?

Answer 20

They produce a lubricant to aid the passage of food through the oesophagus.

Question 21

What cells are found in the intestinal epithelium?

Name them and describe their function.

Answer 21

Enterocytes: they are the most numerous cells. They are tall columnar cells with a brush border and are the principle absorptive cell.
Goblet cells: produce mucin to protect the epithelium and lubricate the passage of material.
Paneth cells: found at the bases of crypts of Lieberkuhn and have a defensive function.
Neuroendocrine cells: Produce hormones that contribute to the control of secretion and motility.
Stem cells: Found at the bases of the crypts of Lieberkuhn, and divide to replenish the epithelium.

Question 22

Describe the enterocytes of the small intestine.

Answer 22

Simple columnar epithelium with a brush border.

Question 23

Describe the plicae circularis.

Answer 23

In the jejunum

They are folds of the mucosa and submucosa with villi.

Question 24

Describe the lymphoid tissue in the small intestine.

Answer 24

There is a substantial amount of lymphoid tissue in the gut, called “gut associated lymphoid tissue” (GALT). Much of this consists of scattered lymphocytes, but areas of relatively large aggregations of lymphoid tissue exist, particularly in the ileum, called “Peyer’s patches”.
They can extend up into the lamina propria and sometimes even into the epithelium.

Question 25

What are the two principle cell types in the epithelium of the large intestine?

Answer 25

Absorptive cells and Goblet cells.
Absorptive cells: For removal of salts and thereby water
Goblet cells: For the secretion of mucous to lubricate the colon.

Question 26

Describe the mucosa of the large intestine.

Answer 26

The epithelium is arranged in straight, tubular glands, referred to as crypts, which extend all the way down to the muscularis mucosa.
The lamina propria pokes up between each crypt.

Question 27

What is different about the longitudinal muscle in the large intestine compared to other parts of the digestive tract?

Answer 27

It is not continuous, but is found in 3 muscular strips called teniae coli.

Question 28

What type of epithelium lines the anal canal?

Answer 28

Stratified squamous epithelium which is connective with the stratified squamous epithelium of the surrounding skin as you move out of the anal canal.
It begins as non-keratinised but becomes keratinised.

Question 29

What is the nervous system in the gut called?

Where does it receive input from?

Answer 29

The enteric nervous system

It receives input from the autonomic nervous system but is capable of coordinating gut motility locally.

Question 30

Where is the myenteric plexus of the enteric nervous system found?
What does it control?

Answer 30

It is found between the layers of circular and longitudinal smooth muscle.
It controls gut motility.

Question 31

What is the plexus found in the submucosa called?

What does it control?

Answer 31

It is called the submucosal plexus.

It controls the muscle of the muscularis mucosae and also helps regulate secretion in the epithelium.

Question 32

Summarise the type of epithelium which lines a)oral cavity, pharynx, oesophagus and anal canal

b) the stomach
c) the small intestine
d) the large intestine

Answer 32

a) Non-keratinised stratified squamous epithelium which has a protective function
b) Simple columnar epithelium with extensive tubular glands which has a secretory function
c) Simple columnar epithelium with tubular glands, which has an absorptive function
d) Simple columnar epithelium with tubular glands which has a protective and absorptive function.