Histology of gut tube wall

Question 1

Four distinct layers of the gut tube wall

Answer 1

Mucosa (innermost)
Submucosa
Muscularis externa
Serosa/Adventitia

Question 2

Three sub-layers of the mucosa

Answer 2

Epithelium (innermost)
Lamina propria
Muscularis mucosae

Question 3

Describe the histology of the epithelium

Answer 3

In the mouth, oesophagus and anal canal: stratified squamous epithelium (less keratin than normal skin)

In the stomach and intestines: simple columnar epithelium - single layer of cells minimises distance for diffusion

Question 4

Describe the histology of the lamina propria

Answer 4

Loose connective tissue

Contains glands and blood/lymph vessels

Question 5

What is the main role of lymph vessels in the lamina propria?

Answer 5

To drain the products of fat digestion

Question 6

Describe the histology and function of the muscularis mucosae

Answer 6

Thin layer of smooth muscle

Function is mainly structural (very little other use)

Question 7

Give the function(s) of the epithelium

Answer 7

Barrier separating lumen of alimentary canal from the rest of the body
Synthesis and secretion of digestive enzymes, hormones and mucus
Selectively absorbs products of digestion

Question 8

Describe the structure and function of the submucosa

Answer 8

Thick, irregular connective tissue
Main function is to support the mucose
Also contains neurones (submucosal plexus), blood vessels and lymphatic vessels
Oesophageal and duodenal submucosa contain glands that secrete mucus and bicarbonate respectively

Question 9

Which two plexuses make up the enteric nervous system?

Answer 9

Submucosal (Meissner’s) plexus and Myenteric (Auerbach’s) plexus

Question 10

What does the duodenal submucosa secrete and why?

Answer 10

Bicarbonate to neutralise the stomach acid

Question 11

Describe the structure and function of the muscularis externa

Answer 11

Two concentric thick layers of smooth muscle

• Inner layer is circular muscle which contracts to constrict the lumen
• Outer layer is longitudinal muscle that contracts to shorten the gut tube

Produces motility (peristalsis and segmentation)

Question 12

Where is the myenteric (Auerbach’s) plexus?

Answer 12

Between the circular and longitudinal muscle layers of the muscularis externa

Question 13

Describe the location, structure and function of the serosa

Answer 13

Inside the peritoneal cavity
Connective tissue (outer layer of alimentary canal)
Surrounds stomach, small intestine and large intestines

Question 14

Describe the location, structure and function of the adventitia

Answer 14

Outside the peritoneal cavity
Connective tissue (outer layer of alimentary canal)
Attaches oesophagus and rectum to surrounding structures