Lecture 4: Epithelia of the gut and layers of GI tract

Question 1

What are the 2 main types of epithelium in the gut?

Answer 1

-stratified squamous non-keratinised (oesophagus and distal anus)
Non-keratinised because cells are usually keratinised to prevent water loss from the skin, but they secrete mucus to provide protection and lubrication
-simple columnar (stomach to proximal anus)
The columnar cells are specialised at different regions of the gut.

Question 2

Why is stratified squamous epithelium found at oesophagus and distal anus?

Answer 2

Resists physical and chemical abrasion ( hard food being eating/excreted)

Question 3

What is the function of columnar epithelium in the stomach?

Answer 3

Secrete mucin (surface mucus cells)
These dip down to form gastric pits, at the base of these pits are gastric glands.
At the base of these pits you transition from surface mucus cells to neck mucus cells

Question 4

Where do the gastric glands lie in the stomach?

Answer 4

Lamina propria

Question 5

How do the neck mucus cells differ from the surface mucus cells?

Answer 5

They are smaller, more irregulary shaped as they are compressed by surrounding cells, contain smaller vacuoles of mucin

Question 6

What is the role of mucus producing cells?

Answer 6

Protect the stomach epithelia against the acidic environment

Question 7

What are the surface modifications of the small intestine to increase SA?

Answer 7

• plicae circulares (endulating area/folds)
• villi are found on these folds and on the apical surface of the villi is microvilli
• inbetween the villi are crypts (invaginations): in large intestine also

Question 8

What cells have microvilli on their apical surface?

Answer 8

Enterocytes

Question 9

What cells are found near the enterocytes?

Answer 9

Goblet cells which contain mucin

Question 10

What cells are found in the crypts?

Answer 10

• Contain stem cells, which constantly divide and replace epithelia every 2-4 days
• paneth cells which secrete antibacterial proteins to protect the stem cells
• enteroendocrine cells: hormone producing cells to control the functions of the gut

Question 11

What glands are found in the proximal duodenum?

Answer 11

Brunner’s glands

-produce alkaline mucoid material which neutralises the acidic chyme coming from the stomach

Question 12

Where do products go once passed through the enterocytes?

Answer 12

Into the blood supply/lymph.

Most lipids enter the lymphatic capillary

Question 13

What is the structure of the large instestine/colon?

Answer 13

Tall columnar epithelia: Colonocytes which are folded
-these form crypts between them, which contain stem cells and enteroendocrine cells
Have large goblet cells to produce mucus which is required to sustain the microbiome and forms a barrier b/w the microbiome and the epithelia

Question 14

Does the large intestine have villi?

Answer 14

No

Question 15

Why do the columnar cells in the colon have prominent lateral intercellular spaces?

Answer 15

To allow for active fluid absorption

Question 16

What ionic pump is found in the columnar cells of the colon?

Answer 16

Na+/K+ pump, meaning there is a low intracellular Na+ in the colonocyte and in lateral intercellular spaces, allowing Na+ to move into the colonocyte, bringing in water with it due to osmosis

Question 17

What type of surface is the gut?

Answer 17

Exterior surface as is in contact with the outside world

Question 18

What are the different layers of the gut? (inner to outer)

Answer 18

• mucosa
• submucosa
• muscularis propria (inner & outer)
• serosa

Question 19

What is the mucosa layer composed of?

Answer 19

3 layers

• epithelial layer which is directly in contact with the contents of the gut
• -lamina propria
• muscularis mucosa

Question 20

What is the function of the epithelia?

Answer 20

Selectively permeable barrier, facilitating the transport of digested food.
-produces hormones and mucus

Question 21

What is the function of the lamina propria?

Answer 21

Contains macrophages and lymphoid nodules and produces antibodies, helping to protect us against bacterial and viral invasion through the gut

Question 22

What antibodies does the lamina propria of the gut produce?

Answer 22

IgA as they are resistant to proteases

Question 23

What is the function of the muscularis mucosa?

Answer 23

Layers of smooth muscle running in different directions to help keep epithelium in contact with gut contents to improve absorption and keep the crypts dynamic

Question 24

What is present in the submucosa?

Answer 24

• glands
• blood vessels
• lymphoid tissue
• submucosal plexus (part of the enteric nervous system)

Question 25

What does the muscularis propria contain?

Answer 25

Inner circular muscle and outer longitudinal muscle
-when circular muscle constricts it reduces diametre
-when longitudinal muscle constricts it changes the length of the gut
THIS ENABLES US TO DO PERISTALSIS
-inbetween the two muscular layers there is the myenteric plexus (part of enteric nervous system)

Question 26

What does the serosa contain?

Answer 26

• blood vessels
• lymphatic vessels
• adipose tissue