Histology of the GI Tract

Question 1

What are the 4 layers of the GI tract ?

Answer 1

mucosa, submucosa, muscularis externa, adventitia/serosa

Question 2

Define Mucosa

Answer 2

• innermost layer, contains the epithelial cells important in lubrication & absorption

Question 3

Define Submucosa

Answer 3

• this layer contains the support network of blood vessels & immune cells to keep the mucosa healthy in addition to attaching it to the muscular layers below

Question 4

Define Muscular Externa

Answer 4

the muscles necessary for peristalsis are contained in this layer

Question 5

Define Adventitia/Serosa

Answer 5

• the outermost layer which allows the GIT to interact with other tissues around it

Question 6

What are the 2 adaptions of the oesophagus ?

Answer 6

• mucosa is stratified squamous epithelium, the remainder of the GI tract is simple columnar
• outermost layer of oesophagus is an adventitiam, remainder of tract is serosa

Question 6

What is the benefit of the stratified squamous epithelium of the oesophagus ?

Answer 6

• more adapted to resist mechanical abrasion

Question 7

Where does the oesphagus terminate ?

Answer 7

in the stomach

Question 8

Describe the mucosa of the stomach

Answer 8

• columnar epithelium, and forms ‘glands’ which house a range of important cell types

Question 9

Describe the muscular layer of the stomach

Answer 9

• contains 3 layers of muscles, this ensures efficient mixing, churning & emptying

Question 10

What are the functions of the stomach?

Answer 10

• digestion
• disinfection = the acidic environment in the stomach helps to kill any microbes
• mechanical breakdown = churning of the stomachs muscular contractions help to further macerate food

Question 11

What does the epithelium of the stomach form?

Answer 11

• forms pits which house gastric glands

Question 12

What cells are present in the stomach?

Answer 12

• Mucus cells
• Parietal cells
• Chief cells
• G cells

Question 13

What do mucus cells do?

Answer 13

• protects the stomach from the low pH environment

Question 14

What do parietal cells do?

Answer 14

• produce the sotmachs HCL, also makes intrinsic factor

Question 15

What is the function of Chief cells?

Answer 15

• produces pepsinogen, the zymogen of pepsin

Question 16

What is the function of G cells?

Answer 16

• secrete gastrin, which stimulates pepsinogen & HCL production

Question 17

What controls the passage of chyme from the stomach?

Answer 17

• the pyloric sphincter

Question 18

What are the 3 parts of the small intestine?

Answer 18

duodenum = major site of digestion
jejunum & ileum = 90% of absorption carried out in jejunum & ileum

Question 19

Where is bile produced?

Answer 19

in the liver

Question 20

Where is bile stored?

Answer 20

in the gall bladder

Question 21

How does bile enter the duodenum?

Answer 21

• squeezed into duodenum via the common bile duct where it can exert its role in fat digestion

Question 22

Describe the location of the pancreas

Answer 22

• lies posterior to stomach, running from the duodenum towards the spleen

Question 23

What are the endocrine & exocrine functions of the pancreas?

Answer 23

endocrine = acts on distant cells via circulation (secretion of insulin)
exocrine = acts via ducts or channels rather than blood (digestive enzymes into duodenum)

Question 24

What is the key cell of the endocrine part of the pancreas?

Answer 24

- beta-islet cells - which produce insulin

Question 25

What is the key cell of the exocrine part of the pancreas?

Answer 25

- Acinar cells - which produce digestive enzymes

Question 26

Describe Microvilli

Answer 26

- increase surface area of cell for nutrient absorption - approximately 0.1 um & 1 um tall - microvilli can also bud from their tips & this allows them to release useful substances they contain

Question 27

What are some cells present in the intestine?

Answer 27

- intestinal stem cells - paneth cells - goblet cells - enterocytes - transit amplifying cells - enteroendocrine cells

Question 28

Whats the function of intestinal stem cells?

Answer 28

replace lost/damaged intestinal cells

Question 29

What's the function of paneth cells?

Answer 29

involved in intestinal defence

Question 30

What's the function of transit amplifying cells?

Answer 30

intermediates bewteen stem cells & enterocytes

Question 31

What's the function of goblet cells?

Answer 31

produce lubricating mucus

Question 32

What's the function of enteroendocrine cells?

Answer 32

secretes hormones

Question 33

What's the function of enterocytes?

Answer 33

absorbs nutrients

Question 34

What is a Lacteal ?

Answer 34

- villi contain them - they're capillaries of the lymphatic system - lipids are transported away from the GI tract by lacteals

Question 35

Describe the Large Intestine

Answer 35

- horseshoe shaped - begins at exit of ileum & terminates at the anus - runs around outside of small intestine - 1.5 metres long & 7.5 cm wide

Question 36

What are the functions of the large intestine ?

Answer 36

- reabsorption of water & electrolytes from intestinal juices - compaction of intestinal contents into faeces - storage of fecal material - absorption of important vitamins produced by bacteria (biotin. B12, folic acid)