The oesophagus and stomach

Question 1

What are the layers of the gut wall?

Answer 1

Mucosa

Submucosa

Muscularis

Serosa

Question 2

What does the mucosa contain?

Answer 2

Epithelia

Lamina propria

Muscularis mucosae

Question 3

What does the submucosa contain?

Answer 3

Connective tissue with nerve plexi - drives movement of food bolus

Question 4

What does the muscularis contain?

Answer 4

Smooth muscle, with nerve plexi - for movement

Question 5

What does the serosa contain?

Answer 5

Connective tissue - holds gut to body wall

Question 6

What is the function of the oesophagus?

Answer 6

Thoracic structure that allows food to travel from mouth (pharynx) to stomach

Question 7

Where does the oesophagus originate and terminate? Which structures does it pass by? Why is this a problem?

Answer 7

C5, ends at T10
Passes close to the trachea, aorta and diaphragm
Any oesophageal problem can affect these structures

Question 8

How are the epithelia specialised for its function?

Answer 8

Non-keratinising

Wear and tear lining

Lubrication - mucous secreting glands

Question 9

How is oesophageal muscle specialised for its function?

Answer 9

Sphincters at both ends that are tonically active which close when no food.

Upper = skeletal
Lower = skeletal and smooth

Swallowing centre in brain that allows for voluntary control of the upper oesophageal sphincter

Question 10

How is oesophageal muscle specialised for food bolus movement?

Answer 10

Circular and longitudinal muscles in oesophagus for food bolus movement
- nervous stimulus causes muscle contraction and relaxation above and below bolus respectively

If food is stuck, second peristaltic wave initiated by nervous stimulus to brain

Question 11

Describe the structure of the gastro-oesophageal junction

Answer 11

Where oesophagus meets stomach.

Epithelial transition - oes to stom
- stratified squamous to columnar

Presence of folds
- Gastric rugae

Question 12

Describe the function of the gastro-oesophageal junction, the rugae and summarise its states.

Answer 12

Reduce acid-reflux
Epithelial transition allows for lesser effects of acid.

Contains rugae which allow stomach to reduce in size when empty and vice versa

On lack of food, diaphragm and empty stomach cause junction opening to be very narrow.
Food bolus acts as stimulus to relax diaphragm and open stomach

Question 13

How is acid-reflux meant to be prevented?

Answer 13

Diaphragm contracts

But can fail as fetus pushes stomach upwards, leading to pressure differences and causing acid to move upwards.

Question 14

What are the main functions of the stomach?

Answer 14

Break food into smaller particles

Hold food and release ar controlled rate

Kill parasites and certain bacteria

Question 15

Describe the structure of the stomach, distinguishing between the functional regions and their functions

Answer 15

Has simple columnar cells, which invaginate into mucosa.

The regions are:
Cardia and pylori
- Start and end of stomach
- Highly mucosal

Body and fundus

• Site of digestion and acid production by PARIETAL cells
• Highly acidic and lots of pepsinogen produced by CHIEF cells

Antrum
- Gastrin - endocrine function that stimulates acid production

Question 16

Describe the acid produced by the stomach and methods to protect against it.

Answer 16

2L a day,

Stomach lining has mucosal cells that release mucus with HCO3-, this protects the cells from the acid

Question 17

How is food moved in the stomach?

Answer 17

Peristalsis

• ANS - central
• 20pc of contractions

Segmentation

• ENTERIC NS - local
• Weaker
• Allows fluid to move to pyloric sphincter
• Anything solid is pushed back up

Question 18

Structure of Chief cell

Answer 18

• Lot of RER
• Lot of Golgi
• Lot of apical secretion granules

Question 19

Function of Chief cell

Answer 19

Pepsinogen secreting cell

Question 20

Structure of parietal cell at rest and when active

Answer 20

Resting

• Lot of mitochondria
• Canaliculi - large reservoirs close to surface
• Cytoplasmic tubulovesicles with H+/K+ ATPase

Active
- Tubulovesicles fuse with membrane, project into canaliculi

Question 21

Function of parietal cell

Answer 21

Acid secreting cell

When active, tubulovesicles fuse with canaliculi and allow for a large reservoir to form which can allow acid expulsion

Question 22

How is acid in the parietal cell produced?

Answer 22

Carbonic anhydrase abundance

• Produces H+ and HCO3- from H2O and CO2 -
• HCO3- is exchanged for Cl-
• Na+/K+ pump which allows K+ into the cell.
• K+ diffuses into lumen, pumped back in which moves H+ out

Question 23

What occurs following acid production?

Answer 23

Chief cells produce pepsinogen, which is activated to pepsin by the acid.

This can then digest proteins.

Question 24

Where is gastrin made and what is it used for?

Answer 24

Endocrine hormone made in the pyloric antrum

Excreted into blood and then returns to stimulate acid production by histamine release from chromaffin cells.
- Released when food in stomach.

Question 25

What are the phases of gastric secretion? Which are stimulatory or inhibitory?

Answer 25

Cephalic STIM
- secretion based on thought, sight etc of food - PREP for bolus - brain responds to sensory stimuli, activating vagus nerve, starting acid and pepsin production - ACh

Gastric STIM

• food in stomach, more powerful response
• lining of gut has nerves which respond to local stimuli
• stretch and chemo receptor in stomach - activate muscles and glands to aid digestion

Intestinal INHIB

• food left stomach - chyme
• response to chyme and stuff, relayed to brain
• inhibitory effect on stomach - enterogastric effect - hormones produces by cells of small intestine that switch off acid and pepsinogen production.

Intestinal EXCIT

• depends on protein levels
• if high, digestion not completed
• hence, gastrin is secreted

Question 26

Drug development for acid secretion redcution

Answer 26

Drugs that target acid secretion

Interfere with

• ACh
• Histamine - RANITIDINE
• Gastrin
• H+/K+ exchange - OMEPRAZOLE