Upper GI tract

Question 1

What is digestion?

Answer 1

Process of breaking down macromolecules to allow absorption

Question 2

What is absorption?

Answer 2

Process of moving nutrients and water across a membrane

Question 3

What makes up the upper GI tract?

Answer 3

Oesophagus, stomach, foregut (liver, pancreas, gall bladder and part of duodenum)

Question 4

What are the different layers of the gut wall?

Answer 4

Mucosa:

• epithelium
• lamina propria
• muscular mucosae

Submucosa:
- connective tissue (containing nerve plexus)

Muscularis:
- smooth muscle (containing nerve plexus)

Serosa/ adventitia:
- connective tissue +/- epithelium

Question 5

How many teeth are in the oral cavity?

Answer 5

8 incisors
4 canines
8 premolars
12 molars

32 teeth in total

Question 6

What is the role of salivary glands in the oral cavity?

Answer 6

Food mixes with saliva (aqueous secretion and digestive enzymes)
Lingual lipase secreted for fat digestion
Salivary amylase secreted for carbohydrate digestion

Question 7

How is the tongue moved?

Answer 7

Intrinsic muscles: fine motor control and moving food

Extrinsic muscles: gross movement of tongue (in, out, up and down). Assists mechanical digestion

Question 8

What is the function of the oesophagus?

Answer 8

Conduit for food, drink and swallowed secretions from pharynx to stomach

Question 9

How is the oesophagus epithelium structured?

Answer 9

Has a non-keretanising squamous epithelium
Has wear and tear lining which protects from extreme temps, texture and acid reflux
Has lubrication- mucus secreting glands and saliva

Question 10

What structure can be found at the top and bottom of the oesophagus?

Answer 10

Upper oesophageal sphincter: a true sphincter

Lower oesophageal sphincter: not sure if true or not

Question 11

What is Barretts oesophagus?

Answer 11

Epithelium of lower oesophagus undergoes metaplasia to go from squamous to columnar
Gastric mucosa extends into oesophagus (red in colour)
Caused by prolonged acid damage to oesophagus- can cause adenocarcinomas

Question 12

What muscles are found in the oesophagus and what is their function?

Answer 12

Circular muscle
Longitudinal muscle
These muscles cause peristalsis

Question 13

What is the gastro oesophageal junction?

Answer 13

Theres an epithelial transition
Diaphragm prevents reflux- pinches lower oesophagus
Stomach lies at an angle which also prevents acid reflex
A zigzag (Z line) is found at the junction of oesophagus and gastric mucosa
Gastric folds can be found at gastric mucosa- these increase the surface area of epithelium so more digestion and absorption occurs

Question 14

What are the stages of swallowing?

Answer 14

Stage 0: Oral phase

• chewing and saliva prepare bolus
• both oesophageal sphincters constrict

Stage 1: Pharyngeal phase

• Pharyngeal musculature guides food bolus towards oesophagus
• Both oesophageal sphincters open

Stage 2: Upper oesophageal phase

• Upper sphincter closes
• Superior circular muscle rings contract and inferior rings dilate
• Sequential contractions of longitudinal muscle

Stage 3: Oesophageal phase
- Lower sphincter closes as food passes through

Question 15

What is the role of the stomach?

Answer 15

Breaks down for into smaller particles (acid and pepsin)
Holds food, releasing it in controlled steady rate into duodenum
Kills parasites and certain bacteria

Question 16

What are the different pats of the stomach and what do they contain?

Answer 16

Cardia and pyloric region- mucus only
Body and fundus- Mucus, HCl, pepsinogen
Antrum: gastrin

Question 17

What structure invaginate into mucosa of stomach?

Answer 17

Tubular glands

Question 18

How much acid is produced by the stomach a day?

Answer 18

2L/ day
150mM H+
pH of epithelial surface = 6-7
pH of lumen= 1-2

Question 19

What coats the stomach?

Answer 19

Mucins provide gel coating

HCO3- gets trapped in mucus gel

Question 20

What contractions occur in the stomach?

Answer 20

20% peristalsis:

• propels chyme towards colon
• more powerful as you move from lower oesophageal sphincter to pyloric sphincter
• ANS essential

80% segmentation

• weaker
• moves fluid chyme towards pyloric sphincter
• solid chyme pushed back to body
• stretching activates enteric nervous system

Question 21

What 2 main cells can be found in the stomach?

Answer 21

Chief cell

Parietal cell

Question 22

What is the function of the gastric chief cell?

Answer 22

Protein secreting epithelial cell
Abundant RER
Golgi packaging and modifying for export
Masses of apical secretion granules
Secretes pepsinogen

Question 23

What is the role of the parietal cell?

Answer 23

Resting parietal cell:

• many mitochondria
• cytoplasmic tubulovesicles (contains H+/K+ ATPase )
• Internal canaliculi which extend to apical surface

Secreting parietal cell:

• Tubulovesicles fuse with membrane and secrete HCl into lumen
• Microvilli project into canaliculli

Question 24

How does the parietal cell secrete HCl into the lumen?

Answer 24

CO2 from capillaries/ interstitial fluid moves into parietal cell
CO2 combines with water to form H+ and HCO3- via carbonic anhydrase
K+ moves in from lumen and H+ moves out into lumen via H+/K+ ATPase
K+ moves in from capillaries/ interstitial fluid into parietal cell
Cl- moves into cell as HCO3- moves out of cell
K+ combines with Cl- and this is secreted into the lumen

Question 25

What triggers HCl secretion?

Answer 25

When histamine is released, it binds to histamine receptors on the surface of parietal cells causing HCl to be secreted

Question 26

How is pepsin formed?

Answer 26

HCl breaks pepsinogen down to pepsin

Question 27

What is gastrin?

Answer 27

found in the pyloric antrum
Its a local peptide hormone
It stimulates histamine release from chomaffin cells (found in lamina propria) which causes HCl secretion

Question 28

What are the phases of gastric secretion?

Answer 28

Cephalic phase: thought, sight, smell and taste stimulates vagus nerve which stimulates parietal cell via ACh which causes secretion of HCl. Histamine and gastrin also contribute to HCl secretion

Gastic phase: food enters stomach and stretch and chemoreceptors sense food in the stomach and send signal to brain. Signal returns via vagus nerve and causes acid secretion

Intestinal phase: 2 things happen- inhibition of gastric acid and stimulation of gastric acid:

• Enterogastric reflex: Food reaches duodenum and signal via vagus nerve causes inhibition of secretion of HCl and pepsin via gastrin inhibitory peptide, cholecystokinin and secretin
• In excitatory intestinal phase, protein concentration in duodenum stimulates gastrin secretion

Question 29

What drugs are used to decreases acid secretion?

Answer 29

Omeprazole- proton pump inhibitor (H+/K+ ATPase inhibitors) and prevent HCl secretion
Ranitidine- Blocks the gastrin receptor (H2 receptor) and prevents histamine release so prevents acid secretion