Oesophagus and stomach Flashcards

1
Q

What are the structural layers of the gut wall?

A

Mucosa:

  • epithelium
  • lamina propria (loose connective tissue)
  • muscularis mucosae

Submucosa:
- connective tissue (contains nerve plexus)

Muscularis: smooth muscle (contain nerve plexus)
circular above longitudinal layer
Serosa/adventitia: connective tissue and epithelium

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2
Q

How does gut wall change depending on region of the body?

A

type of epithelium will change

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3
Q

What is the role of submucosal, secretory glands and nerve plexuses in the gut?

A

submucosal glands secrete mucus to lubricate and propel food through the gut
secretory glands deliver enzymes to the gut
nerve plexus drives muscle contraction

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4
Q

Where does the oesophagus start and end?

A

start at C5
end at T10 where it joins stomach in the abdomen
mostly thoracic structure

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5
Q

What nerve is close to the oesophagus? What is its function and what is the risk?

A

recurrent laryngeal nerve
this controls voice projection
damage to oesophagus can damage the nerve and associated blood vessels

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6
Q

What is the function of the oesophagus?

A

conduit for food, drink and swallowed secretions from pharynx to stomach
does not facilitate absorption so must be robust

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7
Q

What is the structure and function of the epithelium?

A

stratified squamous
non keratinising
wear and tear lining (extremes of temperature and texture)
mucus/saliva secreting glands to lubricate the bolus for easy passage

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8
Q

What is the structure and function of the UOS and LOS?

A

upper oesophageal sphincter
- skeletal muscle
lower oesophageal sphincter
- skeletal and smooth muscle
At rest, both are tonically active - constricted
Swallowing centre in brain recognises swallowing/ingestion and causes relaxation of sphincters
More powerful effect on UOS as mostly skeletal muscle §

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9
Q

What is the structure and function of the muscularis layer?

A

Circular and longitudinal muscle in oesophageal wall
Local peristaltic wave in response to bolus
Nervous stimulus contracts muscle above and relaxes muscle below bolus
Independent of gravity

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10
Q

What happens if the food bolus is too large?

A

second peristaltic wave to ensure food reaches the stomach

this is more centrally driven by the brain

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11
Q

Describe the structure of the gastro-oesophageal junction

A

Epithelial transition from stratified squamous to simple columnar - more conducive to absorption
Gastric folds called rugae which can expand to accommodate food and form a smooth lining, or fold to allow stomach to decrease in size

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12
Q

What structure prevents reflux?

A

diaphragm

  • acts as LOS
  • less well defined sphincter but diaphragm and fold of stomach when empty cause a narrow opening to stomach
  • food bolus causes the diaphragm to relax and stomach to fill which increases the size of the opening
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13
Q

Why is reflux common in pregnancy?

A

small part of oesophagus is in the abdomen as it is pushed into the thorax
therefore pressure increases and more acid is pushed up

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14
Q

What is the function of the stomach?

A
  • break food down macromolecules to smaller particles by acid/pepsin
  • hold food and release at steady controlled rate into duodenum
  • kill parasites and certain bacteria a first line of defence for oral route
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15
Q

What is the structure of the stomach? What does each part of the stomach produce?

A

epithelial cells invaginate into the mucosa into tubular glands
body and fundus - mucus, HCl and pepsinogen
antrum - gastrin (facilitate stomach function)
cardia and pyloric region - mucus

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16
Q

What is the cardiac and pyloric regions?

A

immediately entering and leaving the stomach respectively

17
Q

What cells are found in the antrum?

A

Blue cells - mucus producing cells with lots of bicarbonate
Purple cells - pepsinogen producing as precursor of pepsin
Gastrin producing cells - high [] of these to stimulate acid production

18
Q

What cells are found in the body and fundus?

A

Blue cells

acid producing cells

19
Q

What cells are found in the cardia and pyloric region?

A

Blue cells

mucus producing cells with mucin granules

20
Q

Describe blue cell function and why?

A

located close to stomach contents (line stomach wall and glands)
mucus producing cells with lots of bicarbonate to neutralise stomach acid to prevent damage to stomach cells
keep pH at 6-7 despite 1-2 stomach contents

21
Q

What is peristalsis in the stomach?

A

20% of stomach contractions
propel chyme to colon from LOS to pyloric sphincter
ANS coordinates motion via vagus nerve - central coordination

22
Q

What is segmentation in the stomach?

A

80% stomach contractions
weaker, less coordinated motion
fluid chyme toward pyloric sphincter, solid chyme pushed back to body
mixing
stretching activates enteric NS (local contraction via nervous stimulation)

23
Q

What are gastric chief cells?

A

protein secreting epithelial cell
abundant rER
Golgi pack and modify for export
Lots of apical secretion granules of pepsinogen
located at tubular invaginations of epithelial surface

24
Q

How much acid does the stomach make / day?

A

2L

150mM of H+

25
Q

What is the function of mucin granules?

A

make mucus that traps HCO3-

26
Q

What are parietal cells?

What are their resting and secreting states?

A

acid secreting cell

RESTING:
lots of mitochondria (ATP)
cytoplasmic tubulovesicles (contain H/K ATPase) - long, string like
internal canaliculi (extend to apical surface) - large reservoirs close to stomach lumen

SECRETING:
tubulovesicles fuse with membrane and microvilli project into canaliculi
canaliculi combine and project outwards of stomach lumen

27
Q

How does parietal cell make acid?

A

Na/K ATPase on basal membrane pumps in lots of K to drive the movement of H+ against its concentration gradient into the stomach lumen via H/K ATPase (in TVs)
H/Cl ATPase pumps Cl- into lumen

Increased carbonic anhydrase produces H+ from CO2 and H2O delivered by blood
HCl in lumen of stomach creates acidic environment

28
Q

What is the effect of inhibition of CA?

A

decrease acid production

decrease capacity to produce H+ ions

29
Q

How do chief and parietal cells interact?

A

acid produced by parietal cells activates pepsinogen and converts it to pepsin so that it can break down protein

30
Q

Where is gastrin secreted and why?

A

pyloric antrum

gastrin is an endocrine hormone –> enters blood and return to stomach to stimulate acid production via production of histamine

it causes chromaffin cells in the lamina propia to release histamine –> histamine is a stimulus for parietal cell acid production

31
Q

What is the cephalic phase of gastric secretion?

A

STIMULATE
conditioned response to thought, sight, smell and taste of food to prepare for arrival of food
- brain responds to sensory stimuli
- stimulates parasympathetic vagus nerve to release ACh
–> acid/pepsinogen production
–> chromaffin (ECL) cells release histamine
- gastrin release

32
Q

What is the gastric phase of gastric secretion?

A

STIMULATE
food in the stomach activates stretch and chemoreceptors
- local response is more powerful: plexus in submucosal and mucosal layer directly activate muscles, glands, pepsin and acid release
- also central control as stomach distension activates vagus nerve

33
Q

What is intestinal phase of gastric secretion?

A

INHIBIT
Chyme pH and chemical components from stomach sensed by intestine (pH<2) that sends impulses via central nerve to inhibit effects on stomach and cause enterogastric reflex

STIMULATE
excitatory if high protein [] in duodenum –> stimulates gastrin secretion

34
Q

What is the enterogastric reflex?

A

cells in small intestine produce hormones to inhibit effect on stomach to switch off acid/pepsinogen production

hormones: (enterogastrones)
- secretin
- cholescystokinin
- gastric inhibitory peptide

35
Q

Target for drug to decrease acid secretion?

A

ACh
histamine
gastrin
acid producing machinery

36
Q

What drugs for acid reflux and stomach ulceration?

A

omeprazole - proton pump inhibitor

ranitidine - histamine receptor (from ECL cell) antagonist

37
Q

What would decrease stomach acid secretion?

A

chyme fatty acid content