Oesophagus and stomach Flashcards
What are the structural layers of the gut wall?
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
How does gut wall change depending on region of the body?
type of epithelium will change
What is the role of submucosal, secretory glands and nerve plexuses in the gut?
submucosal glands secrete mucus to lubricate and propel food through the gut
secretory glands deliver enzymes to the gut
nerve plexus drives muscle contraction
Where does the oesophagus start and end?
start at C5
end at T10 where it joins stomach in the abdomen
mostly thoracic structure
What nerve is close to the oesophagus? What is its function and what is the risk?
recurrent laryngeal nerve
this controls voice projection
damage to oesophagus can damage the nerve and associated blood vessels
What is the function of the oesophagus?
conduit for food, drink and swallowed secretions from pharynx to stomach
does not facilitate absorption so must be robust
What is the structure and function of the epithelium?
stratified squamous
non keratinising
wear and tear lining (extremes of temperature and texture)
mucus/saliva secreting glands to lubricate the bolus for easy passage
What is the structure and function of the UOS and LOS?
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 §
What is the structure and function of the muscularis layer?
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
What happens if the food bolus is too large?
second peristaltic wave to ensure food reaches the stomach
this is more centrally driven by the brain
Describe the structure of the gastro-oesophageal junction
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
What structure prevents reflux?
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
Why is reflux common in pregnancy?
small part of oesophagus is in the abdomen as it is pushed into the thorax
therefore pressure increases and more acid is pushed up
What is the function of the stomach?
- 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
What is the structure of the stomach? What does each part of the stomach produce?
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
What is the cardiac and pyloric regions?
immediately entering and leaving the stomach respectively
What cells are found in the antrum?
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
What cells are found in the body and fundus?
Blue cells
acid producing cells
What cells are found in the cardia and pyloric region?
Blue cells
mucus producing cells with mucin granules
Describe blue cell function and why?
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
What is peristalsis in the stomach?
20% of stomach contractions
propel chyme to colon from LOS to pyloric sphincter
ANS coordinates motion via vagus nerve - central coordination
What is segmentation in the stomach?
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)
What are gastric chief cells?
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
How much acid does the stomach make / day?
2L
150mM of H+
