The oesophagus and stomach Flashcards
What are the layers of the gut wall?
Mucosa
Submucosa
Muscularis
Serosa
What does the mucosa contain?
Epithelia
Lamina propria
Muscularis mucosae
What does the submucosa contain?
Connective tissue with nerve plexi - drives movement of food bolus
What does the muscularis contain?
Smooth muscle, with nerve plexi - for movement
What does the serosa contain?
Connective tissue - holds gut to body wall
What is the function of the oesophagus?
Thoracic structure that allows food to travel from mouth (pharynx) to stomach
Where does the oesophagus originate and terminate? Which structures does it pass by? Why is this a problem?
C5, ends at T10
Passes close to the trachea, aorta and diaphragm
Any oesophageal problem can affect these structures
How are the epithelia specialised for its function?
Non-keratinising
Wear and tear lining
Lubrication - mucous secreting glands
How is oesophageal muscle specialised for its function?
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
How is oesophageal muscle specialised for food bolus movement?
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
Describe the structure of the gastro-oesophageal junction
Where oesophagus meets stomach.
Epithelial transition - oes to stom
- stratified squamous to columnar
Presence of folds
- Gastric rugae
Describe the function of the gastro-oesophageal junction, the rugae and summarise its states.
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
How is acid-reflux meant to be prevented?
Diaphragm contracts
But can fail as fetus pushes stomach upwards, leading to pressure differences and causing acid to move upwards.
What are the main functions of the stomach?
Break food into smaller particles
Hold food and release ar controlled rate
Kill parasites and certain bacteria
Describe the structure of the stomach, distinguishing between the functional regions and their functions
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
Describe the acid produced by the stomach and methods to protect against it.
2L a day,
Stomach lining has mucosal cells that release mucus with HCO3-, this protects the cells from the acid
How is food moved in the stomach?
Peristalsis
- ANS - central
- 20pc of contractions
Segmentation
- ENTERIC NS - local
- Weaker
- Allows fluid to move to pyloric sphincter
- Anything solid is pushed back up
Structure of Chief cell
- Lot of RER
- Lot of Golgi
- Lot of apical secretion granules
Function of Chief cell
Pepsinogen secreting cell
Structure of parietal cell at rest and when active
Resting
- Lot of mitochondria
- Canaliculi - large reservoirs close to surface
- Cytoplasmic tubulovesicles with H+/K+ ATPase
Active
- Tubulovesicles fuse with membrane, project into canaliculi
Function of parietal cell
Acid secreting cell
When active, tubulovesicles fuse with canaliculi and allow for a large reservoir to form which can allow acid expulsion
How is acid in the parietal cell produced?
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
What occurs following acid production?
Chief cells produce pepsinogen, which is activated to pepsin by the acid.
This can then digest proteins.
Where is gastrin made and what is it used for?
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.
What are the phases of gastric secretion? Which are stimulatory or inhibitory?
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
Drug development for acid secretion redcution
Drugs that target acid secretion
Interfere with
- ACh
- Histamine - RANITIDINE
- Gastrin
- H+/K+ exchange - OMEPRAZOLE
