Upper GI Tract Flashcards
What is digestion?
-the process of breaking down macromolecules to allow absorption
What is absorption?
-the process of moving nutrients and water across a membrane
What are the layers of the gut wall?
(Oesophagus side)
Mucosa:
- epithelium
- lamina propria (loose connective tissue)
- muscularis mucosae
Submucosa:
-connective tissue (contains nerve plexus)
Muscularis:
-smooth muscle (contain nerve plexus)
Serosa/Adventitia:
-connective tissue +/- epithelium
How many teeth do adults have and what are they?
32 in total
- 8 incisors
- 4 canines
- 8 premolars
- 12 molars
What muscles are involved in the oral cavity chewing?
- masseter muscle- largest jaw muscle, responsible for biting
- several other muscles control the position of the mandible
What does saliva contain?
-digestive enzymes and aqueous secretion
What are the 3 salivary glands?
- parotid glands
- sublingual glands
- submaxillary gland
What are the muscles in the tongue and their function?
Intrinsic muscles:
-fine motor control & moving food
Extrinsic muscles:
- gross movement of tongue (in, out, up, down)
- assists mechanical digestion
At which C & T points does the oesophagus start and end?
-C5 and T10
What is the function of the oesophagus?
-conduit for food, drink and swallowed secretions from pharynx to stomach
What is the structure and function of the epithelium of the oesophagus?
- non-keratinising
- ‘wear & tear’ lining (extreme temp & texture)
- lubrication- mucus secreting glands (&saliva)
- nucleated superficial squamous cells
- basal cell
- basal lamina
What is the structure and function of the muscles in the oesophagus?
- tonically active
- swallowing centre
- upper oesophageal sphincter- skeletal muscle
- lower oesophageal sphincter- skeletal & smooth muscle
- peristalsis
- inner circular muscle
- longitudinal muscle
What happens at the gastro-oesophageal junction?
- reflux- prevented by diaphragm hiatus
- epithelial transition
- gastric folds- rugae
GORD
-gastro-oesophageal reflux disease
-lining changes from stratified squamous epithelium to simple columnae epithelium which secretes the mucus
What is hiatus hernia?
- when the hiatus of diaphragm large and so can’t constrict the oesophagus anymore
- part of the stomach starts migrating into the chest
- keep the gastro-oesophageal junction open, acid goes up and acid reflux
What is the purpose of the epithelial transition?
- secretion in stomach by simple columnar
- protective function of stratified squamous
Why are gastric folds present?
- absorbative and secretory function
- increased SA
What are the 4 stages of swallowing?
Stage 0- oral phase:
- chewing and alive prepare bolus
- both oesophageal sphincters constricted
Stage 1- Pharyngeal phase:
- pharyngeal musculature guides food bolus towards oesophagus
- both oesophageal sphincter open
Stage 2- upper oesophageal phase:
- upper sphincter closes
- superior circular muscle rings contract & inferior rings dilate
- sequential contractions of longitudinal muscle
Stage 3- lower oesophageal phase:
-lower sphincter closes as food passes through
What are the functions of the stomach?
- breaks food into smaller particles (acid & pepsin)
- holds food, releasing it in controlled steady rate into duodenum
- kills parasites and bacteria
What is the function of the cardia and pyloric region of the stomach?
-mucus only
What is the function of the body and fundus of the stomach?
-mucus, HCL, pepsinogen
What is the function of the antrum?
-gastrin
How much acid does the stomach produce in a day?
-2L
What are mucins?
- gel coating
- HCO3- trapped in mucus gel
What is the optimal pH at the epithelial surface and lumen of the stomach?
Epithelial surface = 6-7
Lumen = 1-2
Contrast peristalsis and segmentation in the stomach.
Peristalsis (longitudinal muscle):
- 20% of stomach contractions
- propels chyme towards colon
- more powerful as moves from LOD to pyloric sphincter
- ANS essential
Segmentation (circular muscle):
- 80% of stomach contractions
- weaker
- fluid chyme towards pyloric sphincter
- solid chyme pushed back to body
- stretches activate enteric NS
What do the chief cells of the stomach do?
Gastric chief cell:
- protein-secreting epithelial cell
- secretes pepsinogen
- pepsinogen converted to pepsin to break down proteins
- abundant RER
- golgi packaging and modifying for export
- masses of apical secretion granules
What are parietal cells?
- important in creating HCL
- many mitochondria
- cytoplasmic tubulovesicles (contain H+/K+ ATPase pump)
- internal canaliculi (extend to apical surface)
- tubulovesicles fuse with membrane
- microvili project into canaliculi
How parietal cells work?
- CO2 comes into parietal cells and mixes with water via carbonic anhydrase, broken down into H+ and HCO3-
- K+ enters cell via Na/K pump from capillaries
- K+ secreted into gastric lumen
- HCO3- enters capillaries and Cl- enters cell
- H+ into gastric lumen via H/K+ ATPase pump
- H+ combines with Cl- to make HCL
How would inhibition of carbonic anhydrase influence acid secretion in the stomach?
-decreased HCL
What role does HCL play?
-converts pepsinogen to pepsin
What is gastrin in the stomach?
- local peptide hormone secreted by the G-cells
- pyloric antrum
- stimulates histamine release from chromatin cells (lamina propia)
What are the phases of gastric secretion?
Cephalic Phase:
- stomach stimulated via vagus nerve (thought, sight, smell, taste of food)
- controls pyloric and cardiac sphincter contraction
- local stimulus via gastrin, going via bloodstream to stimulate the parietal cells
Gastric Phase:
- food in stomach- stretch & chemo-receptors
- gastric distension stimulates local reflexes
- control local reflexes
- HCL & pepsin also self-stimulate the stomach
- excess acidity (pH<2) causes less gastrin release, so inhibits stomach secretory activity
Intestinal Phase:
- sends signals to the stomach via enterohormones
- Gastric inhibitory peptides, cholecystokinin, secretin produced which are enterogastrones, play a role in entergogastric reflex and inhibit/promote HCL & pepsin
REMEMBER- nervous stimulus hormonal stimulus local stimulus -all together control stomach function
What is the excitatory intestinal phase?
-protein concentration in duodenum stimulates gastrin secretion
What affect does distension of the duodenum have?
-inhibits stomach secretory activity
How might you produce a useful drug to decrease acid secretion?
- suppress H/K+ ATPase
- Omeprazole
- Ranitidine
-somatostatin suppresses G-cell receptors
What effect will chyme fatty acid content have on acid secretion in the stomach?
- M2 receptor for ACh for parasympathetic stimulation via the vagus nerve
- histamine secreted by cells in stomach wall acts on H2 receptor, causes HCL secretion
- Gastrin stimulates G-cells
