upper GI Tract Flashcards
Give a brief definition of digestion
Process of breaking down macromolecules to allow absorption
Absorption
Proves of moving water and nutrients across a membrane
3 sections of GI tract
- Upper- oesophagus and foregut- stomach, pancreas, gall bladder
- Mid- midgut- small intestine and part of transverse colon large intestine
- Lower- hind gut- entire colon, rectum and anus
4 layers of gut wall
Mucosa
Submucosa
Muscularis
Serous a/adventitia
Mucosa
Made of - Epithelium
- Lamina propria (loose connective tissue)
- Muscularis mucosae
Submucosa
connective tissue containing nerve plexus
Muscularis
smooth muscle containing nerve plexus
Muscle layer is divided in 2- circular (inner layer) and longitudinal (outer layer)
Serosa/adventitia
connective tissue with or without epithelium
How many teeth do we have
32 in total
- 8 incisors
- 4 canine
- 8 premolars
- 12 molars
Largest jaw muscle that is also in charge of biting
Masseter
What muscles control chewing
- Masseter muscle- largest jaw muscle and responsible for biting
- Temporalis muscle
- Others control position of mandible
What 3 salivary glands do we have and what 2 enzymes are in saliva?
- Parotid gland
- Sublingual
- Submandibular gland
- Enzymes are lingual lipase (fat digestion) and salivary amylase (carb digestion)
What 2 groups of muscles are involved with tongue and what are their functions?
- Intrinsic muscles- fine motor control and moving food
- Extrinsic- gross movement of tongue (in, out, up, down) and assist mechanical digestion
Oesophagus
Conduit for food, drink & swallowed secretions from pharynx to stomach
Describe the structure of the oesophageal epithelium and how it relates to its function?
- Non-keratinising (stratified) squamous epithelium
- Wear and tear lining to protect from acid reflux
- Lubrication of food bolus- mucus secreting glands and saliva
Describe the 2 oesophagus sphincters and describe what the Z line is?
- Tonically active
- Swallowing centre
- 2 sphincters- upper and lower
Is the upper or lower oesophageal sphincter a true sphincter?
Upper
Lower has Z line where pale pink mucosa of squamous epithelium meets red mucosa of gastric epithelium
What is the significance of this Z line in Barrett’s oesophagus?
Barrett’s oesophagus extends Z line upwards as loads of pink squamous epithelium (of the lower oesophagus) undergo metaplasia to become gastric columnar epithelium
Describe the 2 muscle types and function of oesophagus
- Peristalsis
- Circular muscle- has segmental role- allows food to remain in certain parts of oesophagus for some time
- Longitudinal muscle- propagates food movement down oesophagus
Is skeletal muscle found in the upper or lower oesophagus?
Both
smooth muscle found in the upper or lower oesophagus?
Lower
How does epithelial transition at the gastro-oesophageal junction occur and how does this develop to cancers?
Acid reflux means that the upper oesophagus is more acidic than normal
To cope with this, the squamous cells above the gastro-oesophageal junction become columnar epithelium
This change to columnar epithelium makes the cells unstable, leading to dysplasia and then becomes cancers
How is acid reflux prevented by the diaphragm?
prevented by diaphragm by pinching lower oesophagus
How does the anatomical orientation of the stomach to the oesophagus reduce the risk of acid reflux?
Stomach lies at an angle to the oesophagus
Other ligaments also suspend the gastro-oesophageal junction at an acute angle on the fringe oesophageal ligaments to prevent acid reflux
There are gastric folds called rugae- what is their purpose?
So more digestion and absorption can occur
To increase the surface area of the epithelium of the gastro intestinal tract so that more amount of digestion and more absorption can occur
Describe the 4 stages of swallowing OPUL
- Stage 0- oral phase
- Chewing and saliva prepare bolus
- Both oesophageal sphincters constricted
- Stage 1- pharyngeal phase
- Pharyngeal muscles guide food bolus towards oesophagus
- Both 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- lower oesophageal phaseLower sphincter closes as food passes through
What are the stomach’s 3 functions?
- Breaks food into smaller particles through acid and pepsin
- Holds food and releases it in controlled steady rate into duodenum
- Kills parasites and some bacteria
What are the sections of the stomach?
- Cardia and pyloric region- secretes?secretes mucus only
- Body and fundus- secretes?secrete mucus, HCl and pepsinogen
- Antrum- what does it secrete?secretes gastrin
What is the pH level of the stomach and how is the epithelium protected
pH of 1-2 in lumen- stomach produces 2L of acid a day with 150mM H+
Epithelial surface is protected by mucus layer with HCO3- trapped in the mucus gel
Peristalsis
- 20% of stomach contractions
- Propels chyme towards colon
- More powerful as it moves from LOS to pyloric sphincter
- ANS is essential
Segmentation
- 80% of stomach contractions
- Weaker
- Fluid chyme towards pyloric sphincter
- Solid chyme pushed back to body
- Stretching activates enteric NS
Which layer of muscle carries out segmentational contraction
Circular
Which layer of muscle carries out peristalsis contraction
Longitudinal
Is segmentation or peristalsis the stronger contraction
Peristalsis
Which method of contraction occurs most often
Segmentation 80%
- Where does peristalsis propel chyme to?t
Towards colon
Where does segmentation move chyme to (2)?
Fluid chyme towards pyloric sphincter
Solid chyme pushed back to the body
Describe the nervous stimulation of peristalsis?
Activated by ans
Describe the nervous stimulation of segmentation?
Stretching activated enteric nervous system
What do gastric chief cells do secrete + how are they adapted (3)?
- Secretes pepsinogen
- Protein secreting epithelial cell rich in RER
- Golgi packaging and modifying for export
- Masses of apical secretion granules
What do parietal cells secrete and how are they adapted (3)?
- Secretes HCl
- Many mitochondria (requires lots of ATP)
- Has cytoplasmic tubulovesicles which contain HCl → the vesicles contain H+/K+ ATPase pump which pumps HCl into stomach lumen
- ## Has internal canaliculi which extend to apical surface
Describe the process of HCl formation and secretion by parietal cells
1) Sodium-potassium pump brings K+ into parietal cell and Na+ out, then K+ moves into canaliculi (that have fused with the tubulovesicles)
2) CO2 taken up by parietal cells and reacts with H2O using carbonic anhydrase, forming carbonic acid which dissociates into H+ and HCO3-.
3) HCO3- transported out by AE1 antiporter and Cl transported into the parietal cell and then into cannaliculi
4) H+/K+ ATPase transports H+ into the canaliculi and moves K+ from the canaliculi back into the parietal cell
5) You get left with H+ and Cl- in canaliculi which combine to make HCl
What triggers the production and secretion of HCl? (3 things, but one of the 3 is the main one)
Histamine acting on (H2) histamine receptors on parietal cells
ACh
Gastrin
- What cells is gastrin produced by and what is the direct function of gastrin?
-
- Made by pyloric antrum by G cells
- Gastrin is a local peptide hormone
-
Stimulates histamine release from chromaffin cells (lamina propia), which triggers HCL secretion
-stimulated by distention,small peptides and amino acids via vagus nerve
What are the 3 phases of gastric secretion? CGI
- Cephalic phase, describe itThe thought, sight, smell and taste of food stimulates vagus nerve which stimulates parietal cell through ACh which starts formation of HCl (ACh can also stimulate HCl secretion along with gastrin and histamine)
- Gastric phaseFood reaches stomach, activation of stretch and chemoreceptorsThis sends signals via vagus nerve to brain which sends signals back through vagus nerve to activate HCl secretion
- Intestinal phase
Chyme reaches duodenum. Signal comes via vagus nerve which inhibits gastric HCL and pepsin through inhibitory hormones
How might you produce a useful drug to decrease acid secretion?
- Receptor blockers which block histamine receptor- cimetidine and ranitidine- block acid secretion
- K+/H+ ATPase pump inhibitors prevent HCl formation (omeprazole)
- a selective antimuscarinic, which blocks mAch receptor
Which of the following stimuli would most likely decrease acid secretion in stomach?
Protein content in meal
Chyme fatty acid content
