8.1: Upper gastrointestinal tract Flashcards
Digestion is
The process of breaking down macromolecules to allow absorption
Absorption is
The process of moving nutrients and water across a membrane
4 basic layers of gut wall
Mucosa: epithelium
Submucosa : connective tissue
Muscularis : smooth muscle
Serosa/Adventitia : connective tissue with or without epithelium
How many teeth are in the oral cavity
32
Composition of oral cavity
8 incisors
4 canines
8 premolars
12 molars
What muscle is present in the oral cavity
Massater muscle - largest jaw muscle
-responsible for biting
Function of salivary glands
First step of digestion
Food mixed with saliva
Lingual lipase - fat digestion
Salivary amylase - carb digestion
What 2 muscle types are present in the tongue
Intrinsic and extrinsic muscles
What are intrinsic muscles in the tongue responsible for
Fine motor control and moving food
What are extrinsic muscles of the tongue responsible for
Gross movement of tongue (in, out, up, down)
Assist mechanical digestion
Function of the oesophagus
Conduit for food, drink and swallowed secretions from pharynx to stomach
3 characteristics of oesophageal epithelium
Non-keritanising
Wear and tear lining - extremes of temp and texture
Lubrication - mucus secreting glands and saliva
2 characteristic of oesophageal muscle
Tonically active
Swallowing centre
2 functions of oesophageal muscle
Peristalsis
Circular muscle
4 stages of swallowing
Stage 0: oral phase
Stage 1: pharyngeal phase
Stage 2: upper oesophageal phase
Stage 3: lower oesophageal phase
What occurs In stage 0 of swallowing
Chewing and saliva prepare bolts
Both oesophageal sphincters constricted
What occurs in stage 1 of swallowing
Pharyngeal musculature guides food bonus towards oesophagus
Both oesophageal sphincters open
What occurs in stage 2 of swallowing
Upper sphincter closes
Superior circular muscle rings contract and inferior rings dilate
What occurs in stage 3 of swallowing
Lower sphincter closes as food passes through
3 functions of gastro-oesophageal junction
Reflux - prevented by diaphragm
Epithelial transition
Gastric folds - rugae
Why are gastric folds present?
To increase surface area of epithelium of the gastrointestinal tract so more digestion and more absorption can occur
3 functions of the stomach
Breaks food into smaller particles (acid and pepsin)
Holds food, releasing it in controlled steady rate into duodenum
Kills parasites and certain bacteria
What do the cardia and pyloric region of the stomach secrete
Mucus only
What do the body and fundus of the stomach secrete
Mucus, HCL, Pepsinogen
What does the antrum of the stomach secrete
Gastrin
How much of acid does the stomach produce per day
2L/day
What are mucins
Gel coating
HCO3- trapped in mucus gel
pH at epithelial surface
6-7
pH at lumen of stomach
1-2
Two types of movement in stomach
Peristalsis
Segmentation
Process of Peristalsis
Propels chyme towards colon
More powerful as moved from LOS to pyloric sphincter
ANS essential
Comparison of segmentation to peristalsis
Weaker
Fluid chyme towards pyloric sphincter
Solid chyme pushed back to body
Stretching activates enteric NS
Two types of stomach cells
Chief cell
Parietal cell
Characteristics of chief cell
Protein-secreting epithelial cell
Abundant RER
Golgi packing and modification for export
Masses of apical secretion granules
Secretes pepsinogen
Characteristics of parietal cell at rest
Many mitochondria - lots of protein pumps
Internal canaliculi (secretory surface)
Cytoplasmic tubulovesicles (cont. H+/K+ ATPase)
Characteristics of parietal cell during secretion
Microvilli project into canaliculi
Tubulovesicles fuse with membrane
What do cheif cells secrete
Pepsinogen
Needs HCL to change into pepsin
Function of gastrin in the stomach
Stimulates release of histamine from chromaffin cells (lamina propria)
3 Phases of gastric secretion
Cephalic phase
Gastric phase
Intestinal phase
In the cephalic phase of gastric secretion
Though, sight, smell and taste of food stimulates pathways transmitted by vagus nerve
Vagus nerve activates parietal cells through ACH to trigger whole cascade
In the gastric phase of gastric secretion
Food in stomach causes stretch and chemo-receptors involved
Vagus nerve sends signals to stomach to activate acid secretion
In the excitatory intestinal phase of gastric secretion
Once the chyme with pH less than 2 reaches the duodenum
Signal is transmitted by the vagus nerve and this causes secretion of hormones that inhibit the secretion of gastric HCl and pepsin too
These hormones are Gatric inhibtory peptide, Cholecystokinin and Secretin
How might you produce a useful drug to decrease acid secretion -
Omeprazole - stops K+/H+ pump
Ranitidine - stops histamine from binding to receptor
Which vertebrae is the oesophagus between?.
C5 and T10
Three subdivisions of the oesophagus
Cervical oesophagus- cricopharyngeal muscle to suprasternal notch
Thoracic oesophagus- suprasternal notch to diaphragm
Abdominal oesophagus - diaphragm to cardia of stomach
What is the Z line of the oesophagus
Line where the pink mucosa of the oesophageal sqaumous epithelium meets the red mucosa of the gastric columnar epithelium
What is the significance of this Z line in Barrett’s oesophagus
Here the epithelium of the lower oesophagus undergoes metaplasia
So gastric mucosa extends to oesophagus, meaning it would be important to determine the Z line in these cases
Is the upper or lower oesophageal sphincter a true sphincter?
Upper
Is skeletal muscle found in the upper or lower oesophagus?
Both
Is smooth muscle found in the upper or lower oesophagus
Lower
Why does this 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
Why is a hiatus hernia a risk factor for developing cancer of the oesophagus?
Because the opening of the diaphragm causes it to be larger and so there is a portion of the stomach that slips into the chest which prolongues exposure to the lower oesophagus, associating with acid reflux
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
What allows pH of epithelium surface to be between 6 and 7 when lumen is between 1-2?
Mucus coating with HCO3- trapped in mucus gel
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% contractions
Describe the nervous stimulation of peristalsis?
Activated by ANS
Describe the nervous stimulation of segmentation?
Stretching activated enteric nervous system
Explain how the parietal cells secrete HCl?
Na+/K+ pump, transports Na+ into interstitial fluid from the parietal cell
K+ transported from interstitial fluid into the parietal cell and then into the canncaliculi that have fused with the tubulovesicles
CO2 taken up by parietal cells and reacts with H20 using carbonnic anhydrase, forming H+ and HCO3-
HCO3- transported out by AE1 antiporter and Cl transported into the parietal cell and then into cannaliculi
H+/K+ ATPase transports H+ into the canaliculi and moves K+ from the canaliculi back into the parietal cell
How is this HCl secretion triggered?
H2 receptors which are found on the surface of the parietal cells
When histamine gets released from different triggers, this is detected by the H2 receptors which starts the process of HCl secretion
What is the enterogastric reflex?
Nervous reflex where stretching of the wall of the duodenum results in inhibition of gastric motility and reduced rate of emptying of the stomach
It is a feedback mechanism used to regulate the rate at which partially digested food leaves the stomach and enters the small intestine
What is the mechanism of action of Omeprazole ?
Blocks protein pumps (H+/K+ ATPase)
What can Omeprazole be used as a treatment for?
Indigestion, heartburn and acid reflux
What is the mechanism of action of Ranitidine?
Blocks the H2 receptors to prevent the triggering of the whole cascade by Histamine
Would chyme fatty acid content and protein content increase or decrease acid secretion in the stomach?
Decrease
