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 4 main layers of the gut wall?
Mucosa
Submucosa
Muscularis
Serosa/ Adventitia
What are the three layers of the mucosa?
- epithelium
- lamina propria (loose connective tissue)
- muscularis mucosae
Which layers of the gut wall contain nerve plexuses?
Submucosa and muscularis
What are the two types of muscles found in the muscularis?
Circular and longitudinal
What is found in the submucosa?
Nerve plexuses and submucosal glands
What is found in the muscularis layer?
Longitudinal muscle
Circular muscle
Nerve plexuses
How many teeth are present in adults in total?
32
How many of each type of teeth are present in the oral cavity?
8 incisors
4 canines
8 premolars
12 molars
Which muscle is the largest jaw muscle and responsible for biting?
Masseter
What does saliva contain?
Aqueous secretion and digestive enzymes
Which digestive enzymes does saliva contain?
Lingual lipase - fat digestion and salivary amylase - carbohydrate digestion
What are the main salivary glands?
Parotid gland
Sublingual gland
Submaxillary gland
What are the intrinsic muscles of the tongue responsible for?
fine motor control & moving food
What are the extrinsic muscles of the tongue responsible for?
gross movement of tongue (in, out, up & down)
Assists mechanical digestion
What are the subdivisions of the oesophagus?
Cervical
Thoracic
Abdominal
Which vertabrae does the oesophagus lie between?
C5 to T10
What is the function of the oesophagus?
Conduit for food, drink & swallowed secretions from pharynx to stomach
Describe the epithelium of the oesophagus?
- Non-keratinising
‘- Wear & Tear’ lining (extremes of temp. & texture) - Contains mucus secreting glands
What are the muscles found at the top and bottom of the oesophagus?
Upper oesophageal sphincter and lower oesophageal sphincter
what is the role of mucus in the oesophagus?
Aids the passage of food and drink
What is the Z line in 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 the gastric mucosa extends into the oesophagus, meaning it would be important to determine the Z line in these cases
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
Is skeletal muscle found in the upper or lower oesophagus?
Both
Is smooth muscle found in the upper or lower oesophagus?
Lower
How does the anatomical orientation of the stomach to the oesophagus reduce the risk of acid reflux?
reflux is prevented by the diaphragm and the angle of the stomach to the oesophagus
What are gastric folds called and what is their purpose?
Rugae - they increase surface area so more digestion and absorption can occur
What is the role of circular and longitudinal muscle in peristalsis?
Circular muscle pushes, longitudinal muscle propagates
Which type of epithelium can tolerate acidic conditions?
Simple columnar epithelium
What happens to the level of the Z line in Barrets oesophagus?
Z line is raised due to acid reflux from the stomach
Describe the swallowing process.
Stage 0: Oral phase
- Chewing & saliva prepare bolus
- Both oesophageal sphincters constricted
Stage 1: Pharyngeal phase
- Pharyngeal musculature guides food bolus towards oesophagus
- Both oesophageal sphincters 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
Describe what happens to the upper oesophageal sphincter during each stage of swallowing?
1: Oral = Closed
2: Pharyngeal = open
3: Upper oesophageal = closed
4: Lower oesophageal = Closed
Describe what happens to the lower oesophageal sphincter during the swallowing process
1: Oral = Closed
2: Pharyngeal = open
3: Upper oesophageal = open
4: Lower oesophageal = Closed
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 & certain bacteria
What are the secretions of the cardia and pyloric regions of the stomach?
Mucus only
What are the secretions of the body and fundus regions of the stomach?
Mucus, HCl, and pepsinogen
What does the antrum of the stomach secrete?
Gastrin
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 much acid is produced per day by the stomach and what is the H+ concn. of this acid?
2L/day
150mM H+ (3 mill x that in blood)
What allows the pH of the epithelial surface to be between 6 and 7 when the lumen is between 1 and 2?
Mucus coating with HCO3- trapped in the mucus gel
Which layer of muscle carries out segmentational contraction?
circular
Which layer of muscle carries out peristalsis contraction?
longitudinal
What are the proportions of stomach contractions which are peristatic and segmental?
Peristaltic - 20%
Segmental - 80%
Which type of stomach contraction is stronger?
Peristaltic - Propels chyme towards colon
Which stomach contraction is dependant on the autonomic nervous system?
Peristalsis
What does segmentation do?
- Pushes fluid chyme towards Pyloric sphincter
- Solid chyme pushed back to body
What does the stretching due to segmentation activate?
Enteric nervous system
What does the gastric chief cell secrete?
Pepsinogen
Which cellular component is abundant in chief cells?
Rough endoplasmic reticulum and Golgi - due to protein secretion = needed for packaging, modifying and exportation
What are the parietal cells responsible for producing and secreting?
HCl and intrinsic factor
What are three structures found in parietal cells in the resting state?
Mitochondria
Internal Canaliculi
Cytoplasmic tubulovesicles
What do cytoplasmic tubulovesicles contain?
contains H+/K+ ATPase
How does the appearance of the parietal cell change in the secreting stage?
Microvilli project into canaliculi
Tubulovesicles fuse with membrane
How would the inhibition of H+ carbonic anhydrase influence stomach acid secretion?
Decrease acid secretion
What three drug types could be used to decrease stomach acid secretion?
- Carbonic anhydrase inhibitor
- Histamine receptor antagonist
- K+/H+ ATPase inhibitor
What is the name of the histamine receptor antagonist used to decrease stomach acid?
Ranitidine
What is the name of the H+/K+ ATPase inhibitor antagonist used to decrease stomach acid, heart burn and indigestion?
Omeprazole
What stimuli is most likely to decrease acid secretion in the stomach?
Chyme fatty acid content - due to the enterogastric fatty acid content
What triggers the process of HCl secretion?
The binding of histamine to histamine receptors on the parietal cells
Describe the process of HCl secretion
- Carbonic anhydrase catalyses the conversion of Water and Carbon Dioxide into H+ and HCO3-
- The Bicarbonate ion is exchanged for a Cl- ion which enters into the parietal cell, and bicarbonate into the blood
- Na+/K+ ATPase pumps sodium out the parietal cell and K+ into the cell and therefore canaliculi
- Then, the H+ ions are pumped out the Parietal cell into the canaliculi through the H+/K+ ATPase pump, as K+ ions are pumped from the canaliculi into the parietal cell
- The Cl- ions then enter the canaliculi as well through Cl- ion channels
- Combine to make HCl
What is pepsinogen?
A powerful and abundant protein digestive enzyme which is secreted by the chief cells as a proenzyme
What effect does HCl have on pepsinogen?
Converts pepsinogen into pepsin
What can an abnormal increase in gastrin cause?
Stomach ulcers
what does pepsin do?
Breaks down dietary proteins into partially digested proteins
Which part of the stomach secretes gastrin?
Pyloric antrum
What is gastrin secretion stimulated by?
Stimulated by distention, small peptides & amino acids, stimulation of vagus nerves
What does gastrin stimulate the release of?
Stimulate histamine release from chromaffin cells (lamina propia)
What is the pH of gastric venous blood?
Alkaline
What are the three phases of gastric secretion?
Cephalic
Gastric
Intestinal
How is the parietal cell adapted for this function?
It has many mitochondria
It has H+/K+ ATPase which is largely responsible for the secretion of HCl into the lumen of the stomach
HCl secreted into tubulovesicles which then fuse with the membrane of the cell and secrete HCl into lumen of stomach
Describe the cephalic phase of gastric secretion
Thought, sight, smell and taste of food stimulates gastric secretion
Vagus nerve activates parietal cells through ACh to trigger the whole cascade
Describe the gastric phase of gastric secretion
Food in stomach activates the stretch- (distension) and chemo-receptors (pH of food chemicals) - G cells secrete gastrin which stimulates HCl secretion
Signals sent to and from the brain via vagus nerve to activate the secretion of acid
Describe the 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
What are the three enterogastrones?
GIP = Gastric inhibitory Peptide
Cholecystokinin
Secretin
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 action of circular muscles in the upper oesophageal phase?
Superior circular muscle rings contract and inferior rings dilate
What is the action of longitudinal muscles in the upper esophageal phase
Sequential contractions of longitudinal muscle
