Upper GI Tract Flashcards
What is digestion?
process of breaking down macromolecules to allow absorption
What is absorption?
process of moving nutrients & water across a membrane
What is the route of food through the GI system?
mouth ➜ oesophagus ➜ stomach ➜ duodenum ➜ jejunum ➜ illeum ➜ caecum ➜ ascending colon ➜ transverse colon ➜ descending colon ➜ sigmoid colon ➜ rectum ➜ anus
What are the glands in the mouth?
- parotid
- sublingual
- submandibular
What is the basic structure of the gut wall?
- mucosa
- submucosa
- muscularis
- serosa/adventitia
What is the mucosa of the gut wall made up of?
- epithelium
- lamina propria (loose connective tissue)
- muscularis mucosae
What is the submucosa of the gut wall made of?
connective tissue containing nerve plexus
What is the muscularis of the gut wall made of?
smooth muscle containing nerve plexus
What is the serosa / adventitia of the gut wall made of?
connective tissue +/- epithelium
How many teeth in the oral cavity altogether?
32
How many incisors in the oral cavity altogether?
8
How many canines in the oral cavity altogether?
4
How many premolars in the oral cavity altogether?
8
How many molars in the oral cavity altogether?
12
What is the masseter muscle?
- largest jaw muscle
* responsible for biting
How many muscles control the position of the mandible?
several
What is the function of the salivary glands?
start digestion of food
How do the salivary glands digest food?
release of:
• saliva (aq secretion + digestive enzymes)
• lingual lipase (fat digestion)
• salivary amylase (carb digestion)
What is the function of the intrinsic muscles of the tongue?
- fine motor control
* moving food
What is the function of the extrinsic muscles of the tongue?
- gross movement of tongue (in out up down)
* assist mechanical digestion
What is the function of the oesophagus?
Conduit for food, drink & swallowed secretions from pharynx to stomach
What vertebrae does the oesophagus span across?
C5 to T10
What are the features of the epithelium of the oesophagus?
- Non-keratinising
- ‘Wear & Tear’ lining (extremes of temp & texture)
- Lubrication – Mucus secreting glands (& saliva)
What are the features of the muscle of the oesophagus?
- Tonically active
- Swallowing centre
- Peristalsis (circular muscle pushes, longitudinal muscle propagates)
What are the sphincters of the oesophagus?
- upper oesophageal
* lower oesophageal
What is Barret’s oesophagus?
pre-cancerous condition of the oesophagus, starts at the Z line of oesophagus
What is the Z line of the oesophagus?
the squamocolumnar junction (SCJ), the transition from the squamous oesophageal mucosa to the columnar mucosa lining the stomach
What can cause Barret’s oesophagus?
acid reflux
What is the gastro-oesophageal junction?
epithelial transition between oesophagus and stomach
What is the function of the gastro-oesophageal junction?
- prevents acid reflux by diaphragm + angle of stomach to oesophagus
- protects against stomach acids
What is the function of the gastric folds in the lining of the stomach?
gastric folds called rugae increase surface area
What are the 4 stages of swallowing?
- stage 0 : oral phase
- stage 1 : pharyngeal phase
- stage 2 : upper oesophageal phase
- stage 3 : lower oesophageal phase
What happens in Stage 0 of swallowing?
- chewing & saliva prepare bolus
* both oesophageal sphincters constricted
What happens in Stage 1 of swallowing?
- Pharyngeal musculature guides food bolus towards oesophagus
- Both oesophageal sphincters open
What happens in Stage 2 of swallowing?
• Upper sphincter closes
• Superior circular muscle rings contract & inferior rings dilate
• Sequential contractions of
longitudinal muscle
What happens in Stage 3 of swallowing?
• 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 & certain bacteria
• Invaginates into mucosa – Tubular glands
What are the major anatomic parts of the stomach?
- fundus
- body
- cardia
- pylorus: pyloric antrum, canal + sphincter
What is the epithelial lining of the stomach made up of?
simple columnar
What parts of the stomach only produce mucus?
pylorus + cardia
What parts of the stomach produce mucus, HCL + pepsinogen?
body + fundus
What parts of the stomach produce gastrin?
pyloric antrum
How much acid does the stomach produce?
- 2L/day
* 150mM H+ (3 mill x that in blood)
What are mucins in the stomach?
• HCO3- trapped in mucus gel Pepsinogen HCl
What is the pH of the stomach’s epithelial surface vs. the lumen?
- Epithelial surface = 6-7
* Lumen = 1-2
What is peristalsis?
- Series of wave-like muscle contractions that move food
- Propels chyme towards colon
- Pylorus must relax for peristaltic wave - otherwise spasm occurs + food can’t stay down
What percent of stomach contractions are peristalsis?
20%
What is segmentation?
- Weaker stomach muscle contractions
- Fluid chyme towards pyloric sphincter
- Solid chyme pushed back to body
- Stretching activates enteric nervous system
What percent of stomach contractions are segmentation?
80%
What is the importance of the mucus layer in the stomach?
protects epithelium from being damaged by acid
What muscles are responsible for segmentation?
circular muscles
What muscles are responsible for peristalsis?
longitudinal muscles
What is a gastric chief cell?
protein-secreting epithelial cell
What is the importance of acid in the stomach?
converts pepsinogen to active form pepsin
What are some features of gastric chief cells?
- abundant RER
- golgi packaging + modifying for export
- masses of apical secretion granules
What is the function of gastric chief cells?
secretes pepsinogen
What are parietal cells?
acid-secreting epithelial cells in the stomach
What are the two types?
- resting
* secreting
What are the features of a resting parietal cell?
- Many mitochondria (requires lots of ATP)
- Cytoplasmic tubulovesicles (contain H+/K+ ATPase)
- Internal canaliculi (extend to apical surface)
What are the features of a secreting parietal cell?
- Tubulovesicles fuse with membrane
* Microvilli project into canaliculi
How would inhibition of H+ carbonic anhydrase influence acid secretion in the stomach?
decrease acid secretion
What is Step 1 of HCL acid secretion in the parietal cells?
• CO2 + H2O –> H2CO3
enzyme : CARBONIC ANHYDRASE
• H2CO3 –> H+ + HCO3
== formation of H+ ions !!!
Why is carbonic acid used to form H+ ions instead of water?
carbonic acid is a better source of H+ than water
What is Step 2 of HCL acid secretion in the parietal cells?
- cell exchanges HCO3- for Cl- ion on basal side
- HCO3- diffuses into venous blood
- causes alkaline tide phenomenon
What is Step 3 of HCL acid secretion in the parietal cells?
• K+ and CL- ions diffuse into canaliculi
What is Step 4 of HCL acid secretion in the parietal cells?
• H+ ions pumped out of cell into canaliculi + exchanged for K+ ions via H+ / K+ ATPase
What is Step 5 of HCL acid secretion in the parietal cells?
- no. of receptors increase on the lumenal side by fusion of tubulovesicles during activation of parietal cells + removed during deactivation
- receptor maintains a million-fold difference in [H+]
What provides the ATP for Step 4 of HCL acid secretion in parietal cells?
numerous mitochondria
What is pepsinogen?
• powerful and abundant protein digestive enzyme
• secreted by the gastric chief cells as a proenzyme
• converted by gastric acid in the gastric lumen to
the active enzyme pepsin
What is gastrin?
- stimulates secretion of gastric acid by parietal cells
- released by G cells in the pyloric antrum of the stomach, duodenum, and the pancreas
- stimulates histamine release from chromaffin cells (lamina propia)
What can an abnormal increase in gastrin cause?
ulcers
