Upper GI tract Flashcards
What is digestion?
Process of breaking down macromolecules to allow absorption
What is absorption?
Process of moving nutrients and water across a membrane
What makes up the upper GI tract?
Oesophagus, stomach, foregut (liver, pancreas, gall bladder and part of duodenum)
What are the different layers of the gut wall?
Mucosa:
- epithelium
- lamina propria
- muscular mucosae
Submucosa:
- connective tissue (containing nerve plexus)
Muscularis:
- smooth muscle (containing nerve plexus)
Serosa/ adventitia:
- connective tissue +/- epithelium
How many teeth are in the oral cavity?
8 incisors
4 canines
8 premolars
12 molars
32 teeth in total
What is the role of salivary glands in the oral cavity?
Food mixes with saliva (aqueous secretion and digestive enzymes)
Lingual lipase secreted for fat digestion
Salivary amylase secreted for carbohydrate digestion
How is the tongue moved?
Intrinsic muscles: fine motor control and moving food
Extrinsic muscles: gross movement of tongue (in, out, up and down). Assists mechanical digestion
What is the function of the oesophagus?
Conduit for food, drink and swallowed secretions from pharynx to stomach
How is the oesophagus epithelium structured?
Has a non-keretanising squamous epithelium
Has wear and tear lining which protects from extreme temps, texture and acid reflux
Has lubrication- mucus secreting glands and saliva
What structure can be found at the top and bottom of the oesophagus?
Upper oesophageal sphincter: a true sphincter
Lower oesophageal sphincter: not sure if true or not
What is Barretts oesophagus?
Epithelium of lower oesophagus undergoes metaplasia to go from squamous to columnar
Gastric mucosa extends into oesophagus (red in colour)
Caused by prolonged acid damage to oesophagus- can cause adenocarcinomas
What muscles are found in the oesophagus and what is their function?
Circular muscle
Longitudinal muscle
These muscles cause peristalsis
What is the gastro oesophageal junction?
Theres an epithelial transition
Diaphragm prevents reflux- pinches lower oesophagus
Stomach lies at an angle which also prevents acid reflex
A zigzag (Z line) is found at the junction of oesophagus and gastric mucosa
Gastric folds can be found at gastric mucosa- these increase the surface area of epithelium so more digestion and absorption occurs
What are the stages of swallowing?
Stage 0: Oral phase
- chewing and saliva prepare bolus
- both oesophageal sphincters constrict
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 and inferior rings dilate
- Sequential contractions of longitudinal muscle
Stage 3: Oesophageal phase
- Lower sphincter closes as food passes through
What is the role of the stomach?
Breaks down for into smaller particles (acid and pepsin)
Holds food, releasing it in controlled steady rate into duodenum
Kills parasites and certain bacteria
What are the different pats of the stomach and what do they contain?
Cardia and pyloric region- mucus only
Body and fundus- Mucus, HCl, pepsinogen
Antrum: gastrin
What structure invaginate into mucosa of stomach?
Tubular glands
How much acid is produced by the stomach a day?
2L/ day
150mM H+
pH of epithelial surface = 6-7
pH of lumen= 1-2
What coats the stomach?
Mucins provide gel coating
HCO3- gets trapped in mucus gel
What contractions occur in the stomach?
20% peristalsis:
- propels chyme towards colon
- more powerful as you move from lower oesophageal sphincter to pyloric sphincter
- ANS essential
80% segmentation
- weaker
- moves fluid chyme towards pyloric sphincter
- solid chyme pushed back to body
- stretching activates enteric nervous system
What 2 main cells can be found in the stomach?
Chief cell
Parietal cell
What is the function of the gastric chief cell?
Protein secreting epithelial cell Abundant RER Golgi packaging and modifying for export Masses of apical secretion granules Secretes pepsinogen
What is the role of the parietal cell?
Resting parietal cell:
- many mitochondria
- cytoplasmic tubulovesicles (contains H+/K+ ATPase )
- Internal canaliculi which extend to apical surface
Secreting parietal cell:
- Tubulovesicles fuse with membrane and secrete HCl into lumen
- Microvilli project into canaliculli
How does the parietal cell secrete HCl into the lumen?
CO2 from capillaries/ interstitial fluid moves into parietal cell
CO2 combines with water to form H+ and HCO3- via carbonic anhydrase
K+ moves in from lumen and H+ moves out into lumen via H+/K+ ATPase
K+ moves in from capillaries/ interstitial fluid into parietal cell
Cl- moves into cell as HCO3- moves out of cell
K+ combines with Cl- and this is secreted into the lumen
