4. The Stomach Flashcards
What are the roles of the stomach?
Storage facility
Start digestion f protein
A little bit of carb and fat digestion
Disinfect
What is the cardia of the stomach?
Opening of stomach from oesophagus
What is the antrum of the stomach?
Bottom, narrower section of stomach
What is the sphincter at the junction of stomach and duodenum?
Pyloric sphincter
What sphincter is at the junction of the oesophagus and stomach?
Lower oesophageal sphincter
What is the purpose of the right crus of diaphragm?
Close junction between oesophagus and stomach when intra abdominal pressure rises
What helps to prevent reflux of stomach contents into the oesophagus?
Receptive relaxation
LOS
Right crus of diaphragm
What is receptive relaxation?
Relaxation of proximal stomach muscles so that fundus distends, happens due to peristalsis of oesophagus
What are the layers of muscles of the stomach?
Oblique
Circular
Longitudinal
What is the epithelial surface of the stomach lined with?
- Surface mucous cells which secrete mucus, forms a layer between lumen of stomach and epithelial layer of stomach
- Gastric pits lead to gastric glands
What is the purpose of gastric glands?
Contain parietal cells (produce acid), chief cells (secrete pepsinogen), enteroendocrine cells (G cells)
What is pepsinogen?
Precursor to pepsin, activated by acid in stomach
What do G cells secrete?
HCO3 (protective against acid to stomach wall)
Gastrin
What protects the stomach wall form its acidic contents?
HCO3 - pH neutral layer
Prostaglandins - increase mucosal blood flow, support mucus layer, generally protective
Cells replaced regularly
How does the parietal cell produce acid?
Exchanges intraluminal K+ for H+, using H+K+ ATPase/proton pump
Where are the proton pumps in parietal cells located?
Within tubulovesicles
What happens during the resting phase of the parietal cells?
No acid is secreted
Tubulovesicles are not in contact with the apical membrane
How do the parietal cells move from the resting phase to the stimulated phase?
Apical membrane forms canaliculi with microvilli which then fuse with the tubulovesicles to allow secretions
What stimulates acid production in the stomach?
Sensory triggers (30%)- smell, sight, taste Gastric triggers (60%)- stretching of stomach, presence of amino acids and small peptides Intestinal triggers (10%)- chyme in duodenum, presence of partially digested proteins
How can parietal cells be ‘turned on’?
Gastrin receptors - cholecystokinin
Histamine receptors - histamine onto H2 receptor
Muscarinic receptors - vagal stimulation
How are G cells stimulates to produce gastrin?
Peptides in stomach lumen
Acetyl choline (vagal stimulation)
Gastrin releasing peptide (vagal stimulation)
What produces histamine?
Entero-chromaffin like cell
How is the entero-chromatin like cell stimulated?
Vagal stimulation
Gastrin on gastrin receptors
What is the role of D cells?
‘Turn off’ parietal cells
