Gastric Motility and Pancreatic Function Flashcards
Where do the peristaltic waves in the stomach occur?
From body to antrum
Describe contraction in the body of the stomach?
Weak contraction due to thin muscle - no mixing occurs
Describe contraction in the antrum of the stomach?
Powerful contraction due to thick muscle
What is the 2 main roles of the pyloric sphincter contraction in gastric motility?
Allows only small amounts of gastric content to enter duodenum
Keeps food content in stomach and forces antral contents back towards body to mix and break down
How is peristaltic rhythm generated? + length
Generated by pacemaker cells in the longitudinal muscle layer
~3/min
What are slow waves caused by?
Spontaneous depolarisation/repolarisation
What is the slow wave rhythm known as?
Basic electrical rhythm (BER)
How is slow waves conducted?
Through gap junctions along the longitudinal muscle layer
How does contraction work?
Slow wave depolarisation subthreshold which requires further depolarisation to induce APs which causes contraction
How is the strength of contraction determined?
By the number of APs/waves
How does distension of the stomach wall affect contraction?
Distension of the stomach wall causes a stretch –> detection of solid food in stomach which causes long/short reflexes –> an increased contraction
What affect does gastrin have on contraction?
Increases contraction
What affect does fat/acid/amino acid/hypertonicity in the duodenum?
Causes inhibition of motility
How is acid neutralised in the duodenum?
Bicarbonate secretion from Brunner’s Gland duct cells (submucosal glands)
What happens when acid is in the duodenum?
Triggers long (vagal) and short (ENS) reflexes = HCO3 secretion Release of secretin from S cells = HCO3 secretion from pancreas and liver
Why is acid neutralisation essential in the duodenum?
Duodenum doesn’t have the same protection as the stomach against HCl because the stomach has a thick mucus layer and the duodenum doesn’t
How is elevated pH maintained in the duodenum?
By only a small amount of food being allowed to pass into the duodenum
What affect does secretin have?
Inhibits gastrin release and inhibits acid production
Where is the head of the pancreas located?
In the curvature of the duodenum
What is the endocrine portion of the pancreas?
Pancreatic islets (islets of Langerhans) Cells produce insulin, glucagon and somatostatin
What is the exocrine portion?
Acinar cells = lobules
How are lobules connected?
By intercalated ducts –> intralobular ducts –> interlobular ducts –> main pancreatic duct –> common bile duct –> hepatopancreatic ampulla (sphincter of Oddi) –> duodenum
What is the endocrine portion responsible for?
The control of metabolism
Is exocrine inside or outside the body?
Outside but inside the lumen of the gut
What is the sphincter of Oddi responsible for?
Pancreatic juice and bile into duodenum
What shape are acinar cells?
Triangular cells which join together to form a spherical structure
What are the 2 ducts that join at the hepato-pancreatic ampulla?
Common bile duct
Pancreatic duct
What is the exocrine portion responsible for?
Digestive function of pancreas
What is the function of the exocrine pancreas?
Secretion of bicarbonate by duct cells
Secretion of digestive enzymes by acinar cells
What do acinar cells contain?
Digestive enzymes stored as inactive zymogen granules
What do zymogens do?
Prevents autodigestion of pancreas
What does enterokinase do?
Converts trypsinogen to trypsin
Where are enterokinases?
Bound to brush border of duodenal enterocytes
What does trypsin do?
Converts all other zymogens to active forms
What do proteases do?
Cleave peptide bonds
What do nucleases do?
Hydrolyse DNA/RNA
What do elastases do?
Digestion of collagen
What do phospholipases do?
Turns phospholipids into fatty acids
What do lipases do?
Turns triglycerides into fatty acids + glycerol
What does a-amylase do?
Turns starch to maltose + glucose
What is bicarbonate secretion stimulated by?
Secretin
When is secretin released?
In response to acid in duodenum
What is zymogen secretion stimulated by?
Cholecystokinin (CCK)
When is CCK released?
In response to fat/amino acids in duodenum
How is neural control triggered?
By arrival of organic nutrients in duodenum
